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61769477 welding-inspection-cswip-gud

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Jithu John
Jithu John

CSWIP PPT FOR EASY STUDIES

Engineering
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Welding Inspector 4/23/2007 1 of 691 Duties and Responsibilities Section 1
Main Responsibilities 1.1 4/23/2007 2 of 691 • Code compliance • Workmanship control • Documentation control
Personal Attributes 1.1 Important qualities that good Inspectors are expected to have are: •Honesty •Integrity •Knowledge •Good communicator •Physical fitness •Good eyesight 4/23/2007 3 of 691
Standard for Visual Inspection 1.1 Basic Requirements 4/23/2007 4 of 691 BS EN 970 - Non-destructive examination of fusion welds - Visual examination Welding Inspection Personnel should: • be familiar with relevant standards, rules and specifications applicable to the fabrication work to be undertaken • be informed about the welding procedures to be used • have good vision (which should be checked every 12 months)
Welding Inspection 1.2 4/23/2007 5 of 691 Conditions for Visual Inspection (to BS EN 970) Illumination: • 350 lux minimum required • (recommends 500 lux - normal shop or office lighting) Vision Access: • eye should be within 600mm of the surface • viewing angle (line from eye to surface) to be not less than 30° 30° 600mm
Welding Inspection 1.3 Aids to Visual Inspection (to BS EN 970) When access is restricted may use: • a mirrored boroscope • a fibre optic viewing system Other aids: • welding gauges (for checking bevel angles, weld profile, fillet sizing, undercut depth) • dedicated weld-gap gauges and linear misalignment (high-low) gauges • straight edges and measuring tapes • magnifying lens (if magnification lens used it should have magnification between X2 to X5) 4/23/2007 6 of 691 usually by agreement }
Welding Inspectors Equipment 1.3 Measuring devices: • flexible tape, steel rule • Temperature indicating crayons • Welding gauges • Voltmeter • Ammeter • Magnifying glass • Torch / flash light • Gas flow-meter 4/23/2007 7 of 691
Welding Inspectors Gauges 1.3 4/23/2007 8 of 691 TWI Multi-purpose Welding Gauge Misalignment Gauges Hi-Lo Gauge Fillet Weld Gauges G.A.L. S.T.D. 10mm 16mm L G.A.L. S.T.D. 10mm 16mm 0 1/4 1/2 3/4 IN HI-LOSinglePurposeWeldingGauge 1 2 3 4 5 6
Welding Inspectors Equipment 1.3 4/23/2007 9 of 691 Tong Tester AmmeterVoltmeter
Welding Inspection 1.3 4/23/2007 10 of 691 Stages of Visual Inspection (to BS EN 970) Extent of examination and when required should be defined in the application standard or by agreement between the contracting parties For high integrity fabrications inspection required throughout the fabrication process: Before welding (Before assemble & After assembly) During welding After welding
Typical Duties of a Welding Inspector 1.5 4/23/2007 11 of 691 Before Welding Preparation: Familiarisation with relevant „documents‟… • Application Standard/Code - for visual acceptance requirements • Drawings - item details and positions/tolerances etc • Quality Control Procedures - for activities such as material handling, documentation control, storage & issue of welding consumables • Quality Plan/Inspection & Test Plan/Inspection Checklist - details of inspection requirements, inspection procedures & records required
Typical Duties of a Welding Inspector 1.5 4/23/2007 12 of 691 Before Welding Welding Procedures: • are applicable to joints to be welded & approved • are available to welders & inspectors Welder Qualifications: • list of available qualified welders related to WPS‟s • certificates are valid and ‘in-date’
Typical Duties of a Welding Inspector 1.5 Before Welding Equipment: • all inspection equipment is in good condition & calibrated as necessary • all safety requirements are understood & necessary equipment available Materials: • can be identified & related to test certificates, traceability ! • are of correct dimensions • are in suitable condition (no damage/contamination) 4/23/2007 13 of 691
Typical Duties of a Welding Inspector 1.5 Before Welding Consumables: • in accordance with WPS’s • are being controlled in accordance with Procedure Weld Preparations: • comply with WPS/drawing • free from defects & contamination Welding Equipment: • in good order & calibrated as required by Procedure 4/23/2007 14 of 691
Typical Duties of a Welding Inspector 1.5 Before Welding Fit-up • complies with WPS • Number / size of tack welds to Code / good workmanship Pre-heat • if specified • minimum temperature complies with WPS 4/23/2007 15 of 691
Typical Duties of a Welding Inspector 1.5 4/23/2007 16 of 691 During Welding Weather conditions • suitable if site / field welding Welding Process(es) • in accordance with WPS Welder • is approved to weld the joint Pre-heat (if required) • minimum temperature as specified by WPS • maximum interpass temperature as WPS
Typical Duties of a Welding Inspector 1.6 During Welding Welding consumables • in accordance with WPS • in suitable condition • controlled issue and handling Welding Parameters • current, voltage & travel speed – as WPS Root runs • if possible, visually inspect root before single-sided welds are filled up 4/23/2007 17 of 691
Typical Duties of a Welding Inspector 1.6 During Welding Inter-run cleaning in accordance with an approved method (& back gouging) to good workmanship standard Distortion control • welding is balanced & over-welding is avoided 4/23/2007 18 of 691
Typical Duties of a Welding Inspector 1.6 4/23/2007 19 of 691 After Welding Weld Identification • identified/numbered as required • is marked with welder‟s identity Visual Inspection • ensure weld is suitable for all NDT • visually inspect & „sentence‟ to Code requirements Dimensional Survey • ensure dimensions comply with Code/drawing Other NDT • ensure all NDT is completed & reports available
Typical Duties of a Welding Inspector 1.6 After Welding Repairs • monitor repairs to ensure compliance with Procedure, ensure NDT after repairs is completed • PWHT • monitor for compliance with Procedure • check chart records confirm Procedure compliance Pressure / Load Test • ensure test equipment is suitably calibrated • monitor to ensure compliance with Procedure • ensure all records are available 4/23/2007 20 of 691
Typical Duties of a Welding Inspector 1.6 After Welding Documentation • ensure any modifications are on ‘as-built’ drawings • ensure all required documents are available • Collate / file documents for manufacturing records • Sign all documentation and forward it to QC department. 4/23/2007 21 of 691
Summary of Duties A Welding Inspector must: • Observe To observe all relevant actions related to weld quality throughout production. • Record To record, or log all production inspection points relevant to quality, including a final report showing all identified imperfections • Compare To compare all recorded information with the acceptance criteria and any other relevant clauses in the applied application standard 4/23/2007 22 of 691 It is the duty of a Welding Inspector to ensure all the welding and associated actions are carried out in accordance with the specification and any applicable procedures.
Welding Inspector Terms & Definitions Section 2 4/23/2007 23 of 691
Welding Terminology & Definitions 2.1 4/23/2007 24 of 691 What is a Weld? • A localised coalescence of metals or non-metals produced either by heating the materials to the welding temperature, with or without the application of pressure, or by the application of pressure alone (AWS) • A permanent union between materials caused by heat, and or pressure (BS499) • An Autogenous weld: A weld made with out the use of a filler material and can only be made by TIG or Oxy-Gas Welding
Welding Terminology & Definitions 2.1 What is a Joint? • The junction of members or the edges of members that are to be joined or have been joined (AWS) • A configuration of members (BS499) 4/23/2007 25 of 691
Joint Terminology 2.2 4/23/2007 26 of 691 Edge Open & Closed Corner Lap Tee Butt Cruciform
Welded Butt Joints 2.2 4/23/2007 27 of 691 A_________Welded butt jointButt A_________Welded butt jointFillet A____________Welded butt jointCompound
4/23/2007 28 of 691 Welded Tee Joints 2.2 A_________Welded T jointFillet A_________Welded T jointButt A____________Welded T jointCompound
Weld Terminology 2.3 4/23/2007 29 of 691 Compound weld Fillet weld Butt weld Edge weld Spot weld Plug weld
Butt Preparations – Sizes 2.4 4/23/2007 30 of 691 Full Penetration Butt Weld Partial Penetration Butt Weld Design Throat Thickness Design Throat Thickness Actual Throat Thickness Actual Throat Thickness
4/23/2007 31 of 691 Weld Zone Terminology 2.5 Weld Boundary C A B D Heat Affected Zone Root Weld metal A, B, C & D = Weld Toes Face
Weld Zone Terminology 2.5 4/23/2007 32 of 691 Excess Root Penetration Excess Cap height or Weld Reinforcement Weld cap width Design Throat Thickness Actual Throat Thickness
Heat Affected Zone (HAZ) 2.5 4/23/2007 33 of 691 tempered zone grain growth zone recrystallised zone partially transformed zone Maximum Temperature solid-liquid Boundarysolid weld metal unaffected base material
Joint Preparation Terminology 2.7 4/23/2007 34 of 691 Included angle Root Gap Root Face Angle of bevel Root Face Root Gap Included angle Root Radius Single-V Butt Single-U Butt
Joint Preparation Terminology 2.8 & 2.9 4/23/2007 35 of 691 Root Gap Root Face Root FaceRoot Gap Root Radius Single Bevel Butt Single-J Butt Angle of bevel Angle of bevel Land
Single Sided Butt Preparations 2.10 4/23/2007 36 of 691 Single Bevel Single Vee Single-J Single-U Single sided preparations are normally made on thinner materials, or when access form both sides is restricted
Double Sided Butt Preparations2.11 4/23/2007 37 of 691 Double sided preparations are normally made on thicker materials, or when access form both sides is unrestricted -VeeDouble-BevelDouble - JDouble - UDouble
Weld Preparation 4/23/2007 38 of 691 Terminology & Typical Dimensions: V-Joints bevel angle root face root gap included angle Typical Dimensions bevel angle 30 to 35° root face ~1.5 to ~2.5mm root gap ~2 to ~4mm
Butt Weld - Toe Blend 4/23/2007 39 of 691 6 mm 80 Poor Weld Toe Blend Angle Improved Weld Toe Blend Angle 20 3 mm •Most codes quote the weld toes shall blend smoothly •This statement is not quantitative and therefore open to individual interpretation •The higher the toe blend angle the greater the amount of stress concentration •The toe blend angle ideally should be between 20o-30o
Fillet Weld Features 2.13 4/23/2007 40 of 691 Design Throat Vertical Leg Length Horizontal leg Length Excess Weld Metal
Fillet Weld Throat Thickness 2.13 4/23/2007 41 of 691 b a b = Actual Throat Thickness a = Design Throat Thickness
Deep Penetration Fillet Weld Features2.13 4/23/2007 42 of 691 b a b = Actual Throat Thickness a = Design Throat Thickness
Fillet Weld Sizes 2.14 Calculating Throat Thickness from a known Leg Length: Design Throat Thickness = Leg Length x 0.7 Question: The Leg length is 14mm. What is the Design Throat? Answer: 14mm x 0.7 = 10mm Throat Thickness 4/23/2007 43 of 691
Fillet Weld Sizes 2.14 Calculating Leg Length from a known Design Throat Thickness: Leg Length = Design Throat Thickness x 1.4 Question: The Design Throat is 10mm. What is the Leg length? Answer: 10mm x 1.4 = 14mm Leg Length 4/23/2007 44 of 691
Features to Consider 2 2.14 Importance of Fillet Weld Leg Length Size 4/23/2007 45 of 691 Approximately the same weld volume in both Fillet Welds, but the effective throat thickness has been altered, reducing considerably the strength of weld B 2mm (b) 4mm 8mm (a) 4mm
Fillet Weld Sizes 2.14 Importance of Fillet weld leg length Size 4/23/2007 46 of 691 Area = 4 x 4 = 8mm2 2 Area = 6 x 6 = 18mm2 2 The c.s.a. of (b) is over double the area of (a) without the extra excess weld metal being added 4mm 6mm (a) (b) 4mm 6mm (a) (b) Excess Excess
4/23/2007 47 of 691 Fillet Weld Profiles 2.15 Mitre Fillet Convex Fillet Concave Fillet A concave profile is preferred for joints subjected to fatigue loading Fillet welds - Shape
EFFECTIVE THROAT THICKNESS 4/23/2007 48 of 691 “s” = Effective throat thickness sa “a” = Nominal throat thickness Deep penetration fillet welds from high heat input welding process MAG, FCAW & SAW etc Fillet Features to Consider 2.15
Welding Positions 2.17 PA 1G / 1F Flat / Downhand PB 2F Horizontal-Vertical PC 2G Horizontal PD 4F Horizontal-Vertical (Overhead) PE 4G Overhead PF 3G / 5G Vertical-Up PG 3G / 5G Vertical-Down H-L045 6G Inclined Pipe (Upwards) J-L045 6G Inclined Pipe (Downwards) 4/23/2007 49 of 691
Welding Positions 2.17 4/23/2007 50 of 691 ISO
Welding position designation2.17 Butt welds in plate (see ISO 6947) 4/23/2007 51 of 691 Flat - PA Overhead - PE Vertical up - PF Vertical down - PG Horizontal - PC
Welding position designation 2.17 Butt welds in pipe (see ISO 6947) 4/23/2007 52 of 691 Flat - PA axis: horizontal pipe: rotated H-L045 axis: inclined at 45° pipe: fixed Horizontal - PC axis: vertical pipe: fixed Vertical up - PF axis: horizontal pipe: fixed Vertical down - PG axis: horizontal pipe: fixed J-L045 axis: inclined at 45° pipe: fixed
Welding position designation2.17 Fillet welds on plate (see ISO 6947) 4/23/2007 53 of 691 Flat - PA Overhead - PD Vertical up - PF Vertical down - PG Horizontal - PB
Welding position designation 2.17 Fillet welds on pipe (see ISO 6947) 4/23/2007 54 of 691 Flat - PA axis: inclined at 45° pipe: rotated Overhead - PD axis: vertical pipe: fixed Vertical up - PF axis: horizontal pipe: fixed Vertical down - PG axis: horizontal pipe: fixed Horizontal - PB axis: vertical pipe: fixed Horizontal - PB axis: horizontal pipe: rotated
4/23/2007 55 of 691 Plate/Fillet Weld Positions2.17 PA / 1G PA / 1F PC / 2G PB / 2F PD / 4F PE / 4G PG / 3G PF / 3G
4/23/2007 56 of 691 Pipe Welding Positions 2.17 Weld: Flat Pipe: rotated Axis: Horizontal PA / 1G Weld: Vertical Downwards Pipe: Fixed Axis: Horizontal PG / 5G Weld: Vertical upwards Pipe: Fixed Axis: Horizontal PF / 5G Weld: Upwards Pipe: Fixed Axis: Inclined Weld: Horizontal Pipe: Fixed Axis: Vertical PC / 2G 45o Weld: Downwards Pipe: Fixed Axis: Inclined J-LO 45 / 6G 45o H-LO 45 / 6G
Travel Speed Measurement2.18 4/23/2007 57 of 691 Definition: the rate of weld progression measured in case of mechanised and automatic welding processes in case of MMA can be determined using ROL and arc time
Welding Inspector Welding Imperfections Section 3 4/23/2007 58 of 691
Welding Imperfections 3.1 4/23/2007 59 of 691 All welds have imperfections • Imperfections are classed as defects when they are of a type, or size, not allowed by the Acceptance Standard A defect is an unacceptable imperfection • A weld imperfection may be allowed by one Acceptance Standard but be classed as a defect by another Standard and require removal/rectification
Welding Imperfections 3.1 4/23/2007 60 of 691 Standards for Welding Imperfections BS EN ISO 6520-1(1998) Welding and allied processes – Classification of geometric imperfections in metallic materials - Part 1: Fusion welding Imperfections are classified into 6 groups, namely: 1 Cracks 2 Cavities 3 Solid inclusions 4 Lack of fusion and penetration 5 Imperfect shape and dimensions 6 Miscellaneous imperfections
Welding Imperfections 3.1 4/23/2007 61 of 691 Standards for Welding Imperfections EN ISO 5817 (2003) Welding - Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) - Quality levels for imperfections This main imperfections given in EN ISO 6520-1 are listed in EN ISO 5817 with acceptance criteria at 3 levels, namely Level B (highest) Level C (intermediate) Level D (general) This Standard is „directly applicable to visual testing of welds‟ ...(weld surfaces & macro examination)
Welding imperfections 3.1 classification Cracks 4/23/2007 62 of 691
Cracks 3.1 Cracks that may occur in welded materials are caused generally by many factors and may be classified by shape and position. Note: Cracks are classed as Planar Defects. 4/23/2007 63 of 691 Classified by Shape •Longitudinal •Transverse •Chevron •Lamellar Tear Classified by Position •HAZ •Centerline •Crater •Fusion zone •Parent metal
Cracks 3.1 4/23/2007 64 of 691 Longitudinal parent metal Longitudinal weld metal Lamellar tearing Transverse weld metal
Cracks 3.1 4/23/2007 65 of 691 Transverse crack Longitudinal crack
Cracks 3.2 Main Crack Types • Solidification Cracks • Hydrogen Induced Cracks • Lamellar Tearing • Reheat cracks 4/23/2007 66 of 691
Cracks 3.2 Solidification Cracking • Occurs during weld solidification process • Steels with high sulphur impurities content (low ductility at elevated temperature) • Requires high tensile stress • Occur longitudinally down centre of weld 4/23/2007 67 of 691
Cracks 3.3 Hydrogen Induced Cold Cracking • Requires susceptible hard grain structure, stress, low temperature and hydrogen • Hydrogen enters weld via welding arc mainly as result of contaminated electrode or preparation • Hydrogen diffuses out into parent metal on cooling • Cracking developing most likely in HAZ 4/23/2007 68 of 691
Lamellar Tearing3.5 • Location: Parent metal • Steel Type: Any steel type possible • Susceptible Microstructure: Poor through thickness ductility • Lamellar tearing has a step like appearance due to the solid inclusions in the parent material (e.g. sulphides and silicates) linking up under the influence of welding stresses • Low ductile materials in the short transverse direction containing high levels of impurities are very susceptible to lamellar tearing • It forms when the welding stresses act in the short transverse direction of the material (through thickness direction) 4/23/2007 69 of 691
Gas Cavities 3.6 4/23/2007 70 of 691 Root piping Cluster porosityGas pore Blow hole Herringbone porosity Gas pore <1.5mm Blow hole.>1.6mm Causes: •Loss of gas shield •Damp electrodes •Contamination •Arc length too large •Damaged electrode flux •Moisture on parent material •Welding current too low
Gas Cavities 3.7 4/23/2007 71 of 691 Root piping Porosity
Gas Cavities 3.8 4/23/2007 72 of 691 Cluster porosity Herringbone porosity
4/23/2007 73 of 691 Crater pipe Weld crater Crater Pipe 3.9
4/23/2007 74 of 691 Crater pipe is a shrinkage defect and not a gas defect, it has the appearance of a gas pore in the weld crater Causes: • Too fast a cooling rate • Deoxidization reactions and liquid to solid volume change • Contamination Crater cracks (Star cracks) Crater pipe Crater Pipe 3.9
Solid Inclusions3.10 Slag inclusions are defined as a non-metallic inclusion caused by some welding process 4/23/2007 75 of 691 Causes: •Slag originates from welding flux •MAG and TIG welding process produce silica inclusions •Slag is caused by inadequate cleaning •Other inclusions include tungsten and copper inclusions from the TIG and MAG welding process Slag inclusions Parallel slag lines Lack of sidewall fusion with associated slag Lack of interun fusion + slag
Solid Inclusions 3.11 4/23/2007 76 of 691 Elongated slag linesInterpass slag inclusions
Welding Imperfections 3.13 4/23/2007 77 of 691 Typical Causes of Lack of Fusion: • welding current too low • bevel angle too steep • root face too large (single-sided weld) • root gap too small (single-sided weld) • incorrect electrode angle • linear misalignment • welding speed too high • welding process related – particularly dip-transfer GMAW • flooding the joint with too much weld metal (blocking Out)
Lack of Fusion3.13 4/23/2007 78 of 691 Incomplete filled groove + Lack of sidewall fusion 1 2 1. Lack of sidewall fusion 2. Lack of inter-run fusion Causes: •Poor welder skill • Incorrect electrode manipulation • Arc blow • Incorrect welding current/voltage • Incorrect travel speed • Incorrect inter-run cleaning
4/23/2007 79 of 691 Lack of sidewall fusion + incomplete filled groove Lack of Fusion 3.13
4/23/2007 80 of 691 Weld Root Imperfections 3.15 Lack of Root Fusion Lack of Root Penetration
4/23/2007 81 of 691 Cap Undercut3.18 Intermittent Cap Undercut
Undercut 3.18 4/23/2007 82 of 691 Cap undercutRoot undercut
Surface and Profile 3.19 4/23/2007 83 of 691 Incomplete filled groove Poor cap profile Excessive cap height Poor cap profiles and excessive cap reinforcements may lead to stress concentration points at the weld toes and will also contribute to overall poor toe blend
Surface and Profile 3.19 4/23/2007 84 of 691 Incomplete filled grooveExcess cap reinforcement
4/23/2007 85 of 691 Excessive root penetration Weld Root Imperfections3.20
Overlap 3.21 4/23/2007 86 of 691 An imperfection at the toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it Causes: •Contamination •Slow travel speed •Incorrect welding technique •Current too low
Overlap 3.21 4/23/2007 87 of 691 Toe Overlap Toe Overlap
Set-Up Irregularities 3.22 4/23/2007 88 of 691 Plate/pipe Linear Misalignment (Hi-Lo) Angular Misalignment Linear misalignment is measured from the lowest plate to the highest point. Angular misalignment is measured in degrees
Set-Up Irregularities3.22 4/23/2007 89 of 691 Linear Misalignment
Set-Up Irregularities3.22 4/23/2007 90 of 691 Linear Misalignment
4/23/2007 91 of 691 Lack of sidewall fusion + incomplete filled groove Incomplete Groove3.23
4/23/2007 92 of 691 Concave Root Causes: • Excessive back purge pressure during TIG welding Excessive root bead grinding before the application of the second pass welding current too high for 2nd pass overhead welding root gap too large - excessive „weaving‟ A shallow groove, which may occur in the root of a butt weld Weld Root Imperfections3.24
4/23/2007 93 of 691 Concave Root Weld Root Imperfections 3.24
Weld Root Imperfections 3.24 4/23/2007 94 of 691 Concave root Excess root penetration
4/23/2007 95 of 691 Causes: • High Amps/volts • Small Root face • Large Root Gap • Slow Travel SpeedBurn through A localized collapse of the weld pool due to excessive penetration resulting in a hole in the root run Weld Root Imperfections 3.25
Weld Root Imperfections3.25 4/23/2007 96 of 691 Burn Through
4/23/2007 97 of 691 Causes: • Loss or insufficient back purging gas (TIG) • Most commonly occurs when welding stainless steels • Purging gases include argon, helium and occasionally nitrogen Oxidized Root (Root Coking)
4/23/2007 98 of 691 Miscellaneous Imperfections 3.26 Arc strike Causes: • Accidental striking of the arc onto the parent material • Faulty electrode holder • Poor cable insulation • Poor return lead clamping
Miscellaneous Imperfections3.27 4/23/2007 99 of 691 Causes: • Excessive current • Damp electrodes • Contamination • Incorrect wire feed speed when welding with the MAG welding process • Arc blowSpatter
Mechanical Damage3.28 Mechanical damage can be defined as any surface material damage cause during the manufacturing process. 4/23/2007 100 of 691 • Grinding • Hammering • Chiselling • Chipping • Breaking off welded attachments (torn surfaces) • Using needle guns to compress weld capping runs
Mechanical Damage 3.28 4/23/2007 101 of 691 Mechanical Damage/Grinding Mark Chipping Marks
Welding Inspector Destructive Testing Section 4 4/23/2007 102 of 691
Qualitative and Quantitative Tests4.1 The following mechanical tests have units and are termed quantitative tests to measure Mechanical Properties • Tensile tests (Transverse Welded Joint, All Weld Metal) • Toughness testing (Charpy, Izod, CTOD) • Hardness tests (Brinell, Rockwell, Vickers) The following mechanical tests have no units and are termed qualitative tests for assessing joint quality • Macro testing • Bend testing • Fillet weld fracture testing • Butt weld nick-break testing 4/23/2007 104 of 691
Mechanical Test Samples 4.1 4/23/2007 105 of 691 Tensile Specimens Fracture Fillet Specimen CTOD Specimen Charpy Specimen Bend Test Specimen
Destructive Testing4.1 4/23/2007 106 of 691 Typical Positions for Test Pieces Specimen Type Position •Macro + Hardness 5 •Transverse Tensile 2, 4 •Bend Tests 2, 4 •Charpy Impact Tests 3 •Additional Tests 3 WELDING PROCEDURE QUALIFICATION TESTING 2 3 4 5 top of fixed pipe
Definitions 4/23/2007 107 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Ability of a material to withstand deformation under static compressive loading without rupture Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions 4/23/2007 108 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Ability of a material undergo plastic deformation under static tensile loading without rupture. Measurable elongation and reduction in cross section area Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions 4/23/2007 109 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Ability of a material to withstand bending or the application of shear stresses by impact loading without fracture. Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions 4/23/2007 110 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Measurement of a materials surface resistance to indentation from another material by static load Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Definitions 4/23/2007 111 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Measurement of the maximum force required to fracture a materials bar of unit cross-sectional area in tension Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
Transverse Joint Tensile Test4.2 Weld on plate 4/23/2007 112 of 691 Multiple cross joint specimensWeld on pipe
Tensile Test 4.3 4/23/2007 113 of 691 All-Weld Metal Tensile Specimen Transverse Tensile Specimen
STRA (Short Transverse Reduction Area) For materials that may be subject to Lamellar Tearing 4/23/2007 114 of 691
UTS Tensile test 4.4 4/23/2007 115 of 691
Charpy V-Notch Impact Test4.5 4/23/2007 116 of 691 Objectives: • measuring impact strength in different weld joint areas • assessing resistance toward brittle fracture Information to be supplied on the test report: • Material type • Notch type • Specimen size • Test temperature • Notch location • Impact Strength Value
Ductile / Brittle Transition Curve4.6 4/23/2007 117 of 691 - 50 0- 20 - 10- 40 - 30 Ductile fracture Ductile/Brittle transition point 47 Joules 28 Joules Testing temperature - Degrees Centigrade Temperature range Transition range Brittle fracture Three specimens are normally tested at each temperature Energy absorbed
Comparison Charpy Impact Test Results4.6 4/23/2007 118 of 691 Impact Energy Joules Room Temperature -20oC Temperature 1. 197 Joules 2. 191 Joules 3. 186 Joules 1. 49 Joules 2. 53 Joules 3. 51 Joules Average = 191 Joules Average = 51 Joules The test results show the specimens carried out at room temperature absorb more energy than the specimens carried out at -20oC
Charpy V-notch impact test specimen4.7 4/23/2007 119 of 691 Specimen dimensions according ASTM E23 ASTM: American Society of Testing Materials
Charpy V-Notch Impact Test 4.8 4/23/2007 120 of 691 Specime n Pendulu m (striker) Anvil (support)
Charpy Impact Test4.9 4/23/2007 121 of 691 10 mm8mm2mm 22.5o Machined notch 100% Ductile Machined notch Large reduction in area, shear lips Fracture surface 100% bright crystalline brittle fracture Randomly torn, dull gray fracture surface 100% Brittle
Hardness Testing4.10 4/23/2007 122 of 691 Definition Measurement of resistance of a material against penetration of an indenter under a constant load There is a direct correlation between UTS and hardness Hardness tests: Brinell Vickers Rockwell
Hardness Testing 4.10 4/23/2007 123 of 691 Objectives: • measuring hardness in different areas of a welded joint • assessing resistance toward brittle fracture, cold cracking and corrosion sensitivity within a H2S (Hydrogen Sulphide) environment. Information to be supplied on the test report: • material type • location of indentation • type of hardness test and load applied on the indenter • hardness value
Vickers Hardness Test 4.11 4/23/2007 124 of 691 Vickers hardness tests: indentation body is a square based diamond pyramid (136º included angle) the average diagonal (d) of the impression is converted to a hardness number from a table it is measured in HV5, HV10 or HV025 Adjustable shuttersIndentationDiamond indentor
Vickers Hardness Test Machine4.11 4/23/2007 125 of 691
Brinell Hardness Test 4.11 4/23/2007 126 of 691 • Hardened steel ball of given diameter is subjected for a given time to a given load • Load divided by area of indentation gives Brinell hardness in kg/mm2 • More suitable for on site hardness testing 30KN Ø=10mm steel ball
Rockwell Hardness Test 4/23/2007 127 of 691 1KN Ø=1.6mm steel ball Rockwell B Rockwell C 1.5KN 120 Diamond Cone
Hardness Testing 4.12 4/23/2007 128 of 691 Hardness Test Methods Typical Designations Vickers 240 HV10 Rockwell Rc 22 Brinell 200 BHN-W usually the hardest region 1.5 to 3mm HAZ fusion line or fusion boundary Hardness specimens can also be used for CTOD samples
Crack Tip Opening Displacement testing 4.12 • Test is for fracture toughness • Square bar machined with a notch placed in the centre. • Tested below ambient temperature at a specified temperature. • Load is applied at either end of the test specimen in an attempt to open a crack at the bottom of the notch • Normally 3 samples 4/23/2007 129 of 691
Fatigue Fracture4.13 4/23/2007 130 of 691 Location: Any stress concentration area Steel Type: All steel types Susceptible Microstructure: All grain structures Test for Fracture Toughness is CTOD (Crack Tip Opening Displacement)
Fatigue Fracture4.13 4/23/2007 131 of 691 • Fatigue cracks occur under cyclic stress conditions • Fracture normally occurs at a change in section, notch and weld defects i.e stress concentration area • All materials are susceptible to fatigue cracking • Fatigue cracking starts at a specific point referred to as a initiation point • The fracture surface is smooth in appearance sometimes displaying beach markings • The final mode of failure may be brittle or ductile or a combination of both
Fatigue Fracture 4/23/2007 132 of 691 • Toe grinding, profile grinding. • The elimination of poor profiles • The elimination of partial penetration welds and weld defects • Operating conditions under the materials endurance limits • The elimination of notch effects e.g. mechanical damage cap/root undercut • The selection of the correct material for the service conditions of the component Precautions against Fatigue Cracks
Fatigue Fracture Fatigue fracture occurs in structures subject to repeated application of tensile stress. Crack growth is slow (in same cases, crack may grow into an area of low stress and stop without failure). 4/23/2007 133 of 691
Fatigue Fracture 4/23/2007 134 of 691 Initiation points / weld defects Fatigue fracture surface smooth in appearance Secondary mode of failure ductile fracture rough fibrous appearance
Fatigue Fracture • Crack growth is slow • It initiate from stress concentration points • load is considerably below the design or yield stress level • The surface is smooth • The surface is bounded by a curve • Bands may sometimes be seen on the smooth surface –”beachmarks”. They show the progress of the crack front from the point of origin • The surface is 90° to the load • Final fracture will usually take the form of gross yielding (as the maximum stress in the remaining ligament increase!) • Fatigue crack need initiation + propagation periods 4/23/2007 135 of 691 Fatigue fracture distinguish features:
Bend Tests 4.15 4/23/2007 136 of 691 Object of test: • To determine the soundness of the weld zone. Bend testing can also be used to give an assessment of weld zone ductility. • There are three ways to perform a bend test: Root bend Face bend Side bend Side bend tests are normally carried out on welds over 12mm in thickness
Bending test4.16 Types of bend test for welds (acc. BS EN 910): 4/23/2007 137 of 691 Thickness of material - “t” “t” up to 12 mm “t” over 12 mm Root / face bend Side bend
Fillet Weld Fracture Tests 4.17 Object of test: • To break open the joint through the weld to permit examination of the fracture surfaces • Specimens are cut to the required length • A saw cut approximately 2mm in depth is applied along the fillet welds length • Fracture is usually made by striking the specimen with a single hammer blow • Visual inspection for defects 4/23/2007 138 of 691
Fillet Weld Fracture Tests4.17 4/23/2007 139 of 691 Fracture should break weld saw cut to root 2mm Notch Hammer
Fillet Weld Fracture Tests 4.17 4/23/2007 140 of 691 This fracture indicates lack of fusion This fracture has occurred saw cut to root Lack of Penetration
Nick-Break Test4.18 Object of test: • To permit evaluation of any weld defects across the fracture surface of a butt weld. •Specimens are cut transverse to the weld •A saw cut approximately 2mm in depth is applied along the welds root and cap •Fracture is usually made by striking the specimen with a single hammer blow •Visual inspection for defects 4/23/2007 141 of 691
Nick-Break Test4.18 4/23/2007 142 of 691 Approximately 230 mm 19 mm 2 mm 2 mm Notch cut by hacksaw Weld reinforcement may or may not be removed
Nick Break Test 4.18 4/23/2007 143 of 691 Inclusions on fracture line Lack of root penetration or fusion Alternative nick-break test specimen, notch applied all way around the specimen
4/23/2007 144 of 691 We test welds to establish minimum levels of mechanical properties, and soundness of the welded joint We divide tests into Qualitative & Quantitative methods: Qualitative: (Have no units/numbers) For assessing joint quality Macro tests Bend tests Fillet weld fracture tests Butt Nick break tests Quantitative: (Have units/numbers) To measure mechanical properties Hardness (VPN & BHN) Toughness (Joules & ft.lbs) Strength (N/mm2 & PSI, MPa) Ductility / Elongation (E%) Summary of Mechanical Testing4.19
Welding Inspector WPS – Welder Qualifications Section 5 4/23/2007 145 of 691
4/23/2007 146 of 691 Welding Procedure Qualification5.1 Question: What is the main reason for carrying out a Welding Procedure Qualification Test ? (What is the test trying to show ?) Answer: To show that the welded joint has the properties* that satisfy the design requirements (fit for purpose) * properties •mechanical properties are the main interest - always strength but toughness & hardness may be important for some applications •test also demonstrates that the weld can be made without defects
Welding Procedures5.1 4/23/2007 147 of 691 Producing a welding procedure involves: • Planning the tasks • Collecting the data • Writing a procedure for use of for trial • Making a test welds • Evaluating the results • Approving the procedure • Preparing the documentation
Welding Procedures 5.2 4/23/2007 148 of 691 In most codes reference is made to how the procedure are to be devised and whether approval of these procedures is required. The approach used for procedure approval depends on the code: Example codes: • AWS D.1.1: Structural Steel Welding Code • BS 2633: Class 1 welding of Steel Pipe Work • API 1104: Welding of Pipelines • BS 4515: Welding of Pipelines over 7 Bar Other codes may not specifically deal with the requirement of a procedure but may contain information that may be used in writing a weld procedure • EN 1011Process of Arc Welding Steels
4/23/2007 149 of 691 The welding engineer writes qualified Welding Procedure Specifications (WPS) for production welding Welding Procedure Qualification 5.3 Production welding conditions must remain within the range of qualification allowed by the WPQR (according to EN ISO 15614)
4/23/2007 150 of 691 Welding Procedure Qualification5.3 (according to EN Standards) welding conditions are called welding variables welding variables are classified by the EN ISO Standard as: •Essential variables •Non-essential variables •Additional variables Note: additional variables = ASME supplementary essential The range of qualification for production welding is based on the limits that the EN ISO Standard specifies for essential variables* (* and when applicable - the additional variables)
4/23/2007 151 of 691 Welding Procedure Qualification5.3 (according to EN Standards) WELDING ESSENTIAL VARIABLES Question: Why are some welding variables classified as essential ? Answer: A variable, that if changed beyond certain limits (specified by the Welding Standard) may have a significant effect on the properties* of the joint * particularly joint strength and ductility
4/23/2007 152 of 691 Welding Procedure Qualification5.3 (according to EN Standards) SOME TYPICAL ESSENTIAL VARIABLES • Welding Process • Post Weld Heat Treatment (PWHT) • Material Type • Electrode Type, Filler Wire Type (Classification) • Material Thickness • Polarity (AC, DC+ve / DC-ve) • Pre-Heat Temperature • Heat Input • Welding Position
Welding Procedures5.3 Components of a welding procedure Parent material • Type (Grouping) • Thickness • Diameter (Pipes) • Surface condition) Welding process • Type of process (MMA, MAG, TIG, SAW etc) • Equipment parameters • Amps, Volts, Travel speed Welding Consumables • Type of consumable/diameter of consumable • Brand/classification • Heat treatments/ storage 4/23/2007 153 of 691
Welding Procedures5.3 Components of a welding procedure Joint design •Edge preparation •Root gap, root face •Jigging and tacking •Type of baking Welding Position •Location, shop or site •Welding position e.g. 1G, 2G, 3G etc •Any weather precaution Thermal heat treatments •Preheat, temps •Post weld heat treatments e.g. stress relieving 4/23/2007 154 of 691
Welding Procedures5.3 4/23/2007 155 of 691 Object of a welding procedure test To give maximum confidence that the welds mechanical and metallurgical properties meet the requirements of the applicable code/specification. Each welding procedure will show a range to which the procedure is approved (extent of approval) If a customer queries the approval evidence can be supplied to prove its validity
Welding Procedures 4/23/2007 156 of 691 Summary of designations: pWPS: Preliminary Welding Procedure Specification (Before procedure approval) WPAR (WPQR): Welding Procedure Approval Record (Welding procedure Qualification record) WPS: Welding Procedure Specification (After procedure approval)
4/23/2007 157 of 691 Example: Welding Procedure Specification (WPS)
Welder Qualification5.4 4/23/2007 158 of 691 Numerous codes and standards deal with welder qualification, e.g. BS EN 287. • Once the content of the procedure is approved the next stage is to approve the welders to the approved procedure. • A welders test know as a Welders Qualification Test (WQT). Object of a welding qualification test: • To give maximum confidence that the welder meets the quality requirements of the approved procedure (WPS). • The test weld should be carried out on the same material and same conditions as for the production welds.
4/23/2007 159 of 691 Welder Qualification 5.4 & 5.5 (according to EN Standards) Question: What is the main reason for qualifying a welder ? Answer: To show that he has the skill to be able to make production welds that are free from defects Note: when welding in accordance with a Qualified WPS
4/23/2007 160 of 691 The welder is allowed to make production welds within the range of qualification shown on the Certificate The range of qualification allowed for production welding is based on the limits that the EN Standard specifies for the welder qualification essential variables Welder Qualification 5.5 (according to EN 287 ) A Certificate may be withdrawn by the Employer if there is reason to doubt the ability of the welder, for example • a high repair rate • not working in accordance with a qualified WPS The qualification shall remain valid for 2 years provided there is certified confirmation of welding to the WPS in that time. A Welder‟s Qualification Certificate automatically expires if the welder has not used the welding process for 6 months or longer.
4/23/2007 161 of 691 Welding Engineer writes a preliminary Welding Procedure Specification (pWPS) for each test weld to be made • A welder makes a test weld in accordance with the pWPS • A welding inspector records all the welding conditions used for the test weld (referred to as the „as-run‟ conditions) An Independent Examiner/ Examining Body/ Third Party inspector may be requested to monitor the qualification process Welding Procedure Qualification5.7 (according to EN ISO 15614) The finished test weld is subjected to NDT in accordance with the methods specified by the EN ISO Standard - Visual, MT or PT & RT or UT
4/23/2007 162 of 691 Welding Procedure Qualification 5.7 Test weld is subjected to destructive testing (tensile, bend, macro) The Application Standard, or Client, may require additional tests such as impact tests, hardness tests (and for some materials - corrosion tests) (according to EN ISO 15614) A Welding Procedure Qualification Record (WPQR) is prepared giving details of: - • The welding conditions used for the test weld • Results of the NDT • Results of the destructive tests • The welding conditions that the test weld allows for production welding The Third Party may be requested to sign the WPQR as a true record
Welder Qualification5.9 4/23/2007 163 of 691 (according to EN 287 ) An approved WPS should be available covering the range of qualification required for the welder approval. • The welder qualifies in accordance with an approved WPS • A welding inspector monitors the welding to make sure that the welder uses the conditions specified by the WPS EN Welding Standard states that an Independent Examiner, Examining Body or Third Party Inspector may be required to monitor the qualification process
4/23/2007 164 of 691 The finished test weld is subjected to NDT by the methods specified by the EN Standard - Visual, MT or PT & RT or UT The test weld may need to be destructively tested - for certain materials and/or welding processes specified by the EN Standard or the Client Specification Welder Qualification5.9 (according to EN 287 ) • A Welder‟s Qualification Certificate is prepared showing the conditions used for the test weld and the range of qualification allowed by the EN Standard for production welding • The Qualification Certificate is usually endorsed by a Third Party Inspector as a true record of the test
Welder Qualification5.10 4/23/2007 165 of 691 Information that should be included on a welders test certificate are, which the welder should have or have access to a copy of ! • Welders name and identification number • Date of test and expiry date of certificate • Standard/code e.g. BS EN 287 • Test piece details • Welding process. • Welding parameters, amps, volts • Consumables, flux type and filler classification details • Sketch of run sequence • Welding positions • Joint configuration details • Material type qualified, pipe diameter etc • Test results, remarks • Test location and witnessed by • Extent (range) of approval
Welding Inspector Materials Inspection Section 6 4/23/2007 167 of 691
Material Inspection One of the most important items to consider is Traceability. The materials are of little use if we can not, by use of an effective QA system trace them from specification and purchase order to final documentation package handed over to the Client. All materials arriving on site should be inspected for: • Size / dimensions • Condition • Type / specification In addition other elements may need to be considered depending on the materials form or shape 4/23/2007 168 of 691
Pipe Inspection 4/23/2007 169 of 691 We inspect the condition (Corrosion, Damage, Wall thickness Ovality, Laminations & Seam) Specification Welded seam Size LP5 Other checks may need to be made such as: distortion tolerance, number of plates and storage.
Plate Inspection 4/23/2007 170 of 691 Size We inspect the condition (Corrosion, Mechanical damage, Laps, Bands & Laminations) 5L Specification Other checks may need to be made such as: distortion tolerance, number of plates and storage.
4/23/2007 171 of 691 Parent Material Imperfections Lamination Mechanical damage Lap Segregation line Laminations are caused in the parent plate by the steel making process, originating from ingot casting defects. Segregation bands occur in the centre of the plate and are low melting point impurities such as sulphur and phosphorous. Laps are caused during rolling when overlapping metal does not fuse to the base material.
Lapping 4/23/2007 172 of 691
Lamination 4/23/2007 173 of 691
4/23/2007 174 of 691 Laminations Plate Lamination
Welding Inspector Codes & Standards Section 7 4/23/2007 175 of 691
Codes & Standards 4/23/2007 176 of 691 The 3 agencies generally identified in a code or standard: The customer, or client The manufacturer, or contractor The 3rd party inspection, or clients representative Codes often do not contain all relevant data, but may refer to other standards
4/23/2007 177 of 691 Standard/Codes/Specifications STANDARDS SPECIFICATIONS CODES Examples plate, pipe forgings, castings valves electrodes Examples pressure vessels bridges pipelines tanks
Welding Inspector Welding Symbols Section 8 4/23/2007 178 of 691
Weld symbols on drawings Advantages of symbolic representation: • simple and quick plotting on the drawing • does not over-burden the drawing • no need for additional view • gives all necessary indications regarding the specific joint to be obtained Disadvantages of symbolic representation: • used only for usual joints • requires training for properly understanding of symbols 4/23/2007 179 of 691
Weld symbols on drawings The symbolic representation includes: • an arrow line • a reference line • an elementary symbol The elementary symbol may be completed by: • a supplementary symbol • a means of showing dimensions • some complementary indications 4/23/2007 180 of 691
Dimensions 4/23/2007 181 of 691 In most standards the cross sectional dimensions are given to the left side of the symbol, and all linear dimensions are give on the right side Convention of dimensions a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length (min material thickness) BS EN ISO 22553 AWS A2.4 •In a fillet weld, the size of the weld is the leg length •In a butt weld, the size of the weld is based on the depth of the joint preparation
4/23/2007 182 of 691 A method of transferring information from the design office to the workshop is: The above information does not tell us much about the wishes of the designer. We obviously need some sort of code which would be understood by everyone. Most countries have their own standards for symbols. Some of them are AWS A2.4 & BS EN 22553 (ISO 2553) Please weld here Weld symbols on drawings
4/23/2007 183 of 691 Joints in drawings may be indicated: •by detailed sketches, showing every dimension •by symbolic representation Weld symbols on drawings
Elementary Welding Symbols (BS EN ISO 22553 & AWS A2.4) Convention of the elementary symbols: Various categories of joints are characterised by an elementary symbol. The vertical line in the symbols for a fillet weld, single/double bevel butts and a J-butt welds must always be on the left side. 4/23/2007 184 of 691 Square edge butt weld Weld type Sketch Symbol Single-v butt weld
Elementary Welding Symbols 4/23/2007 185 of 691 Single-V butt weld with broad root face Weld type Sketch Symbol Single bevel butt weld Single bevel butt weld with broad root face Backing run
Elementary Welding Symbols 4/23/2007 186 of 691 Single-U butt weld Weld type Sketch Symbol Single-J butt weld Fillet weld Surfacing
ISO 2553 / BS EN 22553 4/23/2007 187 of 691 Plug weld Resistance spot weld Resistance seam weld Square Butt weld Steep flanked Single-V Butt Surfacing
4/23/2007 188 of 691 Arrow Line (BS EN ISO 22553 & AWS A2.4): Convention of the arrow line: • Shall touch the joint intersection • Shall not be parallel to the drawing • Shall point towards a single plate preparation (when only one plate has preparation)
4/23/2007 189 of 691 (AWS A2.4) Convention of the reference line: Shall touch the arrow line Shall be parallel to the bottom of the drawing Reference Line
4/23/2007 190 of 691 or Reference Line (BS EN ISO 22553) Convention of the reference line: • Shall touch the arrow line • Shall be parallel to the bottom of the drawing • There shall be a further broken identification line above or beneath the reference line (Not necessary where the weld is symmetrical!)
4/23/2007 191 of 691 (BS EN ISO 22553 & AWS A2.4) Convention of the double side weld symbols: Representation of welds done from both sides of the joint intersection, touched by the arrow head Fillet weld Double V Double bevel Double U Double J Double side weld symbols
ISO 2553 / BS EN 22553 4/23/2007 192 of 691 Arrow line Reference lines Arrow side Other side Arrow side Other side
ISO 2553 / BS EN 22553 4/23/2007 193 of 691 Single-V Butt flush cap Single-U Butt with sealing run Single-V Butt with permanent backing strip M Single-U Butt with removable backing strip M R
ISO 2553 / BS EN 22553 4/23/2007 194 of 691 Single-bevel butt Double-bevel butt Single-bevel butt Single-J butt
ISO 2553 / BS EN 22553 4/23/2007 195 of 691 Partial penetration single-V butt „S‟ indicates the depth of penetration s10 10 15
ISO 2553 / BS EN 22553 4/23/2007 196 of 691 a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length(min material thickness) a = (0.7 x z) a 4 4mm Design throat z 6 6mm leg a z s s 6 6mm Actual throat
ISO 2553 / BS EN 22553 4/23/2007 197 of 691 Arrow side Arrow side
ISO 2553 / BS EN 22553 4/23/2007 198 of 691 Other side Other side s6 s6 6mm fillet weld
ISO 2553 / BS EN 22553 4/23/2007 199 of 691 n = number of weld elements l = length of each weld element (e) = distance between each weld element n x l (e) Welds to be staggered Process 2 x 40 (50) 3 x 40 (50) 111
ISO 2553 / BS EN 22553 4/23/2007 200 of 691 80 80 80 909090 6 6 5 5 z5 z6 3 x 80 (90) 3 x 80 (90) All dimensions in mm
ISO 2553 / BS EN 22553 4/23/2007 201 of 691 All dimensions in mm 8 8 6 6 80 80 80 909090 z8 z6 3 x 80 (90) 3 x 80 (90)
4/23/2007 202 of 691 Supplementary symbols Concave or Convex Toes to be ground smoothly (BS EN only) Site Weld Weld all round (BS EN ISO 22553 & AWS A2.4) Convention of supplementary symbols Supplementary information such as welding process, weld profile, NDT and any special instructions
4/23/2007 203 of 691 Supplementary symbols Further supplementary information, such as WPS number, or NDT may be placed in the fish tail Ground flush 111 Welding process numerical BS EN MR Removable backing strip Permanent backing strip M (BS EN ISO 22553 & AWS A2.4) Convention of supplementary symbols Supplementary information such as welding process, weld profile, NDT and any special instructions
ISO 2553 / BS EN 22553 4/23/2007 204 of 691 ba dc
ISO 2553 / BS EN 22553 4/23/2007 205 of 691 ConvexMitre Toes shall be blended Concave
ISO 2553 / BS EN 22553 4/23/2007 206 of 691 a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length(min material thickness) a = (0.7 x z) a 4 4mm Design throat z 6 6mm leg a z s s 6 6mm Actual throat
ISO 2553 / BS EN 22553 Complimentary Symbols 4/23/2007 207 of 691 Field weld (site weld) The component requires NDT inspection WPS Additional information, the reference document is included in the box Welding to be carried out all round component (peripheral weld) NDT
ISO 2553 / BS EN 22553 4/23/2007 208 of 691 Numerical Values for Welding Processes: 111: MMA welding with covered electrode 121: Sub-arc welding with wire electrode 131: MIG welding with inert gas shield 135: MAG welding with non-inert gas shield 136: Flux core arc welding 141: TIG welding 311: Oxy-acetylene welding 72: Electro-slag welding 15: Plasma arc welding
AWS A2.4 Welding Symbols 4/23/2007 209 of 691
AWS Welding Symbols 4/23/2007 210 of 691 1(1-1/8) 60o 1/8 Depth of Bevel Effective Throat Root Opening Groove Angle
AWS Welding Symbols 4/23/2007 211 of 691 1(1-1/8) 60o 1/8 GSFCAW Welding Process GMAW GTAW SAW
AWS Welding Symbols 4/23/2007 212 of 691 3 – 10 3 – 10 Welds to be staggered SMAW Process 10 3 3
AWS Welding Symbols 4/23/2007 213 of 691 1(1-1/8) 60o 1/8 FCAW Sequence of Operations 1st Operation 2nd Operation 3rd Operation
AWS Welding Symbols 4/23/2007 214 of 691 1(1-1/8) 60o 1/8 FCAW Sequence of Operations RT MT MT
AWS Welding Symbols 4/23/2007 215 of 691 Dimensions- Leg Length 6/8 6 leg on member A 8 6Member A Member B
Welding Inspector Intro To Welding Processes Section 9 4/23/2007 221 of 691
Welding Processes 4/23/2007 222 of 691 Welding is regarded as a joining process in which the work pieces are in atomic contact Pressure welding • Forge welding • Friction welding • Resistance Welding Fusion welding • Oxy-acetylene • MMA (SMAW) • MIG/MAG (GMAW) • TIG (GTAW) • Sub-arc (SAW) • Electro-slag (ESW) • Laser Beam (LBW) • Electron-Beam (EBW)
4/23/2007 225 of 691 20 8040 60 130 140120100 180160 200 10 60 50 40 30 20 80 70 90 100 Normal Operating Voltage Range Large voltage variation, e.g. + 10v (due to changes in arc length) Small amperage change resulting in virtually constant current e.g. + 5A. Voltage Amperage Required for: MMA, TIG, Plasma arc and SAW > 1000 AMPS O.C.V. Striking voltage (typical) for arc initiation Constant Current Power Source (Drooping Characteristic)
Monitoring Heat Input • Heat Input: The amount of heat generated in the welding arc per unit length of weld. Expressed in kilo Joules per millimetre length of weld (kJ/mm). Heat Input (kJ/mm)= Volts x Amps Travel speed(mm/s) x 1000 4/23/2007 227 of 691
Monitoring Heat Input 4/23/2007 228 of 691 Weld and weld pool temperatures
Monitoring Heat Input 4/23/2007 229 of 691
Monitoring Heat Input • Monitoring Heat Input As Required by • BS EN ISO 15614-1:2004 • In accordance with EN 1011-1:1998 4/23/2007 230 of 691 When impact requirements and/or hardness requirements are specified, impact test shall be taken from the weld in the highest heat input position and hardness tests shall be taken from the weld in the lowest heat input position in order to qualify for all positions
Welding Inspector MMA Welding Section 10 4/23/2007 231 of 691
MMA - Principle of operation 4/23/2007 233 of 691
MMA welding Main features: • Shielding provided by decomposition of flux covering • Electrode consumable • Manual process Welder controls: • Arc length • Angle of electrode • Speed of travel • Amperage settings 4/23/2007 234 of 691
Manual Metal Arc Basic Equipment 4/23/2007 235 of 691 Power source Holding oven Inverter power source Electrode holder Power cables Welding visor filter glass Return lead Electrodes Electrode oven Control panel (amps, volts)
MMA Welding Plant 4/23/2007 236 of 691 Transformer: • Changes mains supply voltage to a voltage suitable for welding. Has no moving parts and is often termed static plant. Rectifier: • Changes a.c. to d.c., can be mechanically or statically achieved. Generator: • Produces welding current. The generator consists of an armature rotating in a magnetic field, the armature must be rotated at a constant speed either by a motor unit or, in the absence of electrical power, by an internal combustion engine. Inverter: • An inverter changes d.c. to a.c. at a higher frequency.
MMA Welding Variables 4/23/2007 237 of 691 Voltage • The arc voltage in the MMA process is measured as close to the arc as possible. It is variable with a change in arc length O.C.V. • The open circuit voltage is the voltage required to initiate, or re-ignite the electrical arc and will change with the type of electrode being used e.g 70-90 volts Current • The current used will be determined by the choice of electrode, electrode diameter and material type and thickness. Current has the most effect on penetration. Polarity • Polarity is generally determined by operation and electrode type e.g DC +ve, DC –ve or AC
4/23/2007 239 of 691 20 8040 60 130 140120100 180160 200 10 60 50 40 30 20 80 70 90 100 Normal Operating Voltage Range Large voltage variation, e.g. + 10v (due to changes in arc length) Small amperage change resulting in virtually constant current e.g. + 5A. Voltage Amperage O.C.V. Striking voltage (typical) for arc initiation Constant Current Power Source (Drooping Characteristic)
MMA welding parameters Travel speed 4/23/2007 240 of 691 Travel speed Too highToo low •wide weld bead contour •lack of penetration •burn-through •lack of root fusion •incomplete root penetration •undercut •poor bead profile, difficult slag removal
MMA welding parameters Type of current: • voltage drop in welding cables is lower with AC • inductive looses can appear with AC if cables are coiled • cheaper power source for AC • no problems with arc blow with AC • DC provides a more stable and easy to strike arc, especially with low current, better positional weld, thin sheet applications • welding with a short arc length (low arc voltage) is easier with DC, better mechanical properties • DC provides a smoother metal transfer, less spatter 4/23/2007 241 of 691
MMA welding parameters Welding current 4/23/2007 242 of 691 – approx. 35 A/mm of diameter – governed by thickness, type of joint and welding position Welding current Too highToo low •poor starting •slag inclusions •weld bead contour too high •lack of fusion/penetration •spatter •excess penetration •undercut •burn-through
MMA welding parameters Arc length = arc voltage 4/23/2007 243 of 691 Arc voltage Too highToo low •arc can be extinguished •“stubbing” •spatter •porosity •excess penetration •undercut •burn-through Polarity: DCEP generally gives deeper penetration
MMA - Troubleshooting 4/23/2007 244 of 691 MMA quality (left to right) current, arc length and travel speed normal; current too low; current too high; arc length too short; arc length too long; travel speed too slow; travel speed too high
MMA electrode holder 4/23/2007 245 of 691 Collet or twist type “Tongs” type with spring-loaded jaws
MMA Welding Consumables 4/23/2007 246 of 691 The three main electrode covering types used in MMA welding • Cellulosic - deep penetration/fusion • Rutile - general purpose • Basic - low hydrogen (Covered in more detail in Section 14) MMA Covered Electrodes
4/23/2007 247 of 691 Most welding defects in MMA are caused by a lack of welder skill (not an easily controlled process), the incorrect settings of the equipment, or the incorrect use, and treatment of electrodes Typical Welding Defects: •Slag inclusions •Arc strikes •Porosity •Undercut •Shape defects (overlap, excessive root penetration, etc.) MMA welding typical defects
Manual Metal Arc Welding (MMA) 4/23/2007 248 of 691 Advantages: • Field or shop use • Range of consumables • All positions • Portable • Simple equipment Disadvantages: • High welder skill required • High levels of fume • Hydrogen control (flux) • Stop/start problems • Comparatively uneconomic when compared with some other processes i.e MAG, SAW and FCAW
Welding Inspector TIG Welding Section 11 4/23/2007 249 of 691
Tungsten Inert Gas Welding 4/23/2007 250 of 691 The TIG welding process was first developed in the USA during the 2nd world war for the welding of aluminum alloys • The process uses a non-consumable tungsten electrode • The process requires a high level of welder skill • The process produces very high quality welds. • The TIG process is considered as a slow process compared to other arc welding processes • The arc may be initiated by a high frequency to avoid scratch starting, which could cause contamination of the tungsten and weld
TIG - Principle of operation 4/23/2007 251 of 691
TIG Welding Variables 4/23/2007 254 of 691 Voltage The voltage of the TIG welding process is variable only by the type of gas being used, and changes in the arc length Current The current is adjusted proportionally to the tungsten electrodes diameter being used. The higher the current the deeper the penetration and fusion Polarity The polarity used for steels is always DC –ve as most of the heat is concentrated at the +ve pole, this is required to keep the tungsten electrode at the cool end of the arc. When welding aluminium and its alloys AC current is used
Types of current • can be DCEN or DCEP • DCEN gives deep penetration • requires special power source • low frequency - up to 20 pulses/sec (thermal pulsing) • better weld pool control • weld pool partially solidifies between pulses4/23/2007 256 of 691 Type of welding current can be sine or square wave requires a HF current (continuos or periodical) provide cleaning action DC AC Pulsed current
Choosing the proper electrode Current type influence 4/23/2007 257 of 691 + + + + + + + + + - - - - - - - - - Electrode capacity Current type & polarity Heat balance Oxide cleaning action Penetration DCEN DCEPAC (balanced) 70% at work 30% at electrode 50% at work 50% at electrode 35% at work 65% at electrode Deep, narrow Medium Shallow, wide No Yes - every half cycle Yes Excellent (e.g. 3,2 mm/400A) Good (e.g. 3,2 mm/225A) Poor (e.g. 6,4 mm/120A)
ARC CHARACTERISTICS 4/23/2007 258 of 691 Volts Amps OCV Constant Current/Amperage Characteristic Large change in voltage = Smaller change in amperage Welding Voltage Large arc gap Small arc gap
TIG - arc initiation methods • simple method • tungsten electrode is in contact with the workpiece! • high initial arc current due to the short circuit • impractical to set arc length in advance • electrode should tap the workpiece - no scratch! • ineffective in case of AC • used when a high quality is not essential 4/23/2007 259 of 691 Arc initiation method Lift arc HF start need a HF generator (spark- gap oscillator) that generates a high voltage AC output (radio frequency) costly reliable method required on both DC (for start) and AC (to re-ignite the arc) can be used remotely HF produce interference requires superior insulation
Pulsed current • usually peak current is 2-10 times background current • useful on metals sensitive to high heat input • reduced distortions • in case of dissimilar thicknesses equal penetration can be achieved 4/23/2007 260 of 691 Time Current(A) Pulse time Cycle time Peak current Background current Average current one set of variables can be used in all positions used for bridging gaps in open root joints require special power source
Choosing the proper electrode Polarity Influence – cathodic cleaning effect 4/23/2007 261 of 691
Tungsten Electrodes 4/23/2007 262 of 691 Old types: (Slightly Radioactive) • Thoriated: DC electrode -ve - steels and most metals • 1% thoriated + tungsten for higher current values • 2% thoriated for lower current values • Zirconiated: AC - aluminum alloys and magnesium New types: (Not Radioactive) • Cerium: DC electrode -ve - steels and most metals • Lanthanum: AC - Aluminum alloys and magnesium
TIG torch set-up • Electrode extension 4/23/2007 263 of 691 Electrode extension Stickout 2-3 times electrode diameter Electrode extension Low electron emission Unstable arc Too small Overheating Tungsten inclusions Too large
Choosing the correct electrode Polarity Influence – cathodic cleaning effect 4/23/2007 264 of 691
Tungsten Electrodes 4/23/2007 265 of 691 Old types: (Slightly Radioactive) • Thoriated: DC electrode -ve - steels and most metals • 1% thoriated + tungsten for higher current values • 2% thoriated for lower current values • Zirconiated: AC - aluminum alloys and magnesium New types: (Not Radioactive) • Cerium: DC electrode -ve - steels and most metals • Lanthanum: AC - Aluminum alloys and magnesium
Tungsten electrode types 4/23/2007 266 of 691 Pure tungsten electrodes: colour code - green no alloy additions low current carrying capacity maintains a clean balled end can be used for AC welding of Al and Mg alloys poor arc initiation and arc stability with AC compared with other electrode types used on less critical applications low cost
Tungsten electrode types 4/23/2007 267 of 691 Thoriated tungsten electrodes: colour code - yellow/red/violet 20% higher current carrying capacity compared to pure tungsten electrodes longer life - greater resistance to contamination thermionic - easy arc initiation, more stable arc maintain a sharpened tip recommended for DCEN, seldom used on AC (difficult to maintain a balled tip) This slightly radioactive
Tungsten electrode types 4/23/2007 268 of 691 Ceriated tungsten electrodes: colour code - grey (orange acc. AWS A-5.12) operate successfully with AC or DC Ce not radioactive - replacement for thoriated types Lanthaniated tungsten electrodes: colour code - black/gold/blue operating characteristics similar with ceriated electrode
Tungsten electrode types 4/23/2007 269 of 691 Zirconiated tungsten electrodes: colour code - brown/white operating characteristics fall between those of pure and thoriated electrodes retains a balled end during welding - good for AC welding high resistance to contamination preferred for radiographic quality welds
Electrode tip for DCEN 4/23/2007 270 of 691 Electrode tip prepared for low current welding Electrode tip prepared for high current welding Vertex angle Penetration increase Increase Bead width increase Decrease 2-2,5times electrodediameter
Electrode tip for AC 4/23/2007 271 of 691 Electrode tip ground Electrode tip ground and then conditioned DC -ve AC
TIG Welding Variables 4/23/2007 272 of 691 Tungsten electrodes The electrode diameter, type and vertex angle are all critical factors considered as essential variables. The vertex angle is as shown Vetex angle Note: when welding aluminium with AC current, the tungsten end is chamfered and forms a ball end when welding DC -ve Note: too fine an angle will promote melting of the electrodes tip AC
Choosing the proper electrode 4/23/2007 273 of 691 Unstable arc Tungsten inclusions Welding current Electrode tip not properly heated Excessive melting or volatilisation Too low Too high Factors to be considered: Penetration
Shielding gas requirements • Preflow and postflow 4/23/2007 275 of 691 Preflow Postflow Shielding gas flow Welding current Flow rate too low Flow rate too high
Special shielding methods 4/23/2007 276 of 691 Pipe root run shielding – Back Purging to prevent excessive oxidation during welding, normally argon.
TIG torch set-up Electrode extension 4/23/2007 277 of 691 Electrode extension Stickout 2-3 times electrode diameter Electrode extension Low electron emission Unstable arc Too small Overheating Tungsten inclusions Too large
TIG Welding Consumables Welding consumables for TIG: •Filler wires, Shielding gases, tungsten electrodes (non- consumable). •Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification •Steel Filler wires of very high quality, with copper coating to resist corrosion. •shielding gases mainly Argon and Helium, usually of highest purity (99.9%). 4/23/2007 278 of 691
Tungsten Inclusion 4/23/2007 279 of 691 A Tungsten Inclusion always shows up as bright white on a radiograph May be caused by Thermal Shock of heating to fast and small fragments break off and enter the weld pool, so a “slope up” device is normally fitted to prevent this could be caused by touch down also. Most TIG sets these days have slope- up devices that brings the current to the set level over a short period of time so the tungsten is heated more slowly and gently
4/23/2007 280 of 691 Most welding defects with TIG are caused by a lack of welder skill, or incorrect setting of the equipment. i.e. current, torch manipulation, welding speed, gas flow rate, etc. • Tungsten inclusions (low skill or wrong vertex angle) • Surface porosity (loss of gas shield mainly on site) • Crater pipes (bad weld finish technique i.e. slope out) • Oxidation of S/S weld bead, or root by poor gas cover • Root concavity (excess purge pressure in pipe) • Lack of penetration/fusion (widely on root runs) TIG typical defects
Tungsten Inert Gas Welding Advantages • High quality • Good control • All positions • Lowest H2 process • Minimal cleaning • Autogenous welding (No filler material) • Can be automated Disadvantages • High skill factor required • Low deposition rate • Small consumable range • High protection required • Complex equipment • Low productivity • High ozone levels +HF 4/23/2007 281 of 691
Welding Inspector MIG/MAG Welding Section 12 4/23/2007 282 of 691
Gas Metal Arc Welding 4/23/2007 283 of 691 The MIG/MAG welding process was initially developed in the USA in the late 1940s for the welding of aluminum alloys. The latest EN Welding Standards now refer the process by the American term GMAW (Gas Metal Arc Welding) • The process uses a continuously fed wire electrode • The weld pool is protected by a separately supplied shielding gas • The process is classified as a semi-automatic welding process but may be fully automated • The wire electrode can be either bare/solid wire or flux cored hollow wire
MIG/MAG - Principle of operation 4/23/2007 284 of 691
MIG/MAG process variables • Welding current • Polarity 4/23/2007 286 of 691 •Increasing welding current •Increase in depth and width •Increase in deposition rate
MIG/MAG process variables • Arc voltage • Travel speed 4/23/2007 287 of 691 •Increasing travel speed •Reduced penetration and width, undercut •Increasing arc voltage •Reduced penetration, increased width •Excessive voltage can cause porosity, spatter and undercut
Gas Metal Arc Welding 4/23/2007 289 of 691 Types of Shielding Gas MIG (Metal Inert Gas) • Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni) • Most common inert gas is Argon • Argon + Helium used to give a „hotter‟ arc - better for thicker joints and alloys with higher thermal conductivity
MIG/MAG – shielding gases 4/23/2007 290 of 691 Type of material Shielding gas Carbon steel Stainless steel Aluminium CO2 , Ar+(5-20)%CO2 Ar+2%O2 Ar
MIG/MAG shielding gases Argon (Ar): higher density than air; low thermal conductivity the arc has a high energy inner cone; good wetting at the toes; low ionisation potential Helium (He): lower density than air; high thermal conductivity uniformly distributed arc energy; parabolic profile; high ionisation potential Carbon Dioxide (CO2): cheap; deep penetration profile; cannot support spray transfer; poor wetting; high spatter 4/23/2007 291 of 691 Ar Ar-He He CO2
MIG/MAG shielding gases Gases for dip transfer: • CO2: carbon steels only: deep penetration; fast welding speed; high spatter levels • Ar + up to 25% CO2: carbon and low alloy steels: minimum spatter; good wetting and bead contour • 90% He + 7.5% Ar + 2.5% CO2:stainless steels: minimises undercut; small HAZ • Ar: Al, Mg, Cu, Ni and their alloys on thin sections • Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thicker sections (over 3 mm) 4/23/2007 292 of 691
MIG/MAG shielding gases Gases for spray transfer • Ar + (5-18)% CO2: carbon steels: minimum spatter; good wetting and bead contour • Ar + 2% O2: low alloy steels: minimise undercut; provides good toughness • Ar + 2% O2 or CO2: stainless steels: improved arc stability; provides good fusion • Ar: Al, Mg, Cu, Ni, Ti and their alloys • Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than pure Ar to offset heat dissipation • Ar + (25-30)% N2: Cu alloys: greater heat input 4/23/2007 293 of 691
Gas Metal Arc Welding Types of Shielding Gas MAG (Metal Active Gas) • Active gases used are Oxygen and Carbon Dioxide • Argon with a small % of active gas is required for all steels (including stainless steels) to ensure a stable arc & good droplet wetting into the weld pool • Typical active gases are Ar + 20% CO2 for C-Mn & low alloy steels Ar + 2% O2 for stainless steels 100% CO2 can be used for C - steels 4/23/2007 294 of 691
MIG/MAG Gas Metal Arc Welding Electrode orientation 4/23/2007 295 of 691 Penetration Deep Moderate Shallow Excess weld metal Maximum Moderate Minimum Undercut Severe Moderate Minimum Electrode extension •Increased extension
MIG / MAG - self-regulating arc 4/23/2007 296 of 691 Stable condition Sudden change in gun position L 19 mm 25 mmL‟ Arc length L = 6,4 mm Arc voltage = 24V Welding current = 250A WFS = 6,4 m/min Melt off rate = 6,4 m/min Arc length L‟ = 12,7 mm Arc voltage = 29V Welding current = 220A WFS = 6,4 m/min Melt off rate = 5,6 m/min Current (A) Voltage(V)
MIG/MAG - self-regulating arc 4/23/2007 297 of 691 Sudden change in gun position 25 mmL‟ Arc length L‟ = 12,7 mm Arc voltage = 29V Welding current = 220A WFS = 6,4 m/min Melt off rate = 5,6 m/min Current (A) Voltage(V) Re-established stable condition 25 mm L Arc length L = 6,4 mm Arc voltage = 24V Welding current = 250A WFS = 6,4 m/min Melt off rate = 6,4 m/min
Terminating the arc • Burnback time 4/23/2007 298 of 691 – delayed current cut-off to prevent wire freeze in the weld end crater – depends on WFS (set as short as possible!) Contact tip Workpiec e Burnback time 0.05 sec 0.10 sec 0.15 sec 14 mm 8 mm 3 mm Current - 250A Voltage - 27V WFS - 7,8 m/min Wire diam. - 1,2 mm Shielding gas - Ar+18%CO2 Insulatin g slag Crater fill
MIG/MAG - metal transfer modes Set-up for dip transfer Set-up for spray transfer 4/23/2007 299 of 691 Electrode extension 19-25 mm Contact tip recessed (3-5 mm) Contact tip extension (0-3,2 mm) Electrode extension 6-13 mm
MIG/MAG - metal transfer modes Current/voltage conditions4/23/2007 301 of 691 Current Voltage Dip transfer Spray transfer Globular transfer Electrode diameter = 1,2 mm WFS = 3,2 m/min Current = 145 A Voltage = 18-20V Electrode diameter = 1,2 mm WFS = 8,3 m/min Current = 295 A Voltage = 28V
MIG/MAG-methods of metal transfer 4/23/2007 303 of 691 Dip transfer Transfer occur due to short circuits between wire and weld pool, high level of spatter, need inductance control to limit current raise Can use pure CO2 or Ar- CO2 mixtures as shielding gas Metal transfer occur when arc is extinguished Requires low welding current/arc voltage, a low heat input process. Resulting in low residual stress and distortion Used for thin materials and all position welds
MIG/MAG-methods of metal transfer 4/23/2007 306 of 691 Spray transfer Transfer occur due to pinch effect NO contact between wire and weld pool! Requires argon-rich shielding gas Metal transfer occur in small droplets, a large volume weld pool Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion Used for thick materials and flat/horizontal position welds
MIG/MAG-methods of metal transfer 4/23/2007 307 of 691 Pulsed transfer Controlled metal transfer, one droplet per pulse, No transfer between droplet and weld pool! Requires special power sources Metal transfer occur in small droplets (diameter equal to that of electrode) Requires moderate welding current/arc voltage, a reduced heat input . Resulting in smaller residual stress and distortion compared to spray transfer Pulse frequency controls the volume of weld pool, used for root runs and out of position welds
MIG/MAG - metal transfer modes Pulsed transfer 4/23/2007 308 of 691 Controlled metal transfer. one droplet per pulse. NO transfer during background current! Requires special power sources Metal transfer occur in small droplets (diameter equal to that of electrode) Requires moderate welding current/arc voltage, reduced heat input‟ smaller residual stress and distortions compared to spray transfer Pulse frequency controls the volume of weld pool, used for root runs and out of position welds
MIG/MAG-methods of metal transfer 4/23/2007 310 of 691 Globular transfer Transfer occur due to gravity or short circuits between drops and weld pool Requires CO2 shielding gas Metal transfer occur in large drops (diameter larger than that of electrode) hence severe spatter Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion Non desired mode of transfer!
4/23/2007 315 of 691 O.C.V. Arc Voltage Virtually no Change. Voltage Flat or Constant Voltage Characteristic Used With MIG/MAG, ESW & SAW < 1000 amps 100 200 300 33 32 31 Large Current Change Small Voltage Change. Amperage Flat or Constant Voltage Characteristic
MIG/MAG welding gun assembly 4/23/2007 316 of 691 Contact tip Gas diffuser Handle Gas nozzle Trigger WFS remote control potentiometer Union nut The Push-Pull gun
Gas Metal Arc Welding 4/23/2007 318 of 691 PROCESS CHARACTERISTICS • Requires a constant voltage power source, gas supply, wire feeder, welding torch/gun and „hose package‟ • Wire is fed continuously through the conduit and is burnt-off at a rate that maintains a constant arc length/arc voltage • Wire feed speed is directly related to burn-off rate • Wire burn-off rate is directly related to current • When the welder holds the welding gun the process is said to be a semi-automatic process • The process can be mechanised and also automated • In Europe the process is usually called MIG or MAG
4/23/2007 322 of 691 Most welding imperfections in MIG/MAG are caused by lack of welder skill, or incorrect settings of the equipment •Worn contact tips will cause poor power pick up, or transfer •Bad power connections will cause a loss of voltage in the arc •Silica inclusions (in Fe steels) due to poor inter-run cleaning •Lack of fusion (primarily with dip transfer) •Porosity (from loss of gas shield on site etc) •Solidification problems (cracking, centerline pipes, crater pipes) especially on deep narrow welds MIG/MAG typical defects
WELDING PROCESS 4/23/2007 323 of 691 Flux Core Arc Welding (Not In The Training Manual)
Flux cored arc welding 4/23/2007 324 of 691 FCAW methods With gas shielding - “Outershield” Without gas shielding - “Innershield” With metal powder - “Metal core”
“Outershield” - principle of operation 4/23/2007 325 of 691
“Innershield” - principle of operation 4/23/2007 326 of 691
ARC CHARACTERISTICS 4/23/2007 327 of 691 Volts Amps OCV Constant Voltage Characteristic Small change in voltage = large change in amperage The self adjusting arc. Large arc gap Small arc gap
4/23/2007 328 of 691 Insulated extension nozzle Current carrying guild tube Flux cored hollow wire Flux powder Arc shield composed of vaporized and slag forming compounds Metal droplets covered with thin slag coating Molten weld poolSolidified weld metal and slag Flux core Wire joint Flux core wires Flux Core Arc Welding (FCAW)
Flux cored arc welding 4/23/2007 329 of 691 FCAW methods With gas shielding - “Outershield” Without gas shielding - “Innershield” (114) With metal powder - “Metal core” With active gas shielding (136) With inert gas shielding (137)
FCAW - differences from MIG/MAG • usually operates in DCEP but some “Innershield” wires operates in DCEN • power sources need to be more powerful due to the higher currents • doesn't work in deep transfer mode • require knurled feed rolls 4/23/2007 330 of 691 “Innershield” wires use a different type of welding gun
Backhand (“drag”) technique Advantages 4/23/2007 331 of 691 preferred method for flat or horizontal position slower progression of the weld deeper penetration weld stays hot longer, easy to remove dissolved gasses Disadvantages produce a higher weld profile difficult to follow the weld joint can lead to burn-through on thin sheet plates
Forehand (“push”) technique Advantages 4/23/2007 332 of 691 preferred method for vertical up or overhead position arc is directed towards the unwelded joint , preheat effect easy to follow the weld joint and control the penetration Disadvantages produce a low weld profile, with coarser ripples fast weld progression, shallower depth of penetration the amount of spatter can increase
FCAW advantages • less sensitive to lack of fusion • requires smaller included angle compared to MMA • high productivity • all positional • smooth bead surface, less danger of undercut • basic types produce excellent toughness properties • good control of the weld pool in positional welding especially with rutile wires • seamless wires have no torsional strain, twist free • ease of varying the alloying constituents • no need for shielding gas 4/23/2007 333 of 691
FCAW disadvantages • limited to steels and Ni-base alloys • slag covering must be removed • FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels) • for gas shielded process, the gaseous shield may be affected by winds and drafts • more smoke and fumes are generated compared with MIG/MAG • in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire) 4/23/2007 334 of 691
4/23/2007 335 of 691 Advantages: 1) Field or shop use 2) High productivity 3) All positional 4) Slag supports and shapes the weld Bead 5) No need for shielding gas Disadvantages: 1) High skill factor 2) Slag inclusions 3) Cored wire is Expensive 4) High level of fume (Inner-shield) 5) Limited to steels and nickel alloys FCAW advantages/disadvantages
Welding Inspector Submerged Arc Welding Section 13 4/23/2007 336 of 691
4/23/2007 337 of 691 • Submerged arc welding was developed in the Soviet Union during the 2nd world war for the welding of thick section steel. • The process is normally mechanized. • The process uses amps in the range of 100 to over 2000, which gives a very high current density in the wire producing deep penetration and high dilution welds. • A flux is supplied separately via a flux hopper in the form of either fused or agglomerated. • The arc is not visible as it is submerged beneath the flux layer and no eye protection is required. Submerged Arc Welding Introduction
SAW Principle of operation 4/23/2007 338 of 691
Principles of operation 4/23/2007 339 of 691 Factors that determine whether to use SAW chemical composition and mechanical properties required for the weld deposit • thickness of base metal to be welded • joint accessibility • position in which the weld is to be made • frequency or volume of welding to be performed SAW methods Semiautomatic Mechanised Automatic
Submerged Arc Welding 4/23/2007 340 of 691 - + Power supply Filler wire spool Flux hopper Wire electrode Flux Slide rail
SAW process variables 4/23/2007 341 of 691 • welding current • current type and polarity • welding voltage • travel speed • electrode size • electrode extension • width and depth of the layer of flux
SAW process variables 4/23/2007 342 of 691 Welding current •controls depth of penetration and the amount of base metal melted & dilution
SAW operating variables 4/23/2007 343 of 691 Current type and polarity •Usually DCEP, deep penetration, better resistance to porosity •DCEN increase deposition rate but reduce penetration (surfacing) •AC used to avoid arc blow; can give unstable arc
SAW Consumables (Covered in detail in Section 14) 4/23/2007 344 of 691 Fused fluxes advantages: •good chemical homogeneity •easy removal of fines without affecting flux composition •normally not hygroscopic & easy storage and handling •readily recycled without significant change in particle size or composition Fused fluxes disadvantages: •difficult to add deoxidizers and ferro-alloys (due to segregation or extremely high loss) •high temperatures needed to melt ingredients limit the range of flux compositions
SAW Consumables 4/23/2007 345 of 691 Agglomerated fluxes advantages: • easy addition of deoxidizers and alloying elements • usable with thicker layer of flux when welding • colour identification Agglomerated fluxes disadvantages: • tendency to absorb moisture • possible gas evolution from the molten slag leading to porosity • possible change in flux composition due to segregation or removal of fine mesh particles
SAW equipment 4/23/2007 346 of 691 Power sources can be: • transformers for AC • transformer-rectifiers for DC Static characteristic can be: • Constant Voltage (flat) - most of the power sources • Constant Current (drooping)
SAW equipment 4/23/2007 347 of 691 Constant Voltage (Flat Characteristic) power sources: • most commonly used supplies for SAW • can be used for both semiautomatic and automatic welding • self-regulating arc • simple wire feed speed control • wire feed speed controls the current and power supply controls the voltage • applications for DC are limited to 1000A due to severe arc blow (also thin wires!)
ARC CHARACTERISTICS 4/23/2007 348 of 691 Volts Amps OCV Constant Voltage Characteristic Small change in voltage = large change in amperage The self adjusting arc. Large arc gap Small arc gap
SAW equipment 4/23/2007 349 of 691 Constant Current (Drooping Characteristic) power sources: • Over 1000A - very fast speed required - control of burn off rate and stick out length • can be used for both semiautomatic and automatic welding • not self-regulating arc • must be used with a voltage-sensing variable wire feed speed control • more expensive due to more complex wire feed speed control • arc voltage depends upon wire feed speed whilst the power source controls the current • cannot be used for high-speed welding of thin steel
SAW equipment 4/23/2007 350 of 691 Welding heads can be mounted on a: Tractor type carriage • provides travel along straight or gently curved joints • can ride on tracks set up along the joint (with grooved wheels) or on the workpiece itself • can use guide wheels as tracking device • due to their portability, are used in field welding or where the piece cannot be moved Courtesy of ESAB AB Courtesy of ESAB AB
SAW operating variables 4/23/2007 351 of 691 Welding current •too high current: excessive excess weld metal (waste of electrode), increase weld shrinkage and causes greater distortions •excessively high current: digging arc, undercut, burn through; also a high and narrow bead & solidification cracking •too low current: incomplete fusion or inadequate penetration •excessively low current: unstable arc
SAW operating variables 4/23/2007 352 of 691 Welding voltage •welding voltage controls arc length •an increased voltage can increase pick-up of alloying elements from an alloy flux •increase in voltage produce a flatter and wider bead •increase in voltage increase flux consumption •increase in voltage tend to reduce porosity •an increased voltage may help bridging an excessive root gap
SAW operating variables 4/23/2007 353 of 691 Welding voltage •low voltage produce a “stiffer” arc & improves penetration in a deep weld groove and resists arc blow •excessive low voltage produce a high narrow bead & difficult slag removal
SAW operating variables 4/23/2007 354 of 691 Welding voltage •excessively high voltage produce a “hat-shaped” bead & tendency to crack •excessively high voltage increase undercut & make slag removal difficult in groove welds •excessively high voltage produce a concave fillet weld that is subject to cracking
SAW operating variables 4/23/2007 355 of 691 Travel speed •increase in travel speed: decrease heat input & less filler metal applied per unit of length, less excess weld metal & weld bead becomes smaller
SAW operating variables 4/23/2007 356 of 691 Travel speed •excessively high speed lead to undercut, arc blow and porosity •excessively low speed produce “hat-shaped” beads danger of cracking •excessively low speed produce rough beads and lead to slag inclusions
SAW operating variables 4/23/2007 357 of 691 Electrode size •at the same current, small electrodes have higher current density & higher deposition rates
SAW operating variables 4/23/2007 358 of 691 Electrode extension •increased electrode extension adds resistance in the welding circuit I increase in deposition rate, decrease in penetration and bead width •to keep a proper weld shape, when electrode extension is increased, voltage must also be increased •when burn-through is a problem (e.g. thin gauge), increase electrode extension •excessive electrode extension: it is more difficult to maintain the electrode tip in the correct position
SAW operating variables 4/23/2007 359 of 691 Depth of flux •depth of flux layer influence the appearance of weld •usually, depth of flux is 25-30 mm •if flux layer is to deep the arc is too confined, result is a rough ropelike appearing weld •if flux layer is to deep the gases cannot escape & the surface of molten weld metal becomes irregularly distorted •if flux layer is too shallow, flashing and spattering will occur, give a poor appearance and porous weld
SAW technological variables 4/23/2007 363 of 691 Travel angle effect - Butt weld on plates Penetration Deep Moderate Shallow Excess weld metal Maximum Moderate Minimum Tendency to undercut Severe Moderate Minimum
SAW technological variables 4/23/2007 364 of 691 Earth position + - Direction of travel •welding towards earth produces backward arc blow •deep penetration •convex weld profile
SAW technological variables 4/23/2007 365 of 691 Earth position + - Direction of travel •welding away earth produces forward arc blow •normal penetration depth •smooth, even weld profile
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61769477 welding-inspection-cswip-gud

  • 1. Welding Inspector 4/23/2007 1 of 691 Duties and Responsibilities Section 1
  • 2. Main Responsibilities 1.1 4/23/2007 2 of 691 • Code compliance • Workmanship control • Documentation control
  • 3. Personal Attributes 1.1 Important qualities that good Inspectors are expected to have are: •Honesty •Integrity •Knowledge •Good communicator •Physical fitness •Good eyesight 4/23/2007 3 of 691
  • 4. Standard for Visual Inspection 1.1 Basic Requirements 4/23/2007 4 of 691 BS EN 970 - Non-destructive examination of fusion welds - Visual examination Welding Inspection Personnel should: • be familiar with relevant standards, rules and specifications applicable to the fabrication work to be undertaken • be informed about the welding procedures to be used • have good vision (which should be checked every 12 months)
  • 5. Welding Inspection 1.2 4/23/2007 5 of 691 Conditions for Visual Inspection (to BS EN 970) Illumination: • 350 lux minimum required • (recommends 500 lux - normal shop or office lighting) Vision Access: • eye should be within 600mm of the surface • viewing angle (line from eye to surface) to be not less than 30° 30° 600mm
  • 6. Welding Inspection 1.3 Aids to Visual Inspection (to BS EN 970) When access is restricted may use: • a mirrored boroscope • a fibre optic viewing system Other aids: • welding gauges (for checking bevel angles, weld profile, fillet sizing, undercut depth) • dedicated weld-gap gauges and linear misalignment (high-low) gauges • straight edges and measuring tapes • magnifying lens (if magnification lens used it should have magnification between X2 to X5) 4/23/2007 6 of 691 usually by agreement }
  • 7. Welding Inspectors Equipment 1.3 Measuring devices: • flexible tape, steel rule • Temperature indicating crayons • Welding gauges • Voltmeter • Ammeter • Magnifying glass • Torch / flash light • Gas flow-meter 4/23/2007 7 of 691
  • 8. Welding Inspectors Gauges 1.3 4/23/2007 8 of 691 TWI Multi-purpose Welding Gauge Misalignment Gauges Hi-Lo Gauge Fillet Weld Gauges G.A.L. S.T.D. 10mm 16mm L G.A.L. S.T.D. 10mm 16mm 0 1/4 1/2 3/4 IN HI-LOSinglePurposeWeldingGauge 1 2 3 4 5 6
  • 9. Welding Inspectors Equipment 1.3 4/23/2007 9 of 691 Tong Tester AmmeterVoltmeter
  • 10. Welding Inspection 1.3 4/23/2007 10 of 691 Stages of Visual Inspection (to BS EN 970) Extent of examination and when required should be defined in the application standard or by agreement between the contracting parties For high integrity fabrications inspection required throughout the fabrication process: Before welding (Before assemble & After assembly) During welding After welding
  • 11. Typical Duties of a Welding Inspector 1.5 4/23/2007 11 of 691 Before Welding Preparation: Familiarisation with relevant „documents‟… • Application Standard/Code - for visual acceptance requirements • Drawings - item details and positions/tolerances etc • Quality Control Procedures - for activities such as material handling, documentation control, storage & issue of welding consumables • Quality Plan/Inspection & Test Plan/Inspection Checklist - details of inspection requirements, inspection procedures & records required
  • 12. Typical Duties of a Welding Inspector 1.5 4/23/2007 12 of 691 Before Welding Welding Procedures: • are applicable to joints to be welded & approved • are available to welders & inspectors Welder Qualifications: • list of available qualified welders related to WPS‟s • certificates are valid and ‘in-date’
  • 13. Typical Duties of a Welding Inspector 1.5 Before Welding Equipment: • all inspection equipment is in good condition & calibrated as necessary • all safety requirements are understood & necessary equipment available Materials: • can be identified & related to test certificates, traceability ! • are of correct dimensions • are in suitable condition (no damage/contamination) 4/23/2007 13 of 691
  • 14. Typical Duties of a Welding Inspector 1.5 Before Welding Consumables: • in accordance with WPS’s • are being controlled in accordance with Procedure Weld Preparations: • comply with WPS/drawing • free from defects & contamination Welding Equipment: • in good order & calibrated as required by Procedure 4/23/2007 14 of 691
  • 15. Typical Duties of a Welding Inspector 1.5 Before Welding Fit-up • complies with WPS • Number / size of tack welds to Code / good workmanship Pre-heat • if specified • minimum temperature complies with WPS 4/23/2007 15 of 691
  • 16. Typical Duties of a Welding Inspector 1.5 4/23/2007 16 of 691 During Welding Weather conditions • suitable if site / field welding Welding Process(es) • in accordance with WPS Welder • is approved to weld the joint Pre-heat (if required) • minimum temperature as specified by WPS • maximum interpass temperature as WPS
  • 17. Typical Duties of a Welding Inspector 1.6 During Welding Welding consumables • in accordance with WPS • in suitable condition • controlled issue and handling Welding Parameters • current, voltage & travel speed – as WPS Root runs • if possible, visually inspect root before single-sided welds are filled up 4/23/2007 17 of 691
  • 18. Typical Duties of a Welding Inspector 1.6 During Welding Inter-run cleaning in accordance with an approved method (& back gouging) to good workmanship standard Distortion control • welding is balanced & over-welding is avoided 4/23/2007 18 of 691
  • 19. Typical Duties of a Welding Inspector 1.6 4/23/2007 19 of 691 After Welding Weld Identification • identified/numbered as required • is marked with welder‟s identity Visual Inspection • ensure weld is suitable for all NDT • visually inspect & „sentence‟ to Code requirements Dimensional Survey • ensure dimensions comply with Code/drawing Other NDT • ensure all NDT is completed & reports available
  • 20. Typical Duties of a Welding Inspector 1.6 After Welding Repairs • monitor repairs to ensure compliance with Procedure, ensure NDT after repairs is completed • PWHT • monitor for compliance with Procedure • check chart records confirm Procedure compliance Pressure / Load Test • ensure test equipment is suitably calibrated • monitor to ensure compliance with Procedure • ensure all records are available 4/23/2007 20 of 691
  • 21. Typical Duties of a Welding Inspector 1.6 After Welding Documentation • ensure any modifications are on ‘as-built’ drawings • ensure all required documents are available • Collate / file documents for manufacturing records • Sign all documentation and forward it to QC department. 4/23/2007 21 of 691
  • 22. Summary of Duties A Welding Inspector must: • Observe To observe all relevant actions related to weld quality throughout production. • Record To record, or log all production inspection points relevant to quality, including a final report showing all identified imperfections • Compare To compare all recorded information with the acceptance criteria and any other relevant clauses in the applied application standard 4/23/2007 22 of 691 It is the duty of a Welding Inspector to ensure all the welding and associated actions are carried out in accordance with the specification and any applicable procedures.
  • 23. Welding Inspector Terms & Definitions Section 2 4/23/2007 23 of 691
  • 24. Welding Terminology & Definitions 2.1 4/23/2007 24 of 691 What is a Weld? • A localised coalescence of metals or non-metals produced either by heating the materials to the welding temperature, with or without the application of pressure, or by the application of pressure alone (AWS) • A permanent union between materials caused by heat, and or pressure (BS499) • An Autogenous weld: A weld made with out the use of a filler material and can only be made by TIG or Oxy-Gas Welding
  • 25. Welding Terminology & Definitions 2.1 What is a Joint? • The junction of members or the edges of members that are to be joined or have been joined (AWS) • A configuration of members (BS499) 4/23/2007 25 of 691
  • 26. Joint Terminology 2.2 4/23/2007 26 of 691 Edge Open & Closed Corner Lap Tee Butt Cruciform
  • 27. Welded Butt Joints 2.2 4/23/2007 27 of 691 A_________Welded butt jointButt A_________Welded butt jointFillet A____________Welded butt jointCompound
  • 28. 4/23/2007 28 of 691 Welded Tee Joints 2.2 A_________Welded T jointFillet A_________Welded T jointButt A____________Welded T jointCompound
  • 29. Weld Terminology 2.3 4/23/2007 29 of 691 Compound weld Fillet weld Butt weld Edge weld Spot weld Plug weld
  • 30. Butt Preparations – Sizes 2.4 4/23/2007 30 of 691 Full Penetration Butt Weld Partial Penetration Butt Weld Design Throat Thickness Design Throat Thickness Actual Throat Thickness Actual Throat Thickness
  • 31. 4/23/2007 31 of 691 Weld Zone Terminology 2.5 Weld Boundary C A B D Heat Affected Zone Root Weld metal A, B, C & D = Weld Toes Face
  • 32. Weld Zone Terminology 2.5 4/23/2007 32 of 691 Excess Root Penetration Excess Cap height or Weld Reinforcement Weld cap width Design Throat Thickness Actual Throat Thickness
  • 33. Heat Affected Zone (HAZ) 2.5 4/23/2007 33 of 691 tempered zone grain growth zone recrystallised zone partially transformed zone Maximum Temperature solid-liquid Boundarysolid weld metal unaffected base material
  • 34. Joint Preparation Terminology 2.7 4/23/2007 34 of 691 Included angle Root Gap Root Face Angle of bevel Root Face Root Gap Included angle Root Radius Single-V Butt Single-U Butt
  • 35. Joint Preparation Terminology 2.8 & 2.9 4/23/2007 35 of 691 Root Gap Root Face Root FaceRoot Gap Root Radius Single Bevel Butt Single-J Butt Angle of bevel Angle of bevel Land
  • 36. Single Sided Butt Preparations 2.10 4/23/2007 36 of 691 Single Bevel Single Vee Single-J Single-U Single sided preparations are normally made on thinner materials, or when access form both sides is restricted
  • 37. Double Sided Butt Preparations2.11 4/23/2007 37 of 691 Double sided preparations are normally made on thicker materials, or when access form both sides is unrestricted -VeeDouble-BevelDouble - JDouble - UDouble
  • 38. Weld Preparation 4/23/2007 38 of 691 Terminology & Typical Dimensions: V-Joints bevel angle root face root gap included angle Typical Dimensions bevel angle 30 to 35° root face ~1.5 to ~2.5mm root gap ~2 to ~4mm
  • 39. Butt Weld - Toe Blend 4/23/2007 39 of 691 6 mm 80 Poor Weld Toe Blend Angle Improved Weld Toe Blend Angle 20 3 mm •Most codes quote the weld toes shall blend smoothly •This statement is not quantitative and therefore open to individual interpretation •The higher the toe blend angle the greater the amount of stress concentration •The toe blend angle ideally should be between 20o-30o
  • 40. Fillet Weld Features 2.13 4/23/2007 40 of 691 Design Throat Vertical Leg Length Horizontal leg Length Excess Weld Metal
  • 41. Fillet Weld Throat Thickness 2.13 4/23/2007 41 of 691 b a b = Actual Throat Thickness a = Design Throat Thickness
  • 42. Deep Penetration Fillet Weld Features2.13 4/23/2007 42 of 691 b a b = Actual Throat Thickness a = Design Throat Thickness
  • 43. Fillet Weld Sizes 2.14 Calculating Throat Thickness from a known Leg Length: Design Throat Thickness = Leg Length x 0.7 Question: The Leg length is 14mm. What is the Design Throat? Answer: 14mm x 0.7 = 10mm Throat Thickness 4/23/2007 43 of 691
  • 44. Fillet Weld Sizes 2.14 Calculating Leg Length from a known Design Throat Thickness: Leg Length = Design Throat Thickness x 1.4 Question: The Design Throat is 10mm. What is the Leg length? Answer: 10mm x 1.4 = 14mm Leg Length 4/23/2007 44 of 691
  • 45. Features to Consider 2 2.14 Importance of Fillet Weld Leg Length Size 4/23/2007 45 of 691 Approximately the same weld volume in both Fillet Welds, but the effective throat thickness has been altered, reducing considerably the strength of weld B 2mm (b) 4mm 8mm (a) 4mm
  • 46. Fillet Weld Sizes 2.14 Importance of Fillet weld leg length Size 4/23/2007 46 of 691 Area = 4 x 4 = 8mm2 2 Area = 6 x 6 = 18mm2 2 The c.s.a. of (b) is over double the area of (a) without the extra excess weld metal being added 4mm 6mm (a) (b) 4mm 6mm (a) (b) Excess Excess
  • 47. 4/23/2007 47 of 691 Fillet Weld Profiles 2.15 Mitre Fillet Convex Fillet Concave Fillet A concave profile is preferred for joints subjected to fatigue loading Fillet welds - Shape
  • 48. EFFECTIVE THROAT THICKNESS 4/23/2007 48 of 691 “s” = Effective throat thickness sa “a” = Nominal throat thickness Deep penetration fillet welds from high heat input welding process MAG, FCAW & SAW etc Fillet Features to Consider 2.15
  • 49. Welding Positions 2.17 PA 1G / 1F Flat / Downhand PB 2F Horizontal-Vertical PC 2G Horizontal PD 4F Horizontal-Vertical (Overhead) PE 4G Overhead PF 3G / 5G Vertical-Up PG 3G / 5G Vertical-Down H-L045 6G Inclined Pipe (Upwards) J-L045 6G Inclined Pipe (Downwards) 4/23/2007 49 of 691
  • 51. Welding position designation2.17 Butt welds in plate (see ISO 6947) 4/23/2007 51 of 691 Flat - PA Overhead - PE Vertical up - PF Vertical down - PG Horizontal - PC
  • 52. Welding position designation 2.17 Butt welds in pipe (see ISO 6947) 4/23/2007 52 of 691 Flat - PA axis: horizontal pipe: rotated H-L045 axis: inclined at 45° pipe: fixed Horizontal - PC axis: vertical pipe: fixed Vertical up - PF axis: horizontal pipe: fixed Vertical down - PG axis: horizontal pipe: fixed J-L045 axis: inclined at 45° pipe: fixed
  • 53. Welding position designation2.17 Fillet welds on plate (see ISO 6947) 4/23/2007 53 of 691 Flat - PA Overhead - PD Vertical up - PF Vertical down - PG Horizontal - PB
  • 54. Welding position designation 2.17 Fillet welds on pipe (see ISO 6947) 4/23/2007 54 of 691 Flat - PA axis: inclined at 45° pipe: rotated Overhead - PD axis: vertical pipe: fixed Vertical up - PF axis: horizontal pipe: fixed Vertical down - PG axis: horizontal pipe: fixed Horizontal - PB axis: vertical pipe: fixed Horizontal - PB axis: horizontal pipe: rotated
  • 55. 4/23/2007 55 of 691 Plate/Fillet Weld Positions2.17 PA / 1G PA / 1F PC / 2G PB / 2F PD / 4F PE / 4G PG / 3G PF / 3G
  • 56. 4/23/2007 56 of 691 Pipe Welding Positions 2.17 Weld: Flat Pipe: rotated Axis: Horizontal PA / 1G Weld: Vertical Downwards Pipe: Fixed Axis: Horizontal PG / 5G Weld: Vertical upwards Pipe: Fixed Axis: Horizontal PF / 5G Weld: Upwards Pipe: Fixed Axis: Inclined Weld: Horizontal Pipe: Fixed Axis: Vertical PC / 2G 45o Weld: Downwards Pipe: Fixed Axis: Inclined J-LO 45 / 6G 45o H-LO 45 / 6G
  • 57. Travel Speed Measurement2.18 4/23/2007 57 of 691 Definition: the rate of weld progression measured in case of mechanised and automatic welding processes in case of MMA can be determined using ROL and arc time
  • 59. Welding Imperfections 3.1 4/23/2007 59 of 691 All welds have imperfections • Imperfections are classed as defects when they are of a type, or size, not allowed by the Acceptance Standard A defect is an unacceptable imperfection • A weld imperfection may be allowed by one Acceptance Standard but be classed as a defect by another Standard and require removal/rectification
  • 60. Welding Imperfections 3.1 4/23/2007 60 of 691 Standards for Welding Imperfections BS EN ISO 6520-1(1998) Welding and allied processes – Classification of geometric imperfections in metallic materials - Part 1: Fusion welding Imperfections are classified into 6 groups, namely: 1 Cracks 2 Cavities 3 Solid inclusions 4 Lack of fusion and penetration 5 Imperfect shape and dimensions 6 Miscellaneous imperfections
  • 61. Welding Imperfections 3.1 4/23/2007 61 of 691 Standards for Welding Imperfections EN ISO 5817 (2003) Welding - Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding excluded) - Quality levels for imperfections This main imperfections given in EN ISO 6520-1 are listed in EN ISO 5817 with acceptance criteria at 3 levels, namely Level B (highest) Level C (intermediate) Level D (general) This Standard is „directly applicable to visual testing of welds‟ ...(weld surfaces & macro examination)
  • 63. Cracks 3.1 Cracks that may occur in welded materials are caused generally by many factors and may be classified by shape and position. Note: Cracks are classed as Planar Defects. 4/23/2007 63 of 691 Classified by Shape •Longitudinal •Transverse •Chevron •Lamellar Tear Classified by Position •HAZ •Centerline •Crater •Fusion zone •Parent metal
  • 64. Cracks 3.1 4/23/2007 64 of 691 Longitudinal parent metal Longitudinal weld metal Lamellar tearing Transverse weld metal
  • 65. Cracks 3.1 4/23/2007 65 of 691 Transverse crack Longitudinal crack
  • 66. Cracks 3.2 Main Crack Types • Solidification Cracks • Hydrogen Induced Cracks • Lamellar Tearing • Reheat cracks 4/23/2007 66 of 691
  • 67. Cracks 3.2 Solidification Cracking • Occurs during weld solidification process • Steels with high sulphur impurities content (low ductility at elevated temperature) • Requires high tensile stress • Occur longitudinally down centre of weld 4/23/2007 67 of 691
  • 68. Cracks 3.3 Hydrogen Induced Cold Cracking • Requires susceptible hard grain structure, stress, low temperature and hydrogen • Hydrogen enters weld via welding arc mainly as result of contaminated electrode or preparation • Hydrogen diffuses out into parent metal on cooling • Cracking developing most likely in HAZ 4/23/2007 68 of 691
  • 69. Lamellar Tearing3.5 • Location: Parent metal • Steel Type: Any steel type possible • Susceptible Microstructure: Poor through thickness ductility • Lamellar tearing has a step like appearance due to the solid inclusions in the parent material (e.g. sulphides and silicates) linking up under the influence of welding stresses • Low ductile materials in the short transverse direction containing high levels of impurities are very susceptible to lamellar tearing • It forms when the welding stresses act in the short transverse direction of the material (through thickness direction) 4/23/2007 69 of 691
  • 70. Gas Cavities 3.6 4/23/2007 70 of 691 Root piping Cluster porosityGas pore Blow hole Herringbone porosity Gas pore <1.5mm Blow hole.>1.6mm Causes: •Loss of gas shield •Damp electrodes •Contamination •Arc length too large •Damaged electrode flux •Moisture on parent material •Welding current too low
  • 71. Gas Cavities 3.7 4/23/2007 71 of 691 Root piping Porosity
  • 72. Gas Cavities 3.8 4/23/2007 72 of 691 Cluster porosity Herringbone porosity
  • 73. 4/23/2007 73 of 691 Crater pipe Weld crater Crater Pipe 3.9
  • 74. 4/23/2007 74 of 691 Crater pipe is a shrinkage defect and not a gas defect, it has the appearance of a gas pore in the weld crater Causes: • Too fast a cooling rate • Deoxidization reactions and liquid to solid volume change • Contamination Crater cracks (Star cracks) Crater pipe Crater Pipe 3.9
  • 75. Solid Inclusions3.10 Slag inclusions are defined as a non-metallic inclusion caused by some welding process 4/23/2007 75 of 691 Causes: •Slag originates from welding flux •MAG and TIG welding process produce silica inclusions •Slag is caused by inadequate cleaning •Other inclusions include tungsten and copper inclusions from the TIG and MAG welding process Slag inclusions Parallel slag lines Lack of sidewall fusion with associated slag Lack of interun fusion + slag
  • 76. Solid Inclusions 3.11 4/23/2007 76 of 691 Elongated slag linesInterpass slag inclusions
  • 77. Welding Imperfections 3.13 4/23/2007 77 of 691 Typical Causes of Lack of Fusion: • welding current too low • bevel angle too steep • root face too large (single-sided weld) • root gap too small (single-sided weld) • incorrect electrode angle • linear misalignment • welding speed too high • welding process related – particularly dip-transfer GMAW • flooding the joint with too much weld metal (blocking Out)
  • 78. Lack of Fusion3.13 4/23/2007 78 of 691 Incomplete filled groove + Lack of sidewall fusion 1 2 1. Lack of sidewall fusion 2. Lack of inter-run fusion Causes: •Poor welder skill • Incorrect electrode manipulation • Arc blow • Incorrect welding current/voltage • Incorrect travel speed • Incorrect inter-run cleaning
  • 79. 4/23/2007 79 of 691 Lack of sidewall fusion + incomplete filled groove Lack of Fusion 3.13
  • 80. 4/23/2007 80 of 691 Weld Root Imperfections 3.15 Lack of Root Fusion Lack of Root Penetration
  • 81. 4/23/2007 81 of 691 Cap Undercut3.18 Intermittent Cap Undercut
  • 82. Undercut 3.18 4/23/2007 82 of 691 Cap undercutRoot undercut
  • 83. Surface and Profile 3.19 4/23/2007 83 of 691 Incomplete filled groove Poor cap profile Excessive cap height Poor cap profiles and excessive cap reinforcements may lead to stress concentration points at the weld toes and will also contribute to overall poor toe blend
  • 84. Surface and Profile 3.19 4/23/2007 84 of 691 Incomplete filled grooveExcess cap reinforcement
  • 85. 4/23/2007 85 of 691 Excessive root penetration Weld Root Imperfections3.20
  • 86. Overlap 3.21 4/23/2007 86 of 691 An imperfection at the toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it Causes: •Contamination •Slow travel speed •Incorrect welding technique •Current too low
  • 87. Overlap 3.21 4/23/2007 87 of 691 Toe Overlap Toe Overlap
  • 88. Set-Up Irregularities 3.22 4/23/2007 88 of 691 Plate/pipe Linear Misalignment (Hi-Lo) Angular Misalignment Linear misalignment is measured from the lowest plate to the highest point. Angular misalignment is measured in degrees
  • 89. Set-Up Irregularities3.22 4/23/2007 89 of 691 Linear Misalignment
  • 90. Set-Up Irregularities3.22 4/23/2007 90 of 691 Linear Misalignment
  • 91. 4/23/2007 91 of 691 Lack of sidewall fusion + incomplete filled groove Incomplete Groove3.23
  • 92. 4/23/2007 92 of 691 Concave Root Causes: • Excessive back purge pressure during TIG welding Excessive root bead grinding before the application of the second pass welding current too high for 2nd pass overhead welding root gap too large - excessive „weaving‟ A shallow groove, which may occur in the root of a butt weld Weld Root Imperfections3.24
  • 93. 4/23/2007 93 of 691 Concave Root Weld Root Imperfections 3.24
  • 94. Weld Root Imperfections 3.24 4/23/2007 94 of 691 Concave root Excess root penetration
  • 95. 4/23/2007 95 of 691 Causes: • High Amps/volts • Small Root face • Large Root Gap • Slow Travel SpeedBurn through A localized collapse of the weld pool due to excessive penetration resulting in a hole in the root run Weld Root Imperfections 3.25
  • 96. Weld Root Imperfections3.25 4/23/2007 96 of 691 Burn Through
  • 97. 4/23/2007 97 of 691 Causes: • Loss or insufficient back purging gas (TIG) • Most commonly occurs when welding stainless steels • Purging gases include argon, helium and occasionally nitrogen Oxidized Root (Root Coking)
  • 98. 4/23/2007 98 of 691 Miscellaneous Imperfections 3.26 Arc strike Causes: • Accidental striking of the arc onto the parent material • Faulty electrode holder • Poor cable insulation • Poor return lead clamping
  • 99. Miscellaneous Imperfections3.27 4/23/2007 99 of 691 Causes: • Excessive current • Damp electrodes • Contamination • Incorrect wire feed speed when welding with the MAG welding process • Arc blowSpatter
  • 100. Mechanical Damage3.28 Mechanical damage can be defined as any surface material damage cause during the manufacturing process. 4/23/2007 100 of 691 • Grinding • Hammering • Chiselling • Chipping • Breaking off welded attachments (torn surfaces) • Using needle guns to compress weld capping runs
  • 101. Mechanical Damage 3.28 4/23/2007 101 of 691 Mechanical Damage/Grinding Mark Chipping Marks
  • 103. Qualitative and Quantitative Tests4.1 The following mechanical tests have units and are termed quantitative tests to measure Mechanical Properties • Tensile tests (Transverse Welded Joint, All Weld Metal) • Toughness testing (Charpy, Izod, CTOD) • Hardness tests (Brinell, Rockwell, Vickers) The following mechanical tests have no units and are termed qualitative tests for assessing joint quality • Macro testing • Bend testing • Fillet weld fracture testing • Butt weld nick-break testing 4/23/2007 104 of 691
  • 104. Mechanical Test Samples 4.1 4/23/2007 105 of 691 Tensile Specimens Fracture Fillet Specimen CTOD Specimen Charpy Specimen Bend Test Specimen
  • 105. Destructive Testing4.1 4/23/2007 106 of 691 Typical Positions for Test Pieces Specimen Type Position •Macro + Hardness 5 •Transverse Tensile 2, 4 •Bend Tests 2, 4 •Charpy Impact Tests 3 •Additional Tests 3 WELDING PROCEDURE QUALIFICATION TESTING 2 3 4 5 top of fixed pipe
  • 106. Definitions 4/23/2007 107 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Ability of a material to withstand deformation under static compressive loading without rupture Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
  • 107. Definitions 4/23/2007 108 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Ability of a material undergo plastic deformation under static tensile loading without rupture. Measurable elongation and reduction in cross section area Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
  • 108. Definitions 4/23/2007 109 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Ability of a material to withstand bending or the application of shear stresses by impact loading without fracture. Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
  • 109. Definitions 4/23/2007 110 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Measurement of a materials surface resistance to indentation from another material by static load Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
  • 110. Definitions 4/23/2007 111 of 691 • Malleability • Ductility • Toughness • Hardness • Tensile Strength Measurement of the maximum force required to fracture a materials bar of unit cross-sectional area in tension Mechanical Properties of metals are related to the amount of deformation which metals can withstand under different circumstances of force application.
  • 111. Transverse Joint Tensile Test4.2 Weld on plate 4/23/2007 112 of 691 Multiple cross joint specimensWeld on pipe
  • 112. Tensile Test 4.3 4/23/2007 113 of 691 All-Weld Metal Tensile Specimen Transverse Tensile Specimen
  • 113. STRA (Short Transverse Reduction Area) For materials that may be subject to Lamellar Tearing 4/23/2007 114 of 691
  • 114. UTS Tensile test 4.4 4/23/2007 115 of 691
  • 115. Charpy V-Notch Impact Test4.5 4/23/2007 116 of 691 Objectives: • measuring impact strength in different weld joint areas • assessing resistance toward brittle fracture Information to be supplied on the test report: • Material type • Notch type • Specimen size • Test temperature • Notch location • Impact Strength Value
  • 116. Ductile / Brittle Transition Curve4.6 4/23/2007 117 of 691 - 50 0- 20 - 10- 40 - 30 Ductile fracture Ductile/Brittle transition point 47 Joules 28 Joules Testing temperature - Degrees Centigrade Temperature range Transition range Brittle fracture Three specimens are normally tested at each temperature Energy absorbed
  • 117. Comparison Charpy Impact Test Results4.6 4/23/2007 118 of 691 Impact Energy Joules Room Temperature -20oC Temperature 1. 197 Joules 2. 191 Joules 3. 186 Joules 1. 49 Joules 2. 53 Joules 3. 51 Joules Average = 191 Joules Average = 51 Joules The test results show the specimens carried out at room temperature absorb more energy than the specimens carried out at -20oC
  • 118. Charpy V-notch impact test specimen4.7 4/23/2007 119 of 691 Specimen dimensions according ASTM E23 ASTM: American Society of Testing Materials
  • 119. Charpy V-Notch Impact Test 4.8 4/23/2007 120 of 691 Specime n Pendulu m (striker) Anvil (support)
  • 120. Charpy Impact Test4.9 4/23/2007 121 of 691 10 mm8mm2mm 22.5o Machined notch 100% Ductile Machined notch Large reduction in area, shear lips Fracture surface 100% bright crystalline brittle fracture Randomly torn, dull gray fracture surface 100% Brittle
  • 121. Hardness Testing4.10 4/23/2007 122 of 691 Definition Measurement of resistance of a material against penetration of an indenter under a constant load There is a direct correlation between UTS and hardness Hardness tests: Brinell Vickers Rockwell
  • 122. Hardness Testing 4.10 4/23/2007 123 of 691 Objectives: • measuring hardness in different areas of a welded joint • assessing resistance toward brittle fracture, cold cracking and corrosion sensitivity within a H2S (Hydrogen Sulphide) environment. Information to be supplied on the test report: • material type • location of indentation • type of hardness test and load applied on the indenter • hardness value
  • 123. Vickers Hardness Test 4.11 4/23/2007 124 of 691 Vickers hardness tests: indentation body is a square based diamond pyramid (136º included angle) the average diagonal (d) of the impression is converted to a hardness number from a table it is measured in HV5, HV10 or HV025 Adjustable shuttersIndentationDiamond indentor
  • 124. Vickers Hardness Test Machine4.11 4/23/2007 125 of 691
  • 125. Brinell Hardness Test 4.11 4/23/2007 126 of 691 • Hardened steel ball of given diameter is subjected for a given time to a given load • Load divided by area of indentation gives Brinell hardness in kg/mm2 • More suitable for on site hardness testing 30KN Ø=10mm steel ball
  • 126. Rockwell Hardness Test 4/23/2007 127 of 691 1KN Ø=1.6mm steel ball Rockwell B Rockwell C 1.5KN 120 Diamond Cone
  • 127. Hardness Testing 4.12 4/23/2007 128 of 691 Hardness Test Methods Typical Designations Vickers 240 HV10 Rockwell Rc 22 Brinell 200 BHN-W usually the hardest region 1.5 to 3mm HAZ fusion line or fusion boundary Hardness specimens can also be used for CTOD samples
  • 128. Crack Tip Opening Displacement testing 4.12 • Test is for fracture toughness • Square bar machined with a notch placed in the centre. • Tested below ambient temperature at a specified temperature. • Load is applied at either end of the test specimen in an attempt to open a crack at the bottom of the notch • Normally 3 samples 4/23/2007 129 of 691
  • 129. Fatigue Fracture4.13 4/23/2007 130 of 691 Location: Any stress concentration area Steel Type: All steel types Susceptible Microstructure: All grain structures Test for Fracture Toughness is CTOD (Crack Tip Opening Displacement)
  • 130. Fatigue Fracture4.13 4/23/2007 131 of 691 • Fatigue cracks occur under cyclic stress conditions • Fracture normally occurs at a change in section, notch and weld defects i.e stress concentration area • All materials are susceptible to fatigue cracking • Fatigue cracking starts at a specific point referred to as a initiation point • The fracture surface is smooth in appearance sometimes displaying beach markings • The final mode of failure may be brittle or ductile or a combination of both
  • 131. Fatigue Fracture 4/23/2007 132 of 691 • Toe grinding, profile grinding. • The elimination of poor profiles • The elimination of partial penetration welds and weld defects • Operating conditions under the materials endurance limits • The elimination of notch effects e.g. mechanical damage cap/root undercut • The selection of the correct material for the service conditions of the component Precautions against Fatigue Cracks
  • 132. Fatigue Fracture Fatigue fracture occurs in structures subject to repeated application of tensile stress. Crack growth is slow (in same cases, crack may grow into an area of low stress and stop without failure). 4/23/2007 133 of 691
  • 133. Fatigue Fracture 4/23/2007 134 of 691 Initiation points / weld defects Fatigue fracture surface smooth in appearance Secondary mode of failure ductile fracture rough fibrous appearance
  • 134. Fatigue Fracture • Crack growth is slow • It initiate from stress concentration points • load is considerably below the design or yield stress level • The surface is smooth • The surface is bounded by a curve • Bands may sometimes be seen on the smooth surface –”beachmarks”. They show the progress of the crack front from the point of origin • The surface is 90° to the load • Final fracture will usually take the form of gross yielding (as the maximum stress in the remaining ligament increase!) • Fatigue crack need initiation + propagation periods 4/23/2007 135 of 691 Fatigue fracture distinguish features:
  • 135. Bend Tests 4.15 4/23/2007 136 of 691 Object of test: • To determine the soundness of the weld zone. Bend testing can also be used to give an assessment of weld zone ductility. • There are three ways to perform a bend test: Root bend Face bend Side bend Side bend tests are normally carried out on welds over 12mm in thickness
  • 136. Bending test4.16 Types of bend test for welds (acc. BS EN 910): 4/23/2007 137 of 691 Thickness of material - “t” “t” up to 12 mm “t” over 12 mm Root / face bend Side bend
  • 137. Fillet Weld Fracture Tests 4.17 Object of test: • To break open the joint through the weld to permit examination of the fracture surfaces • Specimens are cut to the required length • A saw cut approximately 2mm in depth is applied along the fillet welds length • Fracture is usually made by striking the specimen with a single hammer blow • Visual inspection for defects 4/23/2007 138 of 691
  • 138. Fillet Weld Fracture Tests4.17 4/23/2007 139 of 691 Fracture should break weld saw cut to root 2mm Notch Hammer
  • 139. Fillet Weld Fracture Tests 4.17 4/23/2007 140 of 691 This fracture indicates lack of fusion This fracture has occurred saw cut to root Lack of Penetration
  • 140. Nick-Break Test4.18 Object of test: • To permit evaluation of any weld defects across the fracture surface of a butt weld. •Specimens are cut transverse to the weld •A saw cut approximately 2mm in depth is applied along the welds root and cap •Fracture is usually made by striking the specimen with a single hammer blow •Visual inspection for defects 4/23/2007 141 of 691
  • 141. Nick-Break Test4.18 4/23/2007 142 of 691 Approximately 230 mm 19 mm 2 mm 2 mm Notch cut by hacksaw Weld reinforcement may or may not be removed
  • 142. Nick Break Test 4.18 4/23/2007 143 of 691 Inclusions on fracture line Lack of root penetration or fusion Alternative nick-break test specimen, notch applied all way around the specimen
  • 143. 4/23/2007 144 of 691 We test welds to establish minimum levels of mechanical properties, and soundness of the welded joint We divide tests into Qualitative & Quantitative methods: Qualitative: (Have no units/numbers) For assessing joint quality Macro tests Bend tests Fillet weld fracture tests Butt Nick break tests Quantitative: (Have units/numbers) To measure mechanical properties Hardness (VPN & BHN) Toughness (Joules & ft.lbs) Strength (N/mm2 & PSI, MPa) Ductility / Elongation (E%) Summary of Mechanical Testing4.19
  • 144. Welding Inspector WPS – Welder Qualifications Section 5 4/23/2007 145 of 691
  • 145. 4/23/2007 146 of 691 Welding Procedure Qualification5.1 Question: What is the main reason for carrying out a Welding Procedure Qualification Test ? (What is the test trying to show ?) Answer: To show that the welded joint has the properties* that satisfy the design requirements (fit for purpose) * properties •mechanical properties are the main interest - always strength but toughness & hardness may be important for some applications •test also demonstrates that the weld can be made without defects
  • 146. Welding Procedures5.1 4/23/2007 147 of 691 Producing a welding procedure involves: • Planning the tasks • Collecting the data • Writing a procedure for use of for trial • Making a test welds • Evaluating the results • Approving the procedure • Preparing the documentation
  • 147. Welding Procedures 5.2 4/23/2007 148 of 691 In most codes reference is made to how the procedure are to be devised and whether approval of these procedures is required. The approach used for procedure approval depends on the code: Example codes: • AWS D.1.1: Structural Steel Welding Code • BS 2633: Class 1 welding of Steel Pipe Work • API 1104: Welding of Pipelines • BS 4515: Welding of Pipelines over 7 Bar Other codes may not specifically deal with the requirement of a procedure but may contain information that may be used in writing a weld procedure • EN 1011Process of Arc Welding Steels
  • 148. 4/23/2007 149 of 691 The welding engineer writes qualified Welding Procedure Specifications (WPS) for production welding Welding Procedure Qualification 5.3 Production welding conditions must remain within the range of qualification allowed by the WPQR (according to EN ISO 15614)
  • 149. 4/23/2007 150 of 691 Welding Procedure Qualification5.3 (according to EN Standards) welding conditions are called welding variables welding variables are classified by the EN ISO Standard as: •Essential variables •Non-essential variables •Additional variables Note: additional variables = ASME supplementary essential The range of qualification for production welding is based on the limits that the EN ISO Standard specifies for essential variables* (* and when applicable - the additional variables)
  • 150. 4/23/2007 151 of 691 Welding Procedure Qualification5.3 (according to EN Standards) WELDING ESSENTIAL VARIABLES Question: Why are some welding variables classified as essential ? Answer: A variable, that if changed beyond certain limits (specified by the Welding Standard) may have a significant effect on the properties* of the joint * particularly joint strength and ductility
  • 151. 4/23/2007 152 of 691 Welding Procedure Qualification5.3 (according to EN Standards) SOME TYPICAL ESSENTIAL VARIABLES • Welding Process • Post Weld Heat Treatment (PWHT) • Material Type • Electrode Type, Filler Wire Type (Classification) • Material Thickness • Polarity (AC, DC+ve / DC-ve) • Pre-Heat Temperature • Heat Input • Welding Position
  • 152. Welding Procedures5.3 Components of a welding procedure Parent material • Type (Grouping) • Thickness • Diameter (Pipes) • Surface condition) Welding process • Type of process (MMA, MAG, TIG, SAW etc) • Equipment parameters • Amps, Volts, Travel speed Welding Consumables • Type of consumable/diameter of consumable • Brand/classification • Heat treatments/ storage 4/23/2007 153 of 691
  • 153. Welding Procedures5.3 Components of a welding procedure Joint design •Edge preparation •Root gap, root face •Jigging and tacking •Type of baking Welding Position •Location, shop or site •Welding position e.g. 1G, 2G, 3G etc •Any weather precaution Thermal heat treatments •Preheat, temps •Post weld heat treatments e.g. stress relieving 4/23/2007 154 of 691
  • 154. Welding Procedures5.3 4/23/2007 155 of 691 Object of a welding procedure test To give maximum confidence that the welds mechanical and metallurgical properties meet the requirements of the applicable code/specification. Each welding procedure will show a range to which the procedure is approved (extent of approval) If a customer queries the approval evidence can be supplied to prove its validity
  • 155. Welding Procedures 4/23/2007 156 of 691 Summary of designations: pWPS: Preliminary Welding Procedure Specification (Before procedure approval) WPAR (WPQR): Welding Procedure Approval Record (Welding procedure Qualification record) WPS: Welding Procedure Specification (After procedure approval)
  • 156. 4/23/2007 157 of 691 Example: Welding Procedure Specification (WPS)
  • 157. Welder Qualification5.4 4/23/2007 158 of 691 Numerous codes and standards deal with welder qualification, e.g. BS EN 287. • Once the content of the procedure is approved the next stage is to approve the welders to the approved procedure. • A welders test know as a Welders Qualification Test (WQT). Object of a welding qualification test: • To give maximum confidence that the welder meets the quality requirements of the approved procedure (WPS). • The test weld should be carried out on the same material and same conditions as for the production welds.
  • 158. 4/23/2007 159 of 691 Welder Qualification 5.4 & 5.5 (according to EN Standards) Question: What is the main reason for qualifying a welder ? Answer: To show that he has the skill to be able to make production welds that are free from defects Note: when welding in accordance with a Qualified WPS
  • 159. 4/23/2007 160 of 691 The welder is allowed to make production welds within the range of qualification shown on the Certificate The range of qualification allowed for production welding is based on the limits that the EN Standard specifies for the welder qualification essential variables Welder Qualification 5.5 (according to EN 287 ) A Certificate may be withdrawn by the Employer if there is reason to doubt the ability of the welder, for example • a high repair rate • not working in accordance with a qualified WPS The qualification shall remain valid for 2 years provided there is certified confirmation of welding to the WPS in that time. A Welder‟s Qualification Certificate automatically expires if the welder has not used the welding process for 6 months or longer.
  • 160. 4/23/2007 161 of 691 Welding Engineer writes a preliminary Welding Procedure Specification (pWPS) for each test weld to be made • A welder makes a test weld in accordance with the pWPS • A welding inspector records all the welding conditions used for the test weld (referred to as the „as-run‟ conditions) An Independent Examiner/ Examining Body/ Third Party inspector may be requested to monitor the qualification process Welding Procedure Qualification5.7 (according to EN ISO 15614) The finished test weld is subjected to NDT in accordance with the methods specified by the EN ISO Standard - Visual, MT or PT & RT or UT
  • 161. 4/23/2007 162 of 691 Welding Procedure Qualification 5.7 Test weld is subjected to destructive testing (tensile, bend, macro) The Application Standard, or Client, may require additional tests such as impact tests, hardness tests (and for some materials - corrosion tests) (according to EN ISO 15614) A Welding Procedure Qualification Record (WPQR) is prepared giving details of: - • The welding conditions used for the test weld • Results of the NDT • Results of the destructive tests • The welding conditions that the test weld allows for production welding The Third Party may be requested to sign the WPQR as a true record
  • 162. Welder Qualification5.9 4/23/2007 163 of 691 (according to EN 287 ) An approved WPS should be available covering the range of qualification required for the welder approval. • The welder qualifies in accordance with an approved WPS • A welding inspector monitors the welding to make sure that the welder uses the conditions specified by the WPS EN Welding Standard states that an Independent Examiner, Examining Body or Third Party Inspector may be required to monitor the qualification process
  • 163. 4/23/2007 164 of 691 The finished test weld is subjected to NDT by the methods specified by the EN Standard - Visual, MT or PT & RT or UT The test weld may need to be destructively tested - for certain materials and/or welding processes specified by the EN Standard or the Client Specification Welder Qualification5.9 (according to EN 287 ) • A Welder‟s Qualification Certificate is prepared showing the conditions used for the test weld and the range of qualification allowed by the EN Standard for production welding • The Qualification Certificate is usually endorsed by a Third Party Inspector as a true record of the test
  • 164. Welder Qualification5.10 4/23/2007 165 of 691 Information that should be included on a welders test certificate are, which the welder should have or have access to a copy of ! • Welders name and identification number • Date of test and expiry date of certificate • Standard/code e.g. BS EN 287 • Test piece details • Welding process. • Welding parameters, amps, volts • Consumables, flux type and filler classification details • Sketch of run sequence • Welding positions • Joint configuration details • Material type qualified, pipe diameter etc • Test results, remarks • Test location and witnessed by • Extent (range) of approval
  • 166. Material Inspection One of the most important items to consider is Traceability. The materials are of little use if we can not, by use of an effective QA system trace them from specification and purchase order to final documentation package handed over to the Client. All materials arriving on site should be inspected for: • Size / dimensions • Condition • Type / specification In addition other elements may need to be considered depending on the materials form or shape 4/23/2007 168 of 691
  • 167. Pipe Inspection 4/23/2007 169 of 691 We inspect the condition (Corrosion, Damage, Wall thickness Ovality, Laminations & Seam) Specification Welded seam Size LP5 Other checks may need to be made such as: distortion tolerance, number of plates and storage.
  • 168. Plate Inspection 4/23/2007 170 of 691 Size We inspect the condition (Corrosion, Mechanical damage, Laps, Bands & Laminations) 5L Specification Other checks may need to be made such as: distortion tolerance, number of plates and storage.
  • 169. 4/23/2007 171 of 691 Parent Material Imperfections Lamination Mechanical damage Lap Segregation line Laminations are caused in the parent plate by the steel making process, originating from ingot casting defects. Segregation bands occur in the centre of the plate and are low melting point impurities such as sulphur and phosphorous. Laps are caused during rolling when overlapping metal does not fuse to the base material.
  • 172. 4/23/2007 174 of 691 Laminations Plate Lamination
  • 173. Welding Inspector Codes & Standards Section 7 4/23/2007 175 of 691
  • 174. Codes & Standards 4/23/2007 176 of 691 The 3 agencies generally identified in a code or standard: The customer, or client The manufacturer, or contractor The 3rd party inspection, or clients representative Codes often do not contain all relevant data, but may refer to other standards
  • 175. 4/23/2007 177 of 691 Standard/Codes/Specifications STANDARDS SPECIFICATIONS CODES Examples plate, pipe forgings, castings valves electrodes Examples pressure vessels bridges pipelines tanks
  • 176. Welding Inspector Welding Symbols Section 8 4/23/2007 178 of 691
  • 177. Weld symbols on drawings Advantages of symbolic representation: • simple and quick plotting on the drawing • does not over-burden the drawing • no need for additional view • gives all necessary indications regarding the specific joint to be obtained Disadvantages of symbolic representation: • used only for usual joints • requires training for properly understanding of symbols 4/23/2007 179 of 691
  • 178. Weld symbols on drawings The symbolic representation includes: • an arrow line • a reference line • an elementary symbol The elementary symbol may be completed by: • a supplementary symbol • a means of showing dimensions • some complementary indications 4/23/2007 180 of 691
  • 179. Dimensions 4/23/2007 181 of 691 In most standards the cross sectional dimensions are given to the left side of the symbol, and all linear dimensions are give on the right side Convention of dimensions a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length (min material thickness) BS EN ISO 22553 AWS A2.4 •In a fillet weld, the size of the weld is the leg length •In a butt weld, the size of the weld is based on the depth of the joint preparation
  • 180. 4/23/2007 182 of 691 A method of transferring information from the design office to the workshop is: The above information does not tell us much about the wishes of the designer. We obviously need some sort of code which would be understood by everyone. Most countries have their own standards for symbols. Some of them are AWS A2.4 & BS EN 22553 (ISO 2553) Please weld here Weld symbols on drawings
  • 181. 4/23/2007 183 of 691 Joints in drawings may be indicated: •by detailed sketches, showing every dimension •by symbolic representation Weld symbols on drawings
  • 182. Elementary Welding Symbols (BS EN ISO 22553 & AWS A2.4) Convention of the elementary symbols: Various categories of joints are characterised by an elementary symbol. The vertical line in the symbols for a fillet weld, single/double bevel butts and a J-butt welds must always be on the left side. 4/23/2007 184 of 691 Square edge butt weld Weld type Sketch Symbol Single-v butt weld
  • 183. Elementary Welding Symbols 4/23/2007 185 of 691 Single-V butt weld with broad root face Weld type Sketch Symbol Single bevel butt weld Single bevel butt weld with broad root face Backing run
  • 184. Elementary Welding Symbols 4/23/2007 186 of 691 Single-U butt weld Weld type Sketch Symbol Single-J butt weld Fillet weld Surfacing
  • 185. ISO 2553 / BS EN 22553 4/23/2007 187 of 691 Plug weld Resistance spot weld Resistance seam weld Square Butt weld Steep flanked Single-V Butt Surfacing
  • 186. 4/23/2007 188 of 691 Arrow Line (BS EN ISO 22553 & AWS A2.4): Convention of the arrow line: • Shall touch the joint intersection • Shall not be parallel to the drawing • Shall point towards a single plate preparation (when only one plate has preparation)
  • 187. 4/23/2007 189 of 691 (AWS A2.4) Convention of the reference line: Shall touch the arrow line Shall be parallel to the bottom of the drawing Reference Line
  • 188. 4/23/2007 190 of 691 or Reference Line (BS EN ISO 22553) Convention of the reference line: • Shall touch the arrow line • Shall be parallel to the bottom of the drawing • There shall be a further broken identification line above or beneath the reference line (Not necessary where the weld is symmetrical!)
  • 189. 4/23/2007 191 of 691 (BS EN ISO 22553 & AWS A2.4) Convention of the double side weld symbols: Representation of welds done from both sides of the joint intersection, touched by the arrow head Fillet weld Double V Double bevel Double U Double J Double side weld symbols
  • 190. ISO 2553 / BS EN 22553 4/23/2007 192 of 691 Arrow line Reference lines Arrow side Other side Arrow side Other side
  • 191. ISO 2553 / BS EN 22553 4/23/2007 193 of 691 Single-V Butt flush cap Single-U Butt with sealing run Single-V Butt with permanent backing strip M Single-U Butt with removable backing strip M R
  • 192. ISO 2553 / BS EN 22553 4/23/2007 194 of 691 Single-bevel butt Double-bevel butt Single-bevel butt Single-J butt
  • 193. ISO 2553 / BS EN 22553 4/23/2007 195 of 691 Partial penetration single-V butt „S‟ indicates the depth of penetration s10 10 15
  • 194. ISO 2553 / BS EN 22553 4/23/2007 196 of 691 a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length(min material thickness) a = (0.7 x z) a 4 4mm Design throat z 6 6mm leg a z s s 6 6mm Actual throat
  • 195. ISO 2553 / BS EN 22553 4/23/2007 197 of 691 Arrow side Arrow side
  • 196. ISO 2553 / BS EN 22553 4/23/2007 198 of 691 Other side Other side s6 s6 6mm fillet weld
  • 197. ISO 2553 / BS EN 22553 4/23/2007 199 of 691 n = number of weld elements l = length of each weld element (e) = distance between each weld element n x l (e) Welds to be staggered Process 2 x 40 (50) 3 x 40 (50) 111
  • 198. ISO 2553 / BS EN 22553 4/23/2007 200 of 691 80 80 80 909090 6 6 5 5 z5 z6 3 x 80 (90) 3 x 80 (90) All dimensions in mm
  • 199. ISO 2553 / BS EN 22553 4/23/2007 201 of 691 All dimensions in mm 8 8 6 6 80 80 80 909090 z8 z6 3 x 80 (90) 3 x 80 (90)
  • 200. 4/23/2007 202 of 691 Supplementary symbols Concave or Convex Toes to be ground smoothly (BS EN only) Site Weld Weld all round (BS EN ISO 22553 & AWS A2.4) Convention of supplementary symbols Supplementary information such as welding process, weld profile, NDT and any special instructions
  • 201. 4/23/2007 203 of 691 Supplementary symbols Further supplementary information, such as WPS number, or NDT may be placed in the fish tail Ground flush 111 Welding process numerical BS EN MR Removable backing strip Permanent backing strip M (BS EN ISO 22553 & AWS A2.4) Convention of supplementary symbols Supplementary information such as welding process, weld profile, NDT and any special instructions
  • 202. ISO 2553 / BS EN 22553 4/23/2007 204 of 691 ba dc
  • 203. ISO 2553 / BS EN 22553 4/23/2007 205 of 691 ConvexMitre Toes shall be blended Concave
  • 204. ISO 2553 / BS EN 22553 4/23/2007 206 of 691 a = Design throat thickness s = Depth of Penetration, Throat thickness z = Leg length(min material thickness) a = (0.7 x z) a 4 4mm Design throat z 6 6mm leg a z s s 6 6mm Actual throat
  • 205. ISO 2553 / BS EN 22553 Complimentary Symbols 4/23/2007 207 of 691 Field weld (site weld) The component requires NDT inspection WPS Additional information, the reference document is included in the box Welding to be carried out all round component (peripheral weld) NDT
  • 206. ISO 2553 / BS EN 22553 4/23/2007 208 of 691 Numerical Values for Welding Processes: 111: MMA welding with covered electrode 121: Sub-arc welding with wire electrode 131: MIG welding with inert gas shield 135: MAG welding with non-inert gas shield 136: Flux core arc welding 141: TIG welding 311: Oxy-acetylene welding 72: Electro-slag welding 15: Plasma arc welding
  • 207. AWS A2.4 Welding Symbols 4/23/2007 209 of 691
  • 208. AWS Welding Symbols 4/23/2007 210 of 691 1(1-1/8) 60o 1/8 Depth of Bevel Effective Throat Root Opening Groove Angle
  • 209. AWS Welding Symbols 4/23/2007 211 of 691 1(1-1/8) 60o 1/8 GSFCAW Welding Process GMAW GTAW SAW
  • 210. AWS Welding Symbols 4/23/2007 212 of 691 3 – 10 3 – 10 Welds to be staggered SMAW Process 10 3 3
  • 211. AWS Welding Symbols 4/23/2007 213 of 691 1(1-1/8) 60o 1/8 FCAW Sequence of Operations 1st Operation 2nd Operation 3rd Operation
  • 212. AWS Welding Symbols 4/23/2007 214 of 691 1(1-1/8) 60o 1/8 FCAW Sequence of Operations RT MT MT
  • 213. AWS Welding Symbols 4/23/2007 215 of 691 Dimensions- Leg Length 6/8 6 leg on member A 8 6Member A Member B
  • 214. Welding Inspector Intro To Welding Processes Section 9 4/23/2007 221 of 691
  • 215. Welding Processes 4/23/2007 222 of 691 Welding is regarded as a joining process in which the work pieces are in atomic contact Pressure welding • Forge welding • Friction welding • Resistance Welding Fusion welding • Oxy-acetylene • MMA (SMAW) • MIG/MAG (GMAW) • TIG (GTAW) • Sub-arc (SAW) • Electro-slag (ESW) • Laser Beam (LBW) • Electron-Beam (EBW)
  • 216. 4/23/2007 225 of 691 20 8040 60 130 140120100 180160 200 10 60 50 40 30 20 80 70 90 100 Normal Operating Voltage Range Large voltage variation, e.g. + 10v (due to changes in arc length) Small amperage change resulting in virtually constant current e.g. + 5A. Voltage Amperage Required for: MMA, TIG, Plasma arc and SAW > 1000 AMPS O.C.V. Striking voltage (typical) for arc initiation Constant Current Power Source (Drooping Characteristic)
  • 217. Monitoring Heat Input • Heat Input: The amount of heat generated in the welding arc per unit length of weld. Expressed in kilo Joules per millimetre length of weld (kJ/mm). Heat Input (kJ/mm)= Volts x Amps Travel speed(mm/s) x 1000 4/23/2007 227 of 691
  • 218. Monitoring Heat Input 4/23/2007 228 of 691 Weld and weld pool temperatures
  • 220. Monitoring Heat Input • Monitoring Heat Input As Required by • BS EN ISO 15614-1:2004 • In accordance with EN 1011-1:1998 4/23/2007 230 of 691 When impact requirements and/or hardness requirements are specified, impact test shall be taken from the weld in the highest heat input position and hardness tests shall be taken from the weld in the lowest heat input position in order to qualify for all positions
  • 221. Welding Inspector MMA Welding Section 10 4/23/2007 231 of 691
  • 222. MMA - Principle of operation 4/23/2007 233 of 691
  • 223. MMA welding Main features: • Shielding provided by decomposition of flux covering • Electrode consumable • Manual process Welder controls: • Arc length • Angle of electrode • Speed of travel • Amperage settings 4/23/2007 234 of 691
  • 224. Manual Metal Arc Basic Equipment 4/23/2007 235 of 691 Power source Holding oven Inverter power source Electrode holder Power cables Welding visor filter glass Return lead Electrodes Electrode oven Control panel (amps, volts)
  • 225. MMA Welding Plant 4/23/2007 236 of 691 Transformer: • Changes mains supply voltage to a voltage suitable for welding. Has no moving parts and is often termed static plant. Rectifier: • Changes a.c. to d.c., can be mechanically or statically achieved. Generator: • Produces welding current. The generator consists of an armature rotating in a magnetic field, the armature must be rotated at a constant speed either by a motor unit or, in the absence of electrical power, by an internal combustion engine. Inverter: • An inverter changes d.c. to a.c. at a higher frequency.
  • 226. MMA Welding Variables 4/23/2007 237 of 691 Voltage • The arc voltage in the MMA process is measured as close to the arc as possible. It is variable with a change in arc length O.C.V. • The open circuit voltage is the voltage required to initiate, or re-ignite the electrical arc and will change with the type of electrode being used e.g 70-90 volts Current • The current used will be determined by the choice of electrode, electrode diameter and material type and thickness. Current has the most effect on penetration. Polarity • Polarity is generally determined by operation and electrode type e.g DC +ve, DC –ve or AC
  • 227. 4/23/2007 239 of 691 20 8040 60 130 140120100 180160 200 10 60 50 40 30 20 80 70 90 100 Normal Operating Voltage Range Large voltage variation, e.g. + 10v (due to changes in arc length) Small amperage change resulting in virtually constant current e.g. + 5A. Voltage Amperage O.C.V. Striking voltage (typical) for arc initiation Constant Current Power Source (Drooping Characteristic)
  • 228. MMA welding parameters Travel speed 4/23/2007 240 of 691 Travel speed Too highToo low •wide weld bead contour •lack of penetration •burn-through •lack of root fusion •incomplete root penetration •undercut •poor bead profile, difficult slag removal
  • 229. MMA welding parameters Type of current: • voltage drop in welding cables is lower with AC • inductive looses can appear with AC if cables are coiled • cheaper power source for AC • no problems with arc blow with AC • DC provides a more stable and easy to strike arc, especially with low current, better positional weld, thin sheet applications • welding with a short arc length (low arc voltage) is easier with DC, better mechanical properties • DC provides a smoother metal transfer, less spatter 4/23/2007 241 of 691
  • 230. MMA welding parameters Welding current 4/23/2007 242 of 691 – approx. 35 A/mm of diameter – governed by thickness, type of joint and welding position Welding current Too highToo low •poor starting •slag inclusions •weld bead contour too high •lack of fusion/penetration •spatter •excess penetration •undercut •burn-through
  • 231. MMA welding parameters Arc length = arc voltage 4/23/2007 243 of 691 Arc voltage Too highToo low •arc can be extinguished •“stubbing” •spatter •porosity •excess penetration •undercut •burn-through Polarity: DCEP generally gives deeper penetration
  • 232. MMA - Troubleshooting 4/23/2007 244 of 691 MMA quality (left to right) current, arc length and travel speed normal; current too low; current too high; arc length too short; arc length too long; travel speed too slow; travel speed too high
  • 233. MMA electrode holder 4/23/2007 245 of 691 Collet or twist type “Tongs” type with spring-loaded jaws
  • 234. MMA Welding Consumables 4/23/2007 246 of 691 The three main electrode covering types used in MMA welding • Cellulosic - deep penetration/fusion • Rutile - general purpose • Basic - low hydrogen (Covered in more detail in Section 14) MMA Covered Electrodes
  • 235. 4/23/2007 247 of 691 Most welding defects in MMA are caused by a lack of welder skill (not an easily controlled process), the incorrect settings of the equipment, or the incorrect use, and treatment of electrodes Typical Welding Defects: •Slag inclusions •Arc strikes •Porosity •Undercut •Shape defects (overlap, excessive root penetration, etc.) MMA welding typical defects
  • 236. Manual Metal Arc Welding (MMA) 4/23/2007 248 of 691 Advantages: • Field or shop use • Range of consumables • All positions • Portable • Simple equipment Disadvantages: • High welder skill required • High levels of fume • Hydrogen control (flux) • Stop/start problems • Comparatively uneconomic when compared with some other processes i.e MAG, SAW and FCAW
  • 237. Welding Inspector TIG Welding Section 11 4/23/2007 249 of 691
  • 238. Tungsten Inert Gas Welding 4/23/2007 250 of 691 The TIG welding process was first developed in the USA during the 2nd world war for the welding of aluminum alloys • The process uses a non-consumable tungsten electrode • The process requires a high level of welder skill • The process produces very high quality welds. • The TIG process is considered as a slow process compared to other arc welding processes • The arc may be initiated by a high frequency to avoid scratch starting, which could cause contamination of the tungsten and weld
  • 239. TIG - Principle of operation 4/23/2007 251 of 691
  • 240. TIG Welding Variables 4/23/2007 254 of 691 Voltage The voltage of the TIG welding process is variable only by the type of gas being used, and changes in the arc length Current The current is adjusted proportionally to the tungsten electrodes diameter being used. The higher the current the deeper the penetration and fusion Polarity The polarity used for steels is always DC –ve as most of the heat is concentrated at the +ve pole, this is required to keep the tungsten electrode at the cool end of the arc. When welding aluminium and its alloys AC current is used
  • 241. Types of current • can be DCEN or DCEP • DCEN gives deep penetration • requires special power source • low frequency - up to 20 pulses/sec (thermal pulsing) • better weld pool control • weld pool partially solidifies between pulses4/23/2007 256 of 691 Type of welding current can be sine or square wave requires a HF current (continuos or periodical) provide cleaning action DC AC Pulsed current
  • 242. Choosing the proper electrode Current type influence 4/23/2007 257 of 691 + + + + + + + + + - - - - - - - - - Electrode capacity Current type & polarity Heat balance Oxide cleaning action Penetration DCEN DCEPAC (balanced) 70% at work 30% at electrode 50% at work 50% at electrode 35% at work 65% at electrode Deep, narrow Medium Shallow, wide No Yes - every half cycle Yes Excellent (e.g. 3,2 mm/400A) Good (e.g. 3,2 mm/225A) Poor (e.g. 6,4 mm/120A)
  • 243. ARC CHARACTERISTICS 4/23/2007 258 of 691 Volts Amps OCV Constant Current/Amperage Characteristic Large change in voltage = Smaller change in amperage Welding Voltage Large arc gap Small arc gap
  • 244. TIG - arc initiation methods • simple method • tungsten electrode is in contact with the workpiece! • high initial arc current due to the short circuit • impractical to set arc length in advance • electrode should tap the workpiece - no scratch! • ineffective in case of AC • used when a high quality is not essential 4/23/2007 259 of 691 Arc initiation method Lift arc HF start need a HF generator (spark- gap oscillator) that generates a high voltage AC output (radio frequency) costly reliable method required on both DC (for start) and AC (to re-ignite the arc) can be used remotely HF produce interference requires superior insulation
  • 245. Pulsed current • usually peak current is 2-10 times background current • useful on metals sensitive to high heat input • reduced distortions • in case of dissimilar thicknesses equal penetration can be achieved 4/23/2007 260 of 691 Time Current(A) Pulse time Cycle time Peak current Background current Average current one set of variables can be used in all positions used for bridging gaps in open root joints require special power source
  • 246. Choosing the proper electrode Polarity Influence – cathodic cleaning effect 4/23/2007 261 of 691
  • 247. Tungsten Electrodes 4/23/2007 262 of 691 Old types: (Slightly Radioactive) • Thoriated: DC electrode -ve - steels and most metals • 1% thoriated + tungsten for higher current values • 2% thoriated for lower current values • Zirconiated: AC - aluminum alloys and magnesium New types: (Not Radioactive) • Cerium: DC electrode -ve - steels and most metals • Lanthanum: AC - Aluminum alloys and magnesium
  • 248. TIG torch set-up • Electrode extension 4/23/2007 263 of 691 Electrode extension Stickout 2-3 times electrode diameter Electrode extension Low electron emission Unstable arc Too small Overheating Tungsten inclusions Too large
  • 249. Choosing the correct electrode Polarity Influence – cathodic cleaning effect 4/23/2007 264 of 691
  • 250. Tungsten Electrodes 4/23/2007 265 of 691 Old types: (Slightly Radioactive) • Thoriated: DC electrode -ve - steels and most metals • 1% thoriated + tungsten for higher current values • 2% thoriated for lower current values • Zirconiated: AC - aluminum alloys and magnesium New types: (Not Radioactive) • Cerium: DC electrode -ve - steels and most metals • Lanthanum: AC - Aluminum alloys and magnesium
  • 251. Tungsten electrode types 4/23/2007 266 of 691 Pure tungsten electrodes: colour code - green no alloy additions low current carrying capacity maintains a clean balled end can be used for AC welding of Al and Mg alloys poor arc initiation and arc stability with AC compared with other electrode types used on less critical applications low cost
  • 252. Tungsten electrode types 4/23/2007 267 of 691 Thoriated tungsten electrodes: colour code - yellow/red/violet 20% higher current carrying capacity compared to pure tungsten electrodes longer life - greater resistance to contamination thermionic - easy arc initiation, more stable arc maintain a sharpened tip recommended for DCEN, seldom used on AC (difficult to maintain a balled tip) This slightly radioactive
  • 253. Tungsten electrode types 4/23/2007 268 of 691 Ceriated tungsten electrodes: colour code - grey (orange acc. AWS A-5.12) operate successfully with AC or DC Ce not radioactive - replacement for thoriated types Lanthaniated tungsten electrodes: colour code - black/gold/blue operating characteristics similar with ceriated electrode
  • 254. Tungsten electrode types 4/23/2007 269 of 691 Zirconiated tungsten electrodes: colour code - brown/white operating characteristics fall between those of pure and thoriated electrodes retains a balled end during welding - good for AC welding high resistance to contamination preferred for radiographic quality welds
  • 255. Electrode tip for DCEN 4/23/2007 270 of 691 Electrode tip prepared for low current welding Electrode tip prepared for high current welding Vertex angle Penetration increase Increase Bead width increase Decrease 2-2,5times electrodediameter
  • 256. Electrode tip for AC 4/23/2007 271 of 691 Electrode tip ground Electrode tip ground and then conditioned DC -ve AC
  • 257. TIG Welding Variables 4/23/2007 272 of 691 Tungsten electrodes The electrode diameter, type and vertex angle are all critical factors considered as essential variables. The vertex angle is as shown Vetex angle Note: when welding aluminium with AC current, the tungsten end is chamfered and forms a ball end when welding DC -ve Note: too fine an angle will promote melting of the electrodes tip AC
  • 258. Choosing the proper electrode 4/23/2007 273 of 691 Unstable arc Tungsten inclusions Welding current Electrode tip not properly heated Excessive melting or volatilisation Too low Too high Factors to be considered: Penetration
  • 259. Shielding gas requirements • Preflow and postflow 4/23/2007 275 of 691 Preflow Postflow Shielding gas flow Welding current Flow rate too low Flow rate too high
  • 260. Special shielding methods 4/23/2007 276 of 691 Pipe root run shielding – Back Purging to prevent excessive oxidation during welding, normally argon.
  • 261. TIG torch set-up Electrode extension 4/23/2007 277 of 691 Electrode extension Stickout 2-3 times electrode diameter Electrode extension Low electron emission Unstable arc Too small Overheating Tungsten inclusions Too large
  • 262. TIG Welding Consumables Welding consumables for TIG: •Filler wires, Shielding gases, tungsten electrodes (non- consumable). •Filler wires of different materials composition and variable diameters available in standard lengths, with applicable code stamped for identification •Steel Filler wires of very high quality, with copper coating to resist corrosion. •shielding gases mainly Argon and Helium, usually of highest purity (99.9%). 4/23/2007 278 of 691
  • 263. Tungsten Inclusion 4/23/2007 279 of 691 A Tungsten Inclusion always shows up as bright white on a radiograph May be caused by Thermal Shock of heating to fast and small fragments break off and enter the weld pool, so a “slope up” device is normally fitted to prevent this could be caused by touch down also. Most TIG sets these days have slope- up devices that brings the current to the set level over a short period of time so the tungsten is heated more slowly and gently
  • 264. 4/23/2007 280 of 691 Most welding defects with TIG are caused by a lack of welder skill, or incorrect setting of the equipment. i.e. current, torch manipulation, welding speed, gas flow rate, etc. • Tungsten inclusions (low skill or wrong vertex angle) • Surface porosity (loss of gas shield mainly on site) • Crater pipes (bad weld finish technique i.e. slope out) • Oxidation of S/S weld bead, or root by poor gas cover • Root concavity (excess purge pressure in pipe) • Lack of penetration/fusion (widely on root runs) TIG typical defects
  • 265. Tungsten Inert Gas Welding Advantages • High quality • Good control • All positions • Lowest H2 process • Minimal cleaning • Autogenous welding (No filler material) • Can be automated Disadvantages • High skill factor required • Low deposition rate • Small consumable range • High protection required • Complex equipment • Low productivity • High ozone levels +HF 4/23/2007 281 of 691
  • 266. Welding Inspector MIG/MAG Welding Section 12 4/23/2007 282 of 691
  • 267. Gas Metal Arc Welding 4/23/2007 283 of 691 The MIG/MAG welding process was initially developed in the USA in the late 1940s for the welding of aluminum alloys. The latest EN Welding Standards now refer the process by the American term GMAW (Gas Metal Arc Welding) • The process uses a continuously fed wire electrode • The weld pool is protected by a separately supplied shielding gas • The process is classified as a semi-automatic welding process but may be fully automated • The wire electrode can be either bare/solid wire or flux cored hollow wire
  • 268. MIG/MAG - Principle of operation 4/23/2007 284 of 691
  • 269. MIG/MAG process variables • Welding current • Polarity 4/23/2007 286 of 691 •Increasing welding current •Increase in depth and width •Increase in deposition rate
  • 270. MIG/MAG process variables • Arc voltage • Travel speed 4/23/2007 287 of 691 •Increasing travel speed •Reduced penetration and width, undercut •Increasing arc voltage •Reduced penetration, increased width •Excessive voltage can cause porosity, spatter and undercut
  • 271. Gas Metal Arc Welding 4/23/2007 289 of 691 Types of Shielding Gas MIG (Metal Inert Gas) • Inert Gas is required for all non-ferrous alloys (Al, Cu, Ni) • Most common inert gas is Argon • Argon + Helium used to give a „hotter‟ arc - better for thicker joints and alloys with higher thermal conductivity
  • 272. MIG/MAG – shielding gases 4/23/2007 290 of 691 Type of material Shielding gas Carbon steel Stainless steel Aluminium CO2 , Ar+(5-20)%CO2 Ar+2%O2 Ar
  • 273. MIG/MAG shielding gases Argon (Ar): higher density than air; low thermal conductivity the arc has a high energy inner cone; good wetting at the toes; low ionisation potential Helium (He): lower density than air; high thermal conductivity uniformly distributed arc energy; parabolic profile; high ionisation potential Carbon Dioxide (CO2): cheap; deep penetration profile; cannot support spray transfer; poor wetting; high spatter 4/23/2007 291 of 691 Ar Ar-He He CO2
  • 274. MIG/MAG shielding gases Gases for dip transfer: • CO2: carbon steels only: deep penetration; fast welding speed; high spatter levels • Ar + up to 25% CO2: carbon and low alloy steels: minimum spatter; good wetting and bead contour • 90% He + 7.5% Ar + 2.5% CO2:stainless steels: minimises undercut; small HAZ • Ar: Al, Mg, Cu, Ni and their alloys on thin sections • Ar + He mixtures: Al, Mg, Cu, Ni and their alloys on thicker sections (over 3 mm) 4/23/2007 292 of 691
  • 275. MIG/MAG shielding gases Gases for spray transfer • Ar + (5-18)% CO2: carbon steels: minimum spatter; good wetting and bead contour • Ar + 2% O2: low alloy steels: minimise undercut; provides good toughness • Ar + 2% O2 or CO2: stainless steels: improved arc stability; provides good fusion • Ar: Al, Mg, Cu, Ni, Ti and their alloys • Ar + He mixtures: Al, Cu, Ni and their alloys: hotter arc than pure Ar to offset heat dissipation • Ar + (25-30)% N2: Cu alloys: greater heat input 4/23/2007 293 of 691
  • 276. Gas Metal Arc Welding Types of Shielding Gas MAG (Metal Active Gas) • Active gases used are Oxygen and Carbon Dioxide • Argon with a small % of active gas is required for all steels (including stainless steels) to ensure a stable arc & good droplet wetting into the weld pool • Typical active gases are Ar + 20% CO2 for C-Mn & low alloy steels Ar + 2% O2 for stainless steels 100% CO2 can be used for C - steels 4/23/2007 294 of 691
  • 277. MIG/MAG Gas Metal Arc Welding Electrode orientation 4/23/2007 295 of 691 Penetration Deep Moderate Shallow Excess weld metal Maximum Moderate Minimum Undercut Severe Moderate Minimum Electrode extension •Increased extension
  • 278. MIG / MAG - self-regulating arc 4/23/2007 296 of 691 Stable condition Sudden change in gun position L 19 mm 25 mmL‟ Arc length L = 6,4 mm Arc voltage = 24V Welding current = 250A WFS = 6,4 m/min Melt off rate = 6,4 m/min Arc length L‟ = 12,7 mm Arc voltage = 29V Welding current = 220A WFS = 6,4 m/min Melt off rate = 5,6 m/min Current (A) Voltage(V)
  • 279. MIG/MAG - self-regulating arc 4/23/2007 297 of 691 Sudden change in gun position 25 mmL‟ Arc length L‟ = 12,7 mm Arc voltage = 29V Welding current = 220A WFS = 6,4 m/min Melt off rate = 5,6 m/min Current (A) Voltage(V) Re-established stable condition 25 mm L Arc length L = 6,4 mm Arc voltage = 24V Welding current = 250A WFS = 6,4 m/min Melt off rate = 6,4 m/min
  • 280. Terminating the arc • Burnback time 4/23/2007 298 of 691 – delayed current cut-off to prevent wire freeze in the weld end crater – depends on WFS (set as short as possible!) Contact tip Workpiec e Burnback time 0.05 sec 0.10 sec 0.15 sec 14 mm 8 mm 3 mm Current - 250A Voltage - 27V WFS - 7,8 m/min Wire diam. - 1,2 mm Shielding gas - Ar+18%CO2 Insulatin g slag Crater fill
  • 281. MIG/MAG - metal transfer modes Set-up for dip transfer Set-up for spray transfer 4/23/2007 299 of 691 Electrode extension 19-25 mm Contact tip recessed (3-5 mm) Contact tip extension (0-3,2 mm) Electrode extension 6-13 mm
  • 282. MIG/MAG - metal transfer modes Current/voltage conditions4/23/2007 301 of 691 Current Voltage Dip transfer Spray transfer Globular transfer Electrode diameter = 1,2 mm WFS = 3,2 m/min Current = 145 A Voltage = 18-20V Electrode diameter = 1,2 mm WFS = 8,3 m/min Current = 295 A Voltage = 28V
  • 283. MIG/MAG-methods of metal transfer 4/23/2007 303 of 691 Dip transfer Transfer occur due to short circuits between wire and weld pool, high level of spatter, need inductance control to limit current raise Can use pure CO2 or Ar- CO2 mixtures as shielding gas Metal transfer occur when arc is extinguished Requires low welding current/arc voltage, a low heat input process. Resulting in low residual stress and distortion Used for thin materials and all position welds
  • 284. MIG/MAG-methods of metal transfer 4/23/2007 306 of 691 Spray transfer Transfer occur due to pinch effect NO contact between wire and weld pool! Requires argon-rich shielding gas Metal transfer occur in small droplets, a large volume weld pool Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion Used for thick materials and flat/horizontal position welds
  • 285. MIG/MAG-methods of metal transfer 4/23/2007 307 of 691 Pulsed transfer Controlled metal transfer, one droplet per pulse, No transfer between droplet and weld pool! Requires special power sources Metal transfer occur in small droplets (diameter equal to that of electrode) Requires moderate welding current/arc voltage, a reduced heat input . Resulting in smaller residual stress and distortion compared to spray transfer Pulse frequency controls the volume of weld pool, used for root runs and out of position welds
  • 286. MIG/MAG - metal transfer modes Pulsed transfer 4/23/2007 308 of 691 Controlled metal transfer. one droplet per pulse. NO transfer during background current! Requires special power sources Metal transfer occur in small droplets (diameter equal to that of electrode) Requires moderate welding current/arc voltage, reduced heat input‟ smaller residual stress and distortions compared to spray transfer Pulse frequency controls the volume of weld pool, used for root runs and out of position welds
  • 287. MIG/MAG-methods of metal transfer 4/23/2007 310 of 691 Globular transfer Transfer occur due to gravity or short circuits between drops and weld pool Requires CO2 shielding gas Metal transfer occur in large drops (diameter larger than that of electrode) hence severe spatter Requires high welding current/arc voltage, a high heat input process. Resulting in high residual stress and distortion Non desired mode of transfer!
  • 288. 4/23/2007 315 of 691 O.C.V. Arc Voltage Virtually no Change. Voltage Flat or Constant Voltage Characteristic Used With MIG/MAG, ESW & SAW < 1000 amps 100 200 300 33 32 31 Large Current Change Small Voltage Change. Amperage Flat or Constant Voltage Characteristic
  • 289. MIG/MAG welding gun assembly 4/23/2007 316 of 691 Contact tip Gas diffuser Handle Gas nozzle Trigger WFS remote control potentiometer Union nut The Push-Pull gun
  • 290. Gas Metal Arc Welding 4/23/2007 318 of 691 PROCESS CHARACTERISTICS • Requires a constant voltage power source, gas supply, wire feeder, welding torch/gun and „hose package‟ • Wire is fed continuously through the conduit and is burnt-off at a rate that maintains a constant arc length/arc voltage • Wire feed speed is directly related to burn-off rate • Wire burn-off rate is directly related to current • When the welder holds the welding gun the process is said to be a semi-automatic process • The process can be mechanised and also automated • In Europe the process is usually called MIG or MAG
  • 291. 4/23/2007 322 of 691 Most welding imperfections in MIG/MAG are caused by lack of welder skill, or incorrect settings of the equipment •Worn contact tips will cause poor power pick up, or transfer •Bad power connections will cause a loss of voltage in the arc •Silica inclusions (in Fe steels) due to poor inter-run cleaning •Lack of fusion (primarily with dip transfer) •Porosity (from loss of gas shield on site etc) •Solidification problems (cracking, centerline pipes, crater pipes) especially on deep narrow welds MIG/MAG typical defects
  • 292. WELDING PROCESS 4/23/2007 323 of 691 Flux Core Arc Welding (Not In The Training Manual)
  • 293. Flux cored arc welding 4/23/2007 324 of 691 FCAW methods With gas shielding - “Outershield” Without gas shielding - “Innershield” With metal powder - “Metal core”
  • 294. “Outershield” - principle of operation 4/23/2007 325 of 691
  • 295. “Innershield” - principle of operation 4/23/2007 326 of 691
  • 296. ARC CHARACTERISTICS 4/23/2007 327 of 691 Volts Amps OCV Constant Voltage Characteristic Small change in voltage = large change in amperage The self adjusting arc. Large arc gap Small arc gap
  • 297. 4/23/2007 328 of 691 Insulated extension nozzle Current carrying guild tube Flux cored hollow wire Flux powder Arc shield composed of vaporized and slag forming compounds Metal droplets covered with thin slag coating Molten weld poolSolidified weld metal and slag Flux core Wire joint Flux core wires Flux Core Arc Welding (FCAW)
  • 298. Flux cored arc welding 4/23/2007 329 of 691 FCAW methods With gas shielding - “Outershield” Without gas shielding - “Innershield” (114) With metal powder - “Metal core” With active gas shielding (136) With inert gas shielding (137)
  • 299. FCAW - differences from MIG/MAG • usually operates in DCEP but some “Innershield” wires operates in DCEN • power sources need to be more powerful due to the higher currents • doesn't work in deep transfer mode • require knurled feed rolls 4/23/2007 330 of 691 “Innershield” wires use a different type of welding gun
  • 300. Backhand (“drag”) technique Advantages 4/23/2007 331 of 691 preferred method for flat or horizontal position slower progression of the weld deeper penetration weld stays hot longer, easy to remove dissolved gasses Disadvantages produce a higher weld profile difficult to follow the weld joint can lead to burn-through on thin sheet plates
  • 301. Forehand (“push”) technique Advantages 4/23/2007 332 of 691 preferred method for vertical up or overhead position arc is directed towards the unwelded joint , preheat effect easy to follow the weld joint and control the penetration Disadvantages produce a low weld profile, with coarser ripples fast weld progression, shallower depth of penetration the amount of spatter can increase
  • 302. FCAW advantages • less sensitive to lack of fusion • requires smaller included angle compared to MMA • high productivity • all positional • smooth bead surface, less danger of undercut • basic types produce excellent toughness properties • good control of the weld pool in positional welding especially with rutile wires • seamless wires have no torsional strain, twist free • ease of varying the alloying constituents • no need for shielding gas 4/23/2007 333 of 691
  • 303. FCAW disadvantages • limited to steels and Ni-base alloys • slag covering must be removed • FCAW wire is more expensive on a weight basis than solid wires (exception: some high alloy steels) • for gas shielded process, the gaseous shield may be affected by winds and drafts • more smoke and fumes are generated compared with MIG/MAG • in case of Innershield wires, it might be necessary to break the wire for restart (due to the high amount of insulating slag formed at the tip of the wire) 4/23/2007 334 of 691
  • 304. 4/23/2007 335 of 691 Advantages: 1) Field or shop use 2) High productivity 3) All positional 4) Slag supports and shapes the weld Bead 5) No need for shielding gas Disadvantages: 1) High skill factor 2) Slag inclusions 3) Cored wire is Expensive 4) High level of fume (Inner-shield) 5) Limited to steels and nickel alloys FCAW advantages/disadvantages
  • 305. Welding Inspector Submerged Arc Welding Section 13 4/23/2007 336 of 691
  • 306. 4/23/2007 337 of 691 • Submerged arc welding was developed in the Soviet Union during the 2nd world war for the welding of thick section steel. • The process is normally mechanized. • The process uses amps in the range of 100 to over 2000, which gives a very high current density in the wire producing deep penetration and high dilution welds. • A flux is supplied separately via a flux hopper in the form of either fused or agglomerated. • The arc is not visible as it is submerged beneath the flux layer and no eye protection is required. Submerged Arc Welding Introduction
  • 307. SAW Principle of operation 4/23/2007 338 of 691
  • 308. Principles of operation 4/23/2007 339 of 691 Factors that determine whether to use SAW chemical composition and mechanical properties required for the weld deposit • thickness of base metal to be welded • joint accessibility • position in which the weld is to be made • frequency or volume of welding to be performed SAW methods Semiautomatic Mechanised Automatic
  • 309. Submerged Arc Welding 4/23/2007 340 of 691 - + Power supply Filler wire spool Flux hopper Wire electrode Flux Slide rail
  • 310. SAW process variables 4/23/2007 341 of 691 • welding current • current type and polarity • welding voltage • travel speed • electrode size • electrode extension • width and depth of the layer of flux
  • 311. SAW process variables 4/23/2007 342 of 691 Welding current •controls depth of penetration and the amount of base metal melted & dilution
  • 312. SAW operating variables 4/23/2007 343 of 691 Current type and polarity •Usually DCEP, deep penetration, better resistance to porosity •DCEN increase deposition rate but reduce penetration (surfacing) •AC used to avoid arc blow; can give unstable arc
  • 313. SAW Consumables (Covered in detail in Section 14) 4/23/2007 344 of 691 Fused fluxes advantages: •good chemical homogeneity •easy removal of fines without affecting flux composition •normally not hygroscopic & easy storage and handling •readily recycled without significant change in particle size or composition Fused fluxes disadvantages: •difficult to add deoxidizers and ferro-alloys (due to segregation or extremely high loss) •high temperatures needed to melt ingredients limit the range of flux compositions
  • 314. SAW Consumables 4/23/2007 345 of 691 Agglomerated fluxes advantages: • easy addition of deoxidizers and alloying elements • usable with thicker layer of flux when welding • colour identification Agglomerated fluxes disadvantages: • tendency to absorb moisture • possible gas evolution from the molten slag leading to porosity • possible change in flux composition due to segregation or removal of fine mesh particles
  • 315. SAW equipment 4/23/2007 346 of 691 Power sources can be: • transformers for AC • transformer-rectifiers for DC Static characteristic can be: • Constant Voltage (flat) - most of the power sources • Constant Current (drooping)
  • 316. SAW equipment 4/23/2007 347 of 691 Constant Voltage (Flat Characteristic) power sources: • most commonly used supplies for SAW • can be used for both semiautomatic and automatic welding • self-regulating arc • simple wire feed speed control • wire feed speed controls the current and power supply controls the voltage • applications for DC are limited to 1000A due to severe arc blow (also thin wires!)
  • 317. ARC CHARACTERISTICS 4/23/2007 348 of 691 Volts Amps OCV Constant Voltage Characteristic Small change in voltage = large change in amperage The self adjusting arc. Large arc gap Small arc gap
  • 318. SAW equipment 4/23/2007 349 of 691 Constant Current (Drooping Characteristic) power sources: • Over 1000A - very fast speed required - control of burn off rate and stick out length • can be used for both semiautomatic and automatic welding • not self-regulating arc • must be used with a voltage-sensing variable wire feed speed control • more expensive due to more complex wire feed speed control • arc voltage depends upon wire feed speed whilst the power source controls the current • cannot be used for high-speed welding of thin steel
  • 319. SAW equipment 4/23/2007 350 of 691 Welding heads can be mounted on a: Tractor type carriage • provides travel along straight or gently curved joints • can ride on tracks set up along the joint (with grooved wheels) or on the workpiece itself • can use guide wheels as tracking device • due to their portability, are used in field welding or where the piece cannot be moved Courtesy of ESAB AB Courtesy of ESAB AB
  • 320. SAW operating variables 4/23/2007 351 of 691 Welding current •too high current: excessive excess weld metal (waste of electrode), increase weld shrinkage and causes greater distortions •excessively high current: digging arc, undercut, burn through; also a high and narrow bead & solidification cracking •too low current: incomplete fusion or inadequate penetration •excessively low current: unstable arc
  • 321. SAW operating variables 4/23/2007 352 of 691 Welding voltage •welding voltage controls arc length •an increased voltage can increase pick-up of alloying elements from an alloy flux •increase in voltage produce a flatter and wider bead •increase in voltage increase flux consumption •increase in voltage tend to reduce porosity •an increased voltage may help bridging an excessive root gap
  • 322. SAW operating variables 4/23/2007 353 of 691 Welding voltage •low voltage produce a “stiffer” arc & improves penetration in a deep weld groove and resists arc blow •excessive low voltage produce a high narrow bead & difficult slag removal
  • 323. SAW operating variables 4/23/2007 354 of 691 Welding voltage •excessively high voltage produce a “hat-shaped” bead & tendency to crack •excessively high voltage increase undercut & make slag removal difficult in groove welds •excessively high voltage produce a concave fillet weld that is subject to cracking
  • 324. SAW operating variables 4/23/2007 355 of 691 Travel speed •increase in travel speed: decrease heat input & less filler metal applied per unit of length, less excess weld metal & weld bead becomes smaller
  • 325. SAW operating variables 4/23/2007 356 of 691 Travel speed •excessively high speed lead to undercut, arc blow and porosity •excessively low speed produce “hat-shaped” beads danger of cracking •excessively low speed produce rough beads and lead to slag inclusions
  • 326. SAW operating variables 4/23/2007 357 of 691 Electrode size •at the same current, small electrodes have higher current density & higher deposition rates
  • 327. SAW operating variables 4/23/2007 358 of 691 Electrode extension •increased electrode extension adds resistance in the welding circuit I increase in deposition rate, decrease in penetration and bead width •to keep a proper weld shape, when electrode extension is increased, voltage must also be increased •when burn-through is a problem (e.g. thin gauge), increase electrode extension •excessive electrode extension: it is more difficult to maintain the electrode tip in the correct position
  • 328. SAW operating variables 4/23/2007 359 of 691 Depth of flux •depth of flux layer influence the appearance of weld •usually, depth of flux is 25-30 mm •if flux layer is to deep the arc is too confined, result is a rough ropelike appearing weld •if flux layer is to deep the gases cannot escape & the surface of molten weld metal becomes irregularly distorted •if flux layer is too shallow, flashing and spattering will occur, give a poor appearance and porous weld
  • 329. SAW technological variables 4/23/2007 363 of 691 Travel angle effect - Butt weld on plates Penetration Deep Moderate Shallow Excess weld metal Maximum Moderate Minimum Tendency to undercut Severe Moderate Minimum
  • 330. SAW technological variables 4/23/2007 364 of 691 Earth position + - Direction of travel •welding towards earth produces backward arc blow •deep penetration •convex weld profile
  • 331. SAW technological variables 4/23/2007 365 of 691 Earth position + - Direction of travel •welding away earth produces forward arc blow •normal penetration depth •smooth, even weld profile