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Duplex welding

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Duplex Steels

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Duplex welding

  1. 1. Welding Duplex steelsWelding Duplex steels Project SNDC PHASE 1 OMANProject SNDC PHASE 1 OMAN Mr. AndersMr. Anders ThörnqvistThörnqvist M. Sc MetM. Sc Met EngrEngr, IWE, IWI, IWE, IWI--EE Introduction 1
  2. 2. What is Duplex StainlessWhat is Duplex Stainless Steel?Steel? LowLow--carbon stainless steelscarbon stainless steels containing approx. equal parts ofcontaining approx. equal parts of ferrite and austeniteferrite and austenite from a balance of ferrite formersfrom a balance of ferrite formers (Cr,Mo) with austenite formers(Cr,Mo) with austenite formers (Ni,N) and heat treatment(Ni,N) and heat treatment Introduction 2
  3. 3. What is Duplex StainlessWhat is Duplex Stainless steelssteels ‡‡ Duplex (DSS) steels are as previousDuplex (DSS) steels are as previous mentioned a combination of ³ Carbon´mentioned a combination of ³ Carbon´ steels and ³Stainless´ steel.steels and ³Stainless´ steel. ‡‡ DSS microstructure is approximatelyDSS microstructure is approximately equal parts of Ferrite and Austenite.equal parts of Ferrite and Austenite. ‡‡ Duplex alloys exhibit someDuplex alloys exhibit some characteristics from bothcharacteristics from both FerriticFerritic andand Austenitic steels.Austenitic steels. ‡‡ ff Introduction 3
  4. 4. What is Duplex stainlessWhat is Duplex stainless steels?steels? ‡‡ As a result of this combination ofAs a result of this combination of structures (steels) the welding procedurestructures (steels) the welding procedure of Duplex steels require differentof Duplex steels require different parameters thanparameters than FerriticFerritic and Austeniticand Austenitic steels.steels. ‡‡ Attractive features off DSS steels are (asAttractive features off DSS steels are (as mentioned before, double Yield strengthmentioned before, double Yield strength ,while maintaining ductility and toughness,while maintaining ductility and toughness in comparison of Austenitic steelsin comparison of Austenitic steels Introduction 4
  5. 5. Introduction 5
  6. 6. Duplex Stainless SteelDuplex Stainless Steel Base Metal Upper Right, Weld Metal Bottom Left Source: The ESAB Group Introduction 6
  7. 7. Duplex SSDuplex SS ±± alloy 2205alloy 2205 ‡‡ Typically: 22 Cr, 5 Ni, 3 Mo, O.15 NTypically: 22 Cr, 5 Ni, 3 Mo, O.15 N ‡‡ Structure is austenite islands inStructure is austenite islands in ferriticferritic matrix ~ 50/50 is idealmatrix ~ 50/50 is ideal ‡‡ Benefits in DSS from:Benefits in DSS from: BCC 50%= Ferrite ,Body centered cubicBCC 50%= Ferrite ,Body centered cubic FCC 50% = Austenite, Face centeredFCC 50% = Austenite, Face centered cubiccubic Introduction 7
  8. 8. Duplex SSDuplex SS ±± (cont.)(cont.) ‡‡ Stress corrosion cracking resistanceStress corrosion cracking resistance substantially better than 304/316substantially better than 304/316 ‡‡ Pitting & crevice cor. Resistance equalPitting & crevice cor. Resistance equal or better than 316 in many mediaor better than 316 in many media ‡‡ Good resistance to erosion & abrasionGood resistance to erosion & abrasion Introduction 8
  9. 9. DSS WeldingDSS Welding -- GeneralGeneral RequirementsRequirements ‡‡ No preheatNo preheat ±± 300F/ 150 C degrees inter300F/ 150 C degrees inter--passpass temperature typicaltemperature typical ‡‡ Heat input 15 to 65 kJ/inHeat input 15 to 65 kJ/in-- 0.5 Kj0.5 Kj--2.52.5 KjKj mm.mm. ‡‡ To avoid high ferrite in welds, filler metalsTo avoid high ferrite in welds, filler metals with higher nickel used ~ 2209 with 9%with higher nickel used ~ 2209 with 9% nickel( to high content of ferrite, reducesnickel( to high content of ferrite, reduces toughness and ductility)toughness and ductility) ‡‡ Avoidance of arc strikes, oxidation, grindingAvoidance of arc strikes, oxidation, grinding out of cratersout of craters Introduction 9
  10. 10. Welding Processes UsedWelding Processes Used ‡‡ GTAW or TIGGTAW or TIG -- manualmanual -- orbital tube welding or automatic sheetorbital tube welding or automatic sheet ‡‡ SAWSAW--Submerged..Submerged.. ‡‡ GMAWGMAW ±± MIGMIG ‡‡ SMAW or covered electrodeSMAW or covered electrode Introduction 10
  11. 11. Duplex SSDuplex SS -- WeldingWelding ‡‡ Q = Heat input is calculated by followingQ = Heat input is calculated by following formula: U * I / V (mm/sec)formula: U * I / V (mm/sec) U = VoltageU = Voltage I = AmperageI = Amperage V= Speed, travel speed of welding, mmV= Speed, travel speed of welding, mm /sec/sec Introduction 11
  12. 12. Duplex WeldingDuplex Welding ‡‡ Good results in DSS digester construction do not come by chance, but by adhering to aGood results in DSS digester construction do not come by chance, but by adhering to a good quality assurance program.good quality assurance program. ‡‡ Poor practices that are forgiven with carbon steel or austenitic stainless steel fabrication canPoor practices that are forgiven with carbon steel or austenitic stainless steel fabrication can result in costly degradation of the superior physical and mechanical properties of DSS.result in costly degradation of the superior physical and mechanical properties of DSS. ‡‡ While ASME Code requirements cover a certain level of quality, additional measures areWhile ASME Code requirements cover a certain level of quality, additional measures are warranted for DSS construction.warranted for DSS construction. ‡‡ Examples are the qualification of mill product materials and welding procedures to ASTM ,Examples are the qualification of mill product materials and welding procedures to ASTM , and the followand the follow--up testing of shopup testing of shop-- and fieldand field--production weld coupons.production weld coupons. ‡‡ Routine monitoring of welding heat input andRoutine monitoring of welding heat input and interpassinterpass temperatures should also betemperatures should also be performed.performed. ‡‡ Ferrite balance of welds can be made using a portable meter such as aFerrite balance of welds can be made using a portable meter such as a FeritscopeFeritscope Production jointProduction joint fitupfitup and intermediate steps in the welding process should be verified andand intermediate steps in the welding process should be verified and documented by quality control.documented by quality control. ‡‡ The mill product material quality should be similarly monitored. Mills should give attention toThe mill product material quality should be similarly monitored. Mills should give attention to material surface finish and postmaterial surface finish and post--fabrication cleaning. Additional information on specificationsfabrication cleaning. Additional information on specifications and testing of DSS is often required.and testing of DSS is often required. Introduction 12
  13. 13. Calculation QCalculation Q--exampleexample ‡‡ Let¶s say (simplified) that we areLet¶s say (simplified) that we are measuring ³critical data´ from a weldingmeasuring ³critical data´ from a welding sequence. Data such as Voltage,sequence. Data such as Voltage, Amperage, traveling speed.Amperage, traveling speed. ‡‡ Voltage , was measured to 10V,Voltage , was measured to 10V, amperage 82, travel speed 0.7 mm /amperage 82, travel speed 0.7 mm / sec.sec. ‡‡ Q= 10*82 / 0.7 = 1.17Q= 10*82 / 0.7 = 1.17 kjkj/mm/mm Introduction 13
  14. 14. GTAW ProcessGTAW Process -- DSSDSS ‡‡ Used for root passes and orbital weldsUsed for root passes and orbital welds ‡‡ Filler essential for ferriteFiller essential for ferrite--austeniteaustenite balancebalance ‡‡ Ar + 20Ar + 20--40% He + up to 2.5% N40% He + up to 2.5% N22 toto counter N loss from weldcounter N loss from weld -- no hydrogenno hydrogen ‡‡ Backing gas to maintain weld N contentBacking gas to maintain weld N content Introduction 14
  15. 15. Manual vs Automatic OrbitalManual vs Automatic Orbital Tube WeldingTube Welding ‡‡ Short projects may favor manualShort projects may favor manual weldingwelding ‡‡ Manual welders better able toManual welders better able to accommodate poorer fitaccommodate poorer fit--up conditionsup conditions ‡‡ Orbital welds have more consistent rootOrbital welds have more consistent root weld beads and practically free fromweld beads and practically free from heat tintheat tint Introduction 15
  16. 16. Heat Tint? What is it?Heat Tint? What is it? Introduction 16
  17. 17. The Sample Numbers refer to the amount of oxygen in the purgingThe Sample Numbers refer to the amount of oxygen in the purging gas:gas: No.1No.1-- 10ppm10ppm No.2No.2 -- 25ppm25ppm No.3No.3 -- 50ppm50ppm No.4No.4 -- 100ppm100ppm No.5No.5 -- 200ppm No.6200ppm No.6 -- 500ppm No. 7500ppm No. 7 -- 1000ppm No.81000ppm No.8 -- 5000ppm5000ppm No.9No.9 --12500ppm No.1012500ppm No.10 --. 25000ppm. 25000ppm Note: welds on type 304L SS showed no significant difference inNote: welds on type 304L SS showed no significant difference in heatheat tint colour from type 316L.tint colour from type 316L. AWS D18.2 (1999):AWS D18.2 (1999): Heat Tint Levels on the Inside ofHeat Tint Levels on the Inside of Welded 316L Austenitic Stainless Steel TubeWelded 316L Austenitic Stainless Steel Tube Introduction 17
  18. 18. Heat TintHeat Tint -- Acceptance LimitsAcceptance Limits ‡‡ Acceptable limits could vary with endAcceptable limits could vary with end application service, D18.1 or D18.2application service, D18.1 or D18.2 ‡‡ Typically # 5, 200Typically # 5, 200 ppmppm and greater isand greater is unacceptableunacceptable ‡‡ An acceptance level should be identifiedAn acceptance level should be identified by number rather thanby number rather than ppmppm of oxygen orof oxygen or by workmanship standards for particularby workmanship standards for particular contractcontract Introduction 18
  19. 19. Factors Influencing Heat TintFactors Influencing Heat Tint ‡‡ Oxygen in backing gas increases HTOxygen in backing gas increases HT ‡‡ Moisture in backing gas increases HTMoisture in backing gas increases HT ‡‡ Contaminants such as hydrocarbonsContaminants such as hydrocarbons increase discolorationincrease discoloration ‡‡ Hydrogen in backing gas decreases HTHydrogen in backing gas decreases HT ‡‡ Metal surface finish can affectMetal surface finish can affect appearanceappearance Introduction 19
  20. 20. Formation of Sigma phase &Formation of Sigma phase & Alpha phaseAlpha phase Introduction 20
  21. 21. Sigma phase & Alpha phaseSigma phase & Alpha phase ‡‡ What is this??What is this?? ‡‡ Sigma phase, an interSigma phase, an inter--metallic phasemetallic phase that occurs in DSS steels and reducesthat occurs in DSS steels and reduces both Corrosion protection and lower theboth Corrosion protection and lower the toughness of the steel.toughness of the steel. ‡‡ Sigma phase forms in the temperatureSigma phase forms in the temperature range of 700 Crange of 700 C ±± 980 C.980 C. Introduction 21
  22. 22. How to avoid Sigma Phase?How to avoid Sigma Phase? ‡‡ Simplified we can say that the control ofSimplified we can say that the control of heat input (Q), will help us to reduce theheat input (Q), will help us to reduce the formation of this Phase.formation of this Phase. ‡‡ Heat input (Q) is in this case controlledHeat input (Q) is in this case controlled by the way we weld this material.by the way we weld this material. ‡‡ It is most important to follow allIt is most important to follow all instructions regarding heat input andinstructions regarding heat input and interinter--pass temperature.pass temperature. ‡‡ We will discuss this issue further, later on in the Education, control of Heat inputWe will discuss this issue further, later on in the Education, control of Heat input--WPSWPS Introduction 22
  23. 23. Alpha PrimeAlpha Prime ‡‡ Alpha prime is anAlpha prime is an embrittlingembrittling phase thatphase that also occurs in thealso occurs in the FerriticFerritic, BBC phase of, BBC phase of Duplex steels.Duplex steels. ‡‡ EmbrittilingEmbrittiling occurs in the temperatureoccurs in the temperature range 475 C, and the time to form thisrange 475 C, and the time to form this phase various from minutes to hours.phase various from minutes to hours. ‡‡ In order to avoid this phase, same asIn order to avoid this phase, same as the Sigma phase we need to control Q,the Sigma phase we need to control Q, heat inputheat input.. Introduction 23
  24. 24. Welding QualificationsWelding Qualifications ‡‡ PQRPQR--Procedure Qualification recordProcedure Qualification record ‡‡ Welding Procedure SpecificationWelding Procedure Specification (WPS)(WPS) -- for each type of weldfor each type of weld ‡‡ Performance QualificationPerformance Qualification -- to testto test welder¶s abilitywelder¶s ability ‡‡ Preconstruction Weld Samples (PWS)Preconstruction Weld Samples (PWS) -- 3 welds made by each welder to aid3 welds made by each welder to aid in evaluating production weldsin evaluating production welds Introduction 24
  25. 25. DSS Welding & PreparationDSS Welding & Preparation General:General: Welders that have experience ofWelders that have experience of welding Austenitic stainless steelswelding Austenitic stainless steels should be able to apply their skills andshould be able to apply their skills and technique acquired with these alloys totechnique acquired with these alloys to DSS steels welding.DSS steels welding. Introduction 25
  26. 26. DSS Welding & PreparationDSS Welding & Preparation General:General: The welding characteristics, puddleThe welding characteristics, puddle manipulation, and viscosity of the twomanipulation, and viscosity of the two families of alloys (Ferrite and Austenite)families of alloys (Ferrite and Austenite) are similar; however the puddle, controlare similar; however the puddle, control of melt in DSS is more viscose's thanof melt in DSS is more viscose's than Austenitic steels and therefore moreAustenitic steels and therefore more difficult to weld by hand.difficult to weld by hand. Introduction 26
  27. 27. Cleaning before WeldingCleaning before Welding ‡‡ The weld area to be cleaned before welding includesThe weld area to be cleaned before welding includes the joint edges and about 40 mm beside the actualthe joint edges and about 40 mm beside the actual weld area, closest to weld area. i.e. on each side,weld area, closest to weld area. i.e. on each side, insideinside-- outside pipe.outside pipe. Introduction 27
  28. 28. Cleaning before WeldingCleaning before Welding ‡‡ Improper cleaning can cause weld defects such asImproper cleaning can cause weld defects such as cracks, porosity and lack of fusion.cracks, porosity and lack of fusion. ‡‡ The joint should be free of surface oxides such asThe joint should be free of surface oxides such as might be left after thermal cutting.might be left after thermal cutting. ‡‡ Grinding, brushing or other mechanical means shouldGrinding, brushing or other mechanical means should be used in order to remove all paint, scales,be used in order to remove all paint, scales, oxidoxid andand dirt.dirt. ‡‡ Oil and grease compounds can be removed byOil and grease compounds can be removed by suitable solvent cleaning, followed by a thoroughsuitable solvent cleaning, followed by a thorough rinse.rinse. Introduction 28
  29. 29. Cleaning before WeldingCleaning before Welding ‡‡ There is a number of elements andThere is a number of elements and compounds that can cause cracking,compounds that can cause cracking, reduce corrosion protection if notreduce corrosion protection if not removed!removed! Introduction 29
  30. 30. Cleaning before welding &Cleaning before welding & toolstools ‡‡ Hand tools, such as wire brushed, used in fabricationHand tools, such as wire brushed, used in fabrication of duplex steels should by all means be made fromof duplex steels should by all means be made from stainless steel,stainless steel, and should be used exclusively onand should be used exclusively on duplex steels materialduplex steels material.. ‡‡ Grinding wheels etc, same procedure apply in thisGrinding wheels etc, same procedure apply in this section, only grinding wheels suitable for grinding SSsection, only grinding wheels suitable for grinding SS should be used to grind DSS.should be used to grind DSS. ‡‡ A good way to avoided confusion , mix up withA good way to avoided confusion , mix up with material etc, is to use a coloring system.material etc, is to use a coloring system. Introduction 30
  31. 31. Cleaning before welding &Cleaning before welding & toolstools ‡‡ A very practical way to avoid mix up betweenA very practical way to avoid mix up between material is just to use this coloration system.material is just to use this coloration system. ‡‡ For example we can by a proper procedure designateFor example we can by a proper procedure designate thethe color green to be marked on all material used incolor green to be marked on all material used in combination with DSS handling and welding.combination with DSS handling and welding. Everything from consumables to brushes.Everything from consumables to brushes. ‡‡ The actual marking is mostly done by the use ofThe actual marking is mostly done by the use of spray paint and applied ³directly´ to the object inspray paint and applied ³directly´ to the object in questionquestion.. Introduction 31
  32. 32. DSSDSS--JointsJoints--Fit upFit up ‡‡ In respect to welding duplex steels, a weld jointIn respect to welding duplex steels, a weld joint design must facilitate full penetration.design must facilitate full penetration. ‡‡ The best way to prepare a bevel, weld edgeThe best way to prepare a bevel, weld edge preparation is to use machining rather then grindingpreparation is to use machining rather then grinding ‡‡ When grinding must be used, special attention shouldWhen grinding must be used, special attention should be given to the uniformity of the weld preparation andbe given to the uniformity of the weld preparation and the fitthe fit--up in order to provide uniformity of the landup in order to provide uniformity of the land thickness or gap.thickness or gap. ‡‡ Any grinding burr should be removed to maintainAny grinding burr should be removed to maintain complete fusion and penetrationcomplete fusion and penetration Introduction 32
  33. 33. DSSDSS--JointsJoints--Fit upFit up Introduction 33
  34. 34. What is an WPS?What is an WPS? ‡‡ A WPS is a document that describes how welding is to be carried out inA WPS is a document that describes how welding is to be carried out in production.production. They are recommended for all welding operations and manyThey are recommended for all welding operations and many application codes and standards make them mandatoryapplication codes and standards make them mandatory ‡‡ What information should they include?What information should they include? ‡‡ Sufficient details to enable any competent person to apply the information andSufficient details to enable any competent person to apply the information and produce a weld of acceptable quality.produce a weld of acceptable quality. The amount of detail and level of controlsThe amount of detail and level of controls specified on a WPS is dependant on the application and criticality of the joint tospecified on a WPS is dependant on the application and criticality of the joint to be welded.be welded. ‡‡ For most applications the information required is generally similar to thatFor most applications the information required is generally similar to that recorded on a Procedure Qualification Record (PQR) or Welding Procedurerecorded on a Procedure Qualification Record (PQR) or Welding Procedure Approval Record (WPAR), except that ranges are usually permitted onApproval Record (WPAR), except that ranges are usually permitted on thicknesses, diameters, welding current, materials, joint types etc.thicknesses, diameters, welding current, materials, joint types etc. ‡‡ If a WPS is used in conjunction with approved welding procedures then theIf a WPS is used in conjunction with approved welding procedures then the ranges stated should be in accordance with the approval ranges permitted byranges stated should be in accordance with the approval ranges permitted by the welding procedure.the welding procedure. Introduction 34
  35. 35. What is a WPS?What is a WPS? ‡‡ However careful consideration should be given to the ranges specified toHowever careful consideration should be given to the ranges specified to ensure they are achievable, as the ranges given by welding procedureensure they are achievable, as the ranges given by welding procedure standards do not always represent good welding practice.standards do not always represent good welding practice. For example weldingFor example welding positions permitted by the welding procedure standard may not be achievable orpositions permitted by the welding procedure standard may not be achievable or practical for certain welding processes or consumables.practical for certain welding processes or consumables. ‡‡ EN ISO 15609EN ISO 15609--1 (formally EN 288 Part 2)1 (formally EN 288 Part 2) European Standard For WeldingEuropean Standard For Welding Procedure SpecificationsProcedure Specifications EN ISO 15609 Defines the contents of a Welding Procedure Specification in theEN ISO 15609 Defines the contents of a Welding Procedure Specification in the form of a list of information that should be recorded.form of a list of information that should be recorded. For some applications itFor some applications it may be necessary to supplement or reduce the list. For example only in themay be necessary to supplement or reduce the list. For example only in the case of a procedure requiring heat input control would there be a necessity tocase of a procedure requiring heat input control would there be a necessity to quote travel speed or runquote travel speed or run--out length for manual processes.out length for manual processes. ‡‡ ASME IXASME IX American Boiler and Pressure Vessel CodeAmerican Boiler and Pressure Vessel Code QW 250 Lists the variables for each welding process, all the variables statedQW 250 Lists the variables for each welding process, all the variables stated should be addressed.should be addressed. The range permitted by the WPS is dictated by the PQRThe range permitted by the WPS is dictated by the PQR or PQR¶s used to qualify it.or PQR¶s used to qualify it. Introduction 35
  36. 36. What is a WPS?What is a WPS? ‡‡ Typical Items That Should Be Recorded On W.P.S:Typical Items That Should Be Recorded On W.P.S:-- Common to all ProcessesCommon to all Processes .. ‡‡ Procedure numberProcedure number ‡‡ Process typeProcess type ‡‡ Consumable Size, Type and full Codification.Consumable Size, Type and full Codification. ‡‡ Consumable Baking Requirement if applicableConsumable Baking Requirement if applicable ‡‡ Parent material grade and spec.Parent material grade and spec. ‡‡ Thickness range.Thickness range. ‡‡ Plate or Pipe, Diameter rangePlate or Pipe, Diameter range ‡‡ Welding PositionWelding Position ‡‡ Joint Fit Up, Preparation, Cleaning, Dimensions etc.Joint Fit Up, Preparation, Cleaning, Dimensions etc. ‡‡ Backing Strip, Back Gouging information.Backing Strip, Back Gouging information. ‡‡ PrePre--Heat (Min Temp and Method)Heat (Min Temp and Method) ‡‡ InterpassInterpass If Required (Maximum Temperature recorded )If Required (Maximum Temperature recorded ) ‡‡ Post Weld Heat Treatment. If Required (Time and Temp)Post Weld Heat Treatment. If Required (Time and Temp) ‡‡ Welding Technique (Welding Technique (weaving,maxweaving,max run width etc.)run width etc.) ‡‡ Arc Energy Limits should be stated if impact tests are required or if the material being welded isArc Energy Limits should be stated if impact tests are required or if the material being welded is sensitive to heat inputsensitive to heat input Introduction 36
  37. 37. What is a PQR?What is a PQR? ‡‡ PQR's are not required if Standard Welding Procedures are used, see below for details. ThisPQR's are not required if Standard Welding Procedures are used, see below for details. This document contains details of the welding test, it must include details of all the parametersdocument contains details of the welding test, it must include details of all the parameters listed as variables in tables QW250 to QW265 for each process involved and all thelisted as variables in tables QW250 to QW265 for each process involved and all the destructive test results.destructive test results. ‡‡ The relevant variables for each type of welding process are clearly defined in tables QW250The relevant variables for each type of welding process are clearly defined in tables QW250 to QW265. The left hand column of each table defines the section and paragraph whereto QW265. The left hand column of each table defines the section and paragraph where each variable and its application to the table is explained in the code.each variable and its application to the table is explained in the code. ‡‡ Welding VariablesWelding Variables ‡‡ Variables used in a welding procedure test are divided into 3 categories :Variables used in a welding procedure test are divided into 3 categories :-- ‡‡ Essential VariablesEssential Variables Are variables that have a significant affect on the mechanicalAre variables that have a significant affect on the mechanical properties of a joint. They must not be changed except within the limits specified by thisproperties of a joint. They must not be changed except within the limits specified by this code. e.g. Material thickness range, Material Group etc.code. e.g. Material thickness range, Material Group etc. ‡‡ NonNon--Essential VariablesEssential Variables Are variables that have no significant affect on mechanicalAre variables that have no significant affect on mechanical properties. They can be changed without re qualification of the PQR.properties. They can be changed without re qualification of the PQR. ‡‡ Supplementary VariablesSupplementary Variables Are variables that have an affect on the impact properties of aAre variables that have an affect on the impact properties of a joint. They are classed as Nonjoint. They are classed as Non--Essential if impact testing is not requiredEssential if impact testing is not required ‡‡ All variables listed as essential, nonAll variables listed as essential, non--essential or supplementary should be addressed onessential or supplementary should be addressed on both the WPS and the PQR. If any of the variables do not apply to the particular applicationboth the WPS and the PQR. If any of the variables do not apply to the particular application then they should be specified as not applicable.then they should be specified as not applicable.Introduction 37
  38. 38. What is a PQR?What is a PQR?‡‡ Joint ConfigurationJoint Configuration Either plate or pipe can be used for the test piece (plate approves pipe and vice versa ref. QW211), anyEither plate or pipe can be used for the test piece (plate approves pipe and vice versa ref. QW211), any welding position approves all positions providing no impact tests are required ref. tables QW250 to QW265welding position approves all positions providing no impact tests are required ref. tables QW250 to QW265 and any joint geometry approves all geometry's, e.g. single V, double V, U prep, backed orand any joint geometry approves all geometry's, e.g. single V, double V, U prep, backed or unbackedunbacked.. ‡‡ A butt or groove weld approves branch and fillet welds but not the converse, ref. QW202. Non pressureA butt or groove weld approves branch and fillet welds but not the converse, ref. QW202. Non pressure retaining fillet welds in pipe or plate can be tested but they must be double sided if plate and at least theretaining fillet welds in pipe or plate can be tested but they must be double sided if plate and at least the dimensions illustrated in QW462.4a, ref. QW202.2c. Pressure retaining branch welds must be qualified bydimensions illustrated in QW462.4a, ref. QW202.2c. Pressure retaining branch welds must be qualified by groove (butt) welds.groove (butt) welds. ‡‡ Material GroupingMaterial Grouping Materials are assigned P numbers in QW420; a test in one P number approves all materials listed underMaterials are assigned P numbers in QW420; a test in one P number approves all materials listed under that P number, except where impact tests are required then approval is restricted to materials listed in thethat P number, except where impact tests are required then approval is restricted to materials listed in the group number within the P number. Other P number groupings are permissible ref. QW424.1 for details.group number within the P number. Other P number groupings are permissible ref. QW424.1 for details. Ref QW 424.1 for further details.Ref QW 424.1 for further details. ‡‡ It is normally permissible if the material is not listed in QW422 to assign it to a P number which listsIt is normally permissible if the material is not listed in QW422 to assign it to a P number which lists materials with the same metallurgical and mechanical properties although this is not in strict conformancematerials with the same metallurgical and mechanical properties although this is not in strict conformance with the code. Typically BS1501 151 430A low carbon steel could be regarded as P1 and stainless steelswith the code. Typically BS1501 151 430A low carbon steel could be regarded as P1 and stainless steels such as 316, 304 as P8.such as 316, 304 as P8. ‡‡ Note P5, 9 & 10 are divided into sub groupsNote P5, 9 & 10 are divided into sub groups egeg 5A,5B etc., Treat each sub group like a separate P Number5A,5B etc., Treat each sub group like a separate P Number ‡‡ Dissimilar materials are acceptable providing they are compatible. For example P1 to P8, but this does notDissimilar materials are acceptable providing they are compatible. For example P1 to P8, but this does not cover P1 to P1 or P8 to P8.cover P1 to P1 or P8 to P8. ‡‡ Note S numbers are forNote S numbers are for pipeworkpipework to B31, a P number covers an S number but not the converseto B31, a P number covers an S number but not the converse Introduction 38
  39. 39. What is a PQR?What is a PQR? ‡‡ ConsumablesConsumables The ASME code uses its own specifications for consumablesThe ASME code uses its own specifications for consumables SFA.SFA. which is almost identical to the AWSwhich is almost identical to the AWS specification.specification. ‡‡ NOTE A change in consumable is only permissible providing it has the same F number and ANOTE A change in consumable is only permissible providing it has the same F number and A number (if applicable) as the P.Q.R..number (if applicable) as the P.Q.R.. ‡‡ Thickness LimitsThickness Limits Thickness limits Groove welds. See QW451 for precise details.Thickness limits Groove welds. See QW451 for precise details. ‡‡ When Impact tests are required the minimum thickness approved is restricted.When Impact tests are required the minimum thickness approved is restricted. See QW403.6See QW403.6 ‡‡ More than one PQR may be required to qualify dissimilar thicknessMore than one PQR may be required to qualify dissimilar thickness ‡‡ The thickness littleThe thickness little 't''t' of deposited weld metal for each process involved is approved from 0 to 2xt except:of deposited weld metal for each process involved is approved from 0 to 2xt except:-- MIG/MAG (GMAW/FCAW) dip transfer weld of deposited thickness less than ½" approves maximumMIG/MAG (GMAW/FCAW) dip transfer weld of deposited thickness less than ½" approves maximum thickness of 1.1 x t only Ref: QW255 (QW403.10)thickness of 1.1 x t only Ref: QW255 (QW403.10) ‡‡ If any Pass in a single orIf any Pass in a single or multipassmultipass weld > ½" then the thickness approval equalsweld > ½" then the thickness approval equals 1.1xT1.1xT ‡‡ Dissimilar Thickness QW202.4:Dissimilar Thickness QW202.4:-- The thicker and thinner part must be qualified, Except P8 and P4X theThe thicker and thinner part must be qualified, Except P8 and P4X the thinner part can be qualified if no Impacts and test coupon > 6mm thick.thinner part can be qualified if no Impacts and test coupon > 6mm thick. ‡‡ Thickness limits for fillet welds as per QW462.4a or QW462.4d qualify all fillet weld sizes on all baseThickness limits for fillet welds as per QW462.4a or QW462.4d qualify all fillet weld sizes on all base material thicknesses and all diameters in one testmaterial thicknesses and all diameters in one test Introduction 39
  40. 40. What is a PQR?What is a PQR? ‡‡ Testing Requirements (Ref QW 463 for location of specimens)Testing Requirements (Ref QW 463 for location of specimens) ‡‡ Unlike EN288 there is no requirement for any nonUnlike EN288 there is no requirement for any non--destructive testing such as radiography or MPI/DPI,destructive testing such as radiography or MPI/DPI, although I would recommend radiography for butt welds.although I would recommend radiography for butt welds. ‡‡ The testing requirement for groove welds are as follows:The testing requirement for groove welds are as follows:-- ‡‡ Two Transverse tensile tests (QW150).Two Transverse tensile tests (QW150). ‡‡ Two Root bends and Two face bends unless the plate thickness exceeds 3/8" then 4 side bends areTwo Root bends and Two face bends unless the plate thickness exceeds 3/8" then 4 side bends are required. All bend tests should be done to QW160 using the correct former ref. QW466 to an angle of 180required. All bend tests should be done to QW160 using the correct former ref. QW466 to an angle of 180 degrees. Longitudinal (all weld) bend tests are not recommended unless the base/weld materials differdegrees. Longitudinal (all weld) bend tests are not recommended unless the base/weld materials differ markedly in bending properties.markedly in bending properties. See QW 466 for exceptions and precise details.See QW 466 for exceptions and precise details. ‡‡ The testing requirement for fillet welds on plate is 5 macro sections only, for Pipe fillet welds 4 macroThe testing requirement for fillet welds on plate is 5 macro sections only, for Pipe fillet welds 4 macro sections. No fracture test requiredsections. No fracture test required Introduction 40
  41. 41. DiscontinuitesDiscontinuites-- Weld defectsWeld defects We will discuss common weldingWe will discuss common welding defects and cause, not only relateddefects and cause, not only related to DSSto DSS Hot Cracks Cold Cracks PORES Lack of Fusion Undercut Misalignment Arc strikes Material Defects Oxide inclusions Pipe/Crater cracks
  42. 42. Hot CracksHot Cracks
  43. 43. Hot Cracks or Solidification cracksHot Cracks or Solidification cracks ‡‡ Formed under high temperatures, 1200Formed under high temperatures, 1200°°CC ‡‡ «under influence of shrinkage and tensions.«under influence of shrinkage and tensions. ‡‡ Crack is always formed in the middle if weldCrack is always formed in the middle if weld ‡‡ Fillet weld is most sensitive for Cold CracksFillet weld is most sensitive for Cold Cracks ‡‡ Can hide benith the surface.Can hide benith the surface.
  44. 44. Why Hot Cracks??Why Hot Cracks?? ‡‡ High content of Carbon, sulfur, niob and phosforHigh content of Carbon, sulfur, niob and phosfor ‡‡ Most sensitive in Root area and tack welding.Most sensitive in Root area and tack welding. ‡‡ Welds geometry is also an important faktorWelds geometry is also an important faktor ‡‡ UCS: Units of crack susceptibilityUCS: Units of crack susceptibility ‡‡ UCS: 230C+190S+75P+45NbUCS: 230C+190S+75P+45Nb--12,3Si12,3Si--5,4Mn5,4Mn--11 ‡‡ UCS below or = 10 small riskUCS below or = 10 small risk ‡‡ UCS over 30 big riskUCS over 30 big risk
  45. 45. ContinueContinue ‡‡ Big gaps in between welding objects, increase theBig gaps in between welding objects, increase the risk of Hot cracks.risk of Hot cracks. ‡‡ Concave weld bead, increase riskConcave weld bead, increase risk
  46. 46. What to do??What to do?? ‡‡ Clean material.Clean material. ‡‡ Lower power supply, Heat Input.Lower power supply, Heat Input. ‡‡ Modify the groove.Modify the groove. ‡‡ Minimize gapMinimize gap ‡‡ Control the weld sequence.Control the weld sequence. ‡‡ Reduce the level mixture between baseReduce the level mixture between base material and filler material.material and filler material.

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