Defectos soldadura

1. Slide 4 of 81

4. COMMONLY OBSERVED DISCONTINUITIES
IN FUSION WELDING
TYPE EXISTS REMARKS
Lamination Pm Base metal, genarally near mid thickness of section.
Delamination Pm ,,
Seams & laps Pm Base metal surface, often at all times longitudinal.
Lamellar tears Pm Invariably near the HAZ in flange plate of T-butt joint.
Cracks Pm, Wm
Wm/Pm
Restraint, Hot, Brittle & Under bead cold cracks; which may be
either in longitudinal or transvers direction.
Crater cracks Wm Usually with multi axial cracks at the point of termination.
Fissures Wm Micro cracks generally in fully austenitic stainless steel & less
ductile metal.
Stray flash Pm Appears away from the weld seam as a trail of arc spots with
micro fissures, excesively brittle & hard character.
Spatters Pm Globular weld particles ejected out of an arc zone & scattered
shabbily around over the base metal.
Pm = Parent metal; Wm = Weld metal; Pm/Wm = Junction of weld & base metal
Continued...

5. Weld decay &
stress corros-
ion cracks
Pm Precipitation of chromium carbide in austenitic stainless steels &
severely degrading the corrosion resistance property in HAZ; which
may also be associated with the stress corrosion cracks.
Oxidation Wm Inadequacy in gas shield or gas purge from the root side causes a
heavy black scale or an extremely rough crinkled appearance.
Craters Wm An unfilled concave crater causes a point of stress raiser.
Underfill Wm Inadequate weld metal filling and causing weakness.
Undercut Wm/Pm Groove made by the arc force & left unfilled, causes severe stress
concentration.
Overlap Wm/Pm Accumulation of weld, without fusion, causes an extremely voilent
point of sstress raiser.
Lack of fusion Wm,
Wm/Pm
Lack of union between the two weld beads or weld & base metal
causes stress concentration.
Lack of
penetration
Pm Inadequacy of through thickness fusion depth.
Solid particle
inclusion
Wm Trapped slag particle, tungsten or oxide (Al2O3) in weld.
Gas inclusion Wm Gas voids contained within the weld causes: Blow hole, Gas pore,
Piping, Worm holes, Linear, Clustered or Scattered porasity.
Pm = Parent metal; Wm = Weld metal; Pm/Wm = Junction of weld & base metal

6. - due to segregation

9. Lamellar Tearing:

10. • Dilution
• Heat input

11. The dilution:
Fm
Pm
Wm
Wm = Fm + Pm
Dilution% = Pm / Wm X 100
Pm = Melted Parent metal
Fm = Melted Filler metal
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12. The heat input:
Kj / mm = I.V./ S.1000
I = Current across the arc.
V = Voltage across the arc.
S = The rate of arc motion mm/Sec.
‘‘Too low or high heat input both may equally be
proved detrimental.’’
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14. Solidification cracks due to the bead factor:
W = Bead Width
P = Bead Depth
W
P P
W
W/P>1 W/P<1
That is W/P

18. Cracks is detected in a radiograph, only when it produces a
change in thickness that is parallel to the x-ray beam. It appears
often zig-jagged with faint irregular line. Cracks can also appear
sometime as "tail" to an inclusion or porosity.

26. Carbon equivalent Recommended procedure
Lesser than 0.40% Any electrode may be used, no problem up to the
combined thickness of 50mm.
Greater than 0.40% Preheat 100 to 200 0C or switch over to the basic
electrode.
Up to 0.55% Preheat 200 to 350 0C or switch over to the basic
electrode with reduced temp.
Abov 0.55% Use only the basic electrode & also preheat 200 -
350 0C or switch over to stainless steel electrode
of high ferrite.
C eq% = C% +
Mn%
6
(Cr + Mo + V)%
5 15
(Cu+Ni)%
+ +

27. Preheat Temp. for C & C-Mn Steel only:
0F = 1,000 (C% - 0.11) + 18 t"
Where C% is only up to 0.65% max.
A Saiferian formula for preheat to prevent cold cracks;
0C = 350 [C]e - 0.25
[C]e= [C]c + [C]t
[C]c = C% + + +
(Mn + Cr)%
9
Ni%
18
7Mo%
90
[C]t = [C]c X 0.005 t
t = Thickness in mm

34. Undercut is an erosion of the base metal next to the toe of the weld
face. It appears in radiograph as a dark irregular line on outer edge
of the weld.

35. Root undercut is an erosion of the base metal next to the root of the
weld. It appears in radiographic images as a dark irregular line offset
from the centerline of the weldment. Undercutting is not as straight
edged as LOP because it does not follow the straight edge

36. Root concavity or suck back is a condition where the weld metal
has contracted as it cools down & has been drawn up into the root of
the weld. On a film it appears similar to the lack of root penetration
but the line has irregular wide edges and placed in the middle.

39. Cold lap is a condition where the weld metal does not fuse with the
base metal or the previous weld bead (interpass cold lap). The arc
does not melt the base metal and causes the molten puddle to flow
into the base metl without the proper bonding.

40. Incomplete fusion is a condition where the weld metal does not
fuse with the base metal. Appearance on radiograph is usually a
darker line or lines oriented in the direction of the weld seam along
the weld joining area.

42. Burn through (icicles) results when too much heat causes weld to
pierce through. Lumps of weld metal sag through the seam creating
a thick globular condition on the root face. On a radiograph, burn
through appears as dark spots surrounded by light globular areas.
Whiskers are the short lengths of electrode wire, visible on
the top or bottom surfaces of the weld or contained within the
weld. On radiograph they appear as light, "wire like" indications.

44. Lack of penetration occurs when the weld metal fails to penetrate
through the joint. Allows a linear stress riser like discontinuity from
which a crack may initiate. The appearance on a radiograph is a dark
well-defined straight edges that follows the land or root face down the
center of a joint.

46. •Gas pore _ singular.
•Blowhole _ singular.
•Scattered Porasity.
•Cluster Porasity.
•Linear Porasity.
•Piping.
• Worm holes.
Gas inclusion
Fine Severe

52. Porosity appears often as dark round irregular spots in clusters or
rows. Sometimes it is elongated and may have an appearance of a
tail. This is the result of gas attempting to escape while the metal is
still in a liquid state & is called wormhole porosity. All porosity is
indeed a void will have a darker density than the surrounding.

53. Cluster porosity is caused when electrodes are contaminated with
moisture or hydrocarbon. It appears like regular porosity in a film
but the indications will be grouped close together.

54. • Oxide inclusion/ Puckering

57. Slag inclusions are the nonmetallic solid materials trapped in weld
or between the weld and base metal. In a radiograph, dark, jagged
asymmetrical shapes within the weld or along the weld joint areas
are indicative of slag inclusions.

59. Tungsten inclusions. Tungsten is a brittle and dense material used
as an electrode in tungsten inert gas welding. If an incorrect welding
procedures & skill is performed, then only the tungsten gets trapped.
Radiographically, tungsten is more dense than aluminum or steel;
therefore, it shows as a lighter area with a distinct outline on the
radiograph

60. Oxide inclusions are usually visible on the surface of a weld mtal
(especially aluminum). Oxide inclusions are less dense than the surr -
ounding metals and, thus it appears as dark irregular shaped discon
-tinuity in radiograph. This is also referred as puckering in ISO.

63. The radiographic image is a noticeable difference in density between
the two mismatched pieces. The difference in density is caused by the
difference in material thickness. The dark, straight line is caused by
failure of the weld metal to fuse with the land area.

67. Excessive reinforcement is an area of a weld added in excess of
that specified by the drawings and codes. The appearance on a rad-
iograph is a localized & less darker area. A visual examination will
easily determine if the weld reinforcement is in excess.

72. Underfilling is an area where the deposited weld metal is less than
the required thickness. It is easy to determine by RT films, because
the image density in the area of inadequacy will be darker than the
surrounding image density.

73. Distortion
:
Distortion is an unavoidable phenom
-enon of fusion welding.
Type:
• Longitudinal distortion; &
• Transvers distortion.
• Angular distortion;

74. Distortion:

76. Remedy: only to minimise.
• Reduce the cause of shrinkage forces;
• Make use of the shrinkage forces; &
• Balance the shrinkage forces.

77. Reduce the cause of shrinkage forces:
1. Do not weld __ if possible.
2. Reduce the number of joints.
3. Improve the joint design & fit-up.
4. Avoid excessive root gap & mismatch.
5. Avoid over welding.
6. Reduce the number of runs.
7. Use larger size electrodes.
8. Use iron powder type electrode.
9. Use semi or fully mechanized welding.

78. RO
RF
GA
GA=Groove / Included angle
RF = Root face
RO = Root opening
 Fusion faces


© Shoulder
©
©
 Obviously the poor fit-up demands more metal to be
filled in and thus the more shrinkage / distortion.

79. t
W
W
Effective throat area gets reduced in proportion
to the root gap and an over welding by 1.6mm to
a 6 mm given fillet size, the cross section area
of weld increases by a margin of 56%.

80. Make use of shrinkage forces:

81. Balance the shrinkage forces:
Use an appropriate welding scequence.
i.e. Back step & intermittent welding techniques.
Use external force:
i.e. Tack weld, Jigs, Fixtures & Clamps.