Welding Defect .pdf

Welding Defect .pdf

1. Welding Defects
Any discontinuity (or irregularity) in the weld metal, which exceeds the applicable code limit, is
termed as aWELD DEFECT(or Welding Defect).Please note that a discontinuity can be called as a
defect only whenif it exceeds the specified code limit, hence we can say that every defect
present in the weld metal is a discontinuity but every discontinuity present in the weld metal
may not necessarily be a defect. A defect can be macroscopic or microscopic.
(Note: Discontinuity is also termed as “reflector”in some codes and texts)

2. Defects may occur due to the following reasons
1. Incorrect welding parameters
2. Inappropriate welding procedures
3. Poor process condition
4. Inappropriate selection of filler metal and parent metal
5. Unskilled welder or welding operator
6. Incorrect job preparations

3. Defects can be classified asexternal
defect(also known as visual defect or
surface defect) orinternal
defect(also known as hidden defect
or subsurface defect).External defects
are those which are found on the surface
itself. Internal defects are those which
exist in the material at some depth. We
can say that defects that are not present
on the surface are internal defects.Please
see the following table
Classification of Defects

4. ●1.CRACKS:
●Itisthemostdangerousofall
defects.Cracksmaybeofanysizeor
shape;itcanbeeithermicroscopicor
macroscopic.Cracksmayappear
anywherei.e.onthesurface,
subsurface,atanydepth,oratthe
root.Thecrackoccurswhenlocalized
stressexceedstheultimateTensile
Stress(UTS)ofthematerial.Itmay
propagatewithinthematerial.
Cracksareoftwotypes;
•Hot Cracks
•Cold Crack
Different types of welding defects along with their
causes

5. ●HOTCRACKS:
●Hotcracksoccurduringweldingorsoonafterthecompletionofwelding,Itis
mostlikelytooccurduringthesolidificationofthemoltenweldpool.Hot
cracksmostlyoccurintheweldmetalbutitmayoccurattheHeatAffected
Zone(HAZ)regiontoo.
●Whenahotcrackoccursontheweldmetal,thenitistermedasSolidification
CrackandifitoccursintheHAZthencalledLiquationcrack.
●Causes of Hot Crack:
1. High concentration of residual stress
2. Rapid cooling of the molten weld pool
3. High thickness of base material
4. Poor ductility of welded material
5. High welding current
6. Inadequate heat treatment
●Prevention:
1. Preheating and post-heating to avoid rapid cooling
2. Using right filler metal
HOTCRACKS:

6. ●Cold cracks occur after the solidification of weld metal; it can even develop
several days after completion of welding. Most of the time it develops in the
HAZ but may occur on the weld metal too. It is often associated with non-
metallic inclusion.
●Causes of Cold Crack:
●1.DiffusionofHydrogenatoms:Hydrogenatomscausecoldcracking.These
hydrogenatomsmaybeinducedintheweldmetalfromthesurrounding,
electrode,basemetal,oranycontaminationpresentontherootface.
●2.LackofPreheating:Duetoinadequatepreheating,microstructuralchanges
maytakeplace.Microstructuralcrystalsmayre-structureitselftoform
martensite.Martensiteisverypronetocracks.Preheatingalsohelpsin
reducingthediffusionofhydrogenatomsandensuresnomoistureonthe
jointbeforewelding.
●Prevention
●1.Preheatingand postweldingthe weld metal
2.UsinglowHydrogenelectrode
COLD CRACKS:

7. ●Star crack is a type of hot crackand it develops at the crater
on the weld metal. A crater is a depression formed on the
weld bead where the arc gets broken or when the electrode
is changed.
It develops when the center of the weld pool solidifies before
its surroundings and due to this the center pulls the outer
weld and thus star cracks are formed.
STAR CRACK (CRATER CRACK):

8. ●Porosity is a cavity-like discontinuity andoccurs due to the entrapment of
gases in the molten weld pool.These entrapped gases don’t get a chance to
escape from the molten weld pool and hence cause porosity or
blowholes.Porosity is basically a small pore or void, whereas,blowholes
are comparatively largerhole or cavity.
●Porosity may be present on the surface or inside the weld metal. Porosity
can occur individuallyor it may occur in groups also (mostly), group of
porosity is known ascluster porosity.
●Porosity is of five types mainly, these are;
1.Scattered Porosity
2.Cluster Porosity
3.Piping Porosity
4.Linear Porosity (Aligned Porosity)
5.Elongated Porosity
2. POROSITY & BLOW HOLES:

9. ●asesthat are entrappedand cause porosity are mostlyHydrogen, Carbon
mono oxide, Carbon dioxide, Nitrogen, and Oxygen.These gases are formed
due to the fluxes present on the welding electrode, Moisture, Oil, Grease other
foreign contaminants present on the joint, or on the welding electrode or on
the filler wire. Insufficient flow of shielding gas also causes porosity in
GMAW,FCAW, GTAW & PAW welding processes.
●Prevention:
1.UselowHydrogenelectrode
2.Bakingofelectrodesbeforeweldingaspertherecommendedprocedure
3.Thoroughcleaningofthejointsurfaceandadjacentareabeforewelding
4.Preheatthejointbeforewelding
5.EnsuresufficientflowofshieldinggasesifusingTIGorMIGwelding

11. ●Undercut appears as a narrow groove on the base metal adjacent to the
weld metal along the edge. Undercut always runs parallel to the weld metal.
It acts as a stress raiser during fatigue loading
3. UNDERCUT:

12. ●Causes of Undercut:
1. High welding current and arc
voltage
2. Large electrode diameter
3. Incorrect electrode angle
4. Longer arc length
●Prevent
1.Control Your Arc Length.
2.ControlWeldAngle.
3.ReduceCurrent.
4.Slow Down the Travel Speed.
5.Reducethe Weave Width.
6.Choose the CorrectWeldingPosition.
7.Consider Which Electrode You Are
Using.
8.Allow the Base Metal to Cool.

13. ●When the weld metal surface remains below the adjacent surface of the
base metal then it is called an underfill. Basically, Underfill is undersized
welding.
4. UNDERFILL:

14. cause:
Improper weldingtechniques
Prevention:
Apply proper welding techniques fortheweld
typeandpositionusestrippers bead before the
cover pass.

15. ●When the weld metal doesn’t completely penetrate the joint, then it
is called a Lack of Penetration or Incomplete Penetration. It is one of
the most dangerous defects since it acts as a stress raiser, and hence
crack may originate or propagate from there
5. LACK OF PENETRATION (INCOMPLETE
PENETRATION):
.

16. ●Causes of Lack of Penetration:
1. Root gap too small
2. Fast travel speed
3. Low heat input
4. Too large an electrode diameter
●Prevention:
1. Proper joint preparation i.e.providing a
suitable root gap.
2. Proper heat input
3. Correct travel speed
4. Using electrode of suitable size
●Lack of penetration can be repaired by
proper back gouging.

17. ●tisthelackofpropermelting(orproperfusion)eitherbetweentheweld
metalwiththebasemetaloronelayeroftheweldwiththeotherlayer.Lack
offusionisalsocalledasColdlappingorcoldshuts.Oneofthemost
prominentreasonsforthecauseoflackoffusionispoorweldingtechniques.
Lackoffusionisaninternaldefect,butitcanoccurontheexternalsurface
tooifthesidewallofparentmetaldoesn’tgetproperlyfusedwiththebase
metal,asshowninthebelowfigureandforthiscaselackoffusioncanalso
becalledas‘lackofsidewallfusion’.
●
6. LACK OF FUSION (INCOMPLETE FUSION):

18. ●Causes of Lack of Fusion:
1. Low welding current
2. Travel speed tohigh or too low
3. Unfavorable heat input
●Prevention:
●Eliminate the potential causes
●Maintain proper current and welding speed
●Proper cleaningofeachbead

19. ●Spatters are small globular metal droplets (of weld metal) splashed out on
the base metal during welding. Spatters stick on the base metal hence can be
removed by wire brush or buffing
7. SPATTERS:

20. ●Causes of Spatters:
1. Excessive arc current
2. Excessive long arc
3. Improper shielding gases
4. Electrode with improper flux
5. Damp electrodes
●Prevention
1.should go without saying, you
need to know and understand the
metal you are welding. If it is a
quality material suitable for welding,
spatter will be less.

21. ●Overlap occurs due to the overflow of weld metal on the surface of base
metal. During welding, molten metal overflows on the base metal without
fusing with the base metal.
8. OVERLAP:

22. ●Causes of Overlap:
1. Current too low
2. Large deposition in a single run
3. Longer arc
4. Slow arc travel speed
●Prevention
●1.use a metal type and grademore agreeable
with high-heat conditions
•2.Find a more skilled, experienced welder

23. ●When the penetration of weld metal is too high, through the joints, then it is
called as excessive penetration. It acts as a notch where stress concentration
takes place. In addition to this, it results in economical wastage too.
●
9. EXCESSIVE PENETRATION:

24. ●Causes of Excessive Penetration:
1. Too wide a root gap
2. High welding current
3. Slow travel Speed
●Prevention
1.reduce the amprage
2.use a smaller electrode
3.maintain astableweldingspeed

25. ●Anyentrappedsolidmaterial(eithermetallicornon-metallic)inthe
weldmetal,iscalledasInclusion.Tungsten,Oxides,Slag,andFluxare
someofthecommonforeignmaterialswhichareentrappedinthe
moltenweldpoolandforminclusion.
●Inclusion may occur in most of the fusion welding processes but are very
common in flux shielded arc welding processes such as Shielded metal
arc welding (SMAW),Flux core arc welding (FCAW), and Submerged arc
welding (SAW).
●Tungsten inclusion occurs in those welding processes which use
“Tungsten” as electrodes such as TIG welding and Plasma Arc Welding
(PAW)
10. INCLUSION:

26. 1.Tungsten Inclusion
2.Oxide Inclusion
3.Slag Inclusion
4.Flux Inclusion
●When slag gets entrapped and doesn’t get a chance to escape from the
molten weld pool then such inclusion is called asSlag Inclusion.Similarly,
sometimes droplets of tungsten get entrapped within the weld metal
resulting inTungsten Inclusion(in TIG welding or Plasma Arc Welding –PAW).
Surface oxides also get entrapped resulting inOxide Inclusion.The words Flux
and slag are often used interchangeably but they are different. Flux is
electrode coating (Solid material which covers the electrode) whereas, Slag is
a byproduct formed by the reaction between flux and the molten weld pool
metal.
●nclusionacts as a stress raiser hence should be avoided.
Inclusions are of four types, these are;

28. ●Linear slag inclusion along the axis of the weld is called as wagon tracks.
Duringroot pass, a groove is formed at the toe, due to wrong welding
techniques, and that groove is filled by slag (especially Hydrogen which
has been trapped by the solidified slag) and thus wagon tracks are formed.
It is also known as worm tracks.
11. WAGON TRACKS:

29. ●Causes wagon track
1.thecounteroftherootpassis
toohigh,
2.the welded toe is not bonded to
the base metal
Prevention
1.use proper techniques to the
deposit weld root

30. ●When the electrode or the electrode holder, unintentionally or
accidentally strikes with the workpiece, an unwanted arc is
generated causing an arc strike. Arc strikes may initiate failure in
bending and cyclic loading. In addition to this, it also affects the
aesthetics of the workpiece.
12. ARC STRIKE:

31. ●Causes of Arc Strike welding defects:
•Access to the welding groove is difficult.
•The coating of the electrode holder is
peeling.
•Wrong laying electrode Holder.
•The clamp at base metal is not good.
●Prevention :
•Access to welding should be easier.
•Periodically check the electrode holder.
•Provides a place to put electrode holder.

32. ●During solidification of the molten weld pool, metal shrinkage
occurs. Due to the shrinkage of weld metal, a cavity is formed
known as the shrinkage cavity.
13. SHRINKAGE CAVITY:

33. prevent
1.Do not overweld.
2.Use intermittentwelding.
3.Use as fewweldpasses as possible.
4.Placeweldsnear the neutral axis.
5.Balanceweldsaround the neutral axis.
6.Use backstepwelding.
7.Anticipate theshrinkageforces.
8.Plan theweldingsequence
cause
1.Metalexpands when it is heated and if heated enough, contracts past
where it was to start.