Weld Discontinuities and defectsCauses & Remedies DefinitionInfluence TypesCausesRemedies

Discontinuity & Defect Discontinuity refers to any interruption or in-homogeneity in the material that is otherwise homogenous Defect refers to an interruption having dimensions/features beyond acceptable limits.Defects are otherwise called as Flaw or Imperfections that are to be repaired so that the material is made more homogeneous as assumed in the design

Weld joint is itself is a Discontinuity The Microstructure is different in the different regions of weld zones of weld joint.So the mechanical properties also vary from zone to zone causing heterogeneity PMWMHAZHAZ

Dr.S.SureshSr. Deputy General ManagerWelding Research Institute, BHEL, TrichyWeld Discontinuities and defectsCauses & Remedies

Discontinuity & Strength Strength of the weld joint is influenced by Filler metal strength The extent of penetration Presence of discontinuities in the weldPresence of stresses in the weld jointtt

Weld Strength Lack of penetration Presence of Fusion related discontinuities

Weld Strength 100% Joint Efficiency is obtained when The weld is carried out on both sides Back gouging is done after welding the first sideLPI or MPT is carried out after Back gouging100% RT / UT is carried out after second side welding

Weld Strength The Electrode or the filler wire should be selected such that it Matches with the strength of the base materialHas fairly low carbon & controlled impurities to avoid crackingMoisture level is controlled and is of low H2 typeIs usable in all positions

Influence of discontinuities They act as stress raisers They reduce the cross sectional area and thereby increase the stress concentration around them They provide a leak path They are potential sites of crack initiation They act as potential sites of corrosion and erosion

Metallurgical discontinuity Fusion type discontinuity Geometrical discontinuity Types of discontinuities Surface discontinuity Internal discontinuityVoluminar discontinuity Planar discontinuity

Common surface DiscontinuitiesUn-equal weld sizeUnder sized weldWeld offset ( from seam) Non-uniform weld size (along the length)Oversized weld Excess Penetration Weld crater

Common surface DiscontinuitiesImproper Weld bead Profile Coarse weld Ripples Excess ConvexityRoot concavityExcess ReinforcementOverlapUndercutMisalignmentLack of Penetration

Common Surface DiscontinuitiesSurface PorositySpatterWire stickingCrater pin holeCrater crackSurface cracks

Common Internal DiscontinuitiesPorosityBlow Holes / Aligned / distributed / Cluster / worm hole PorositiesLack of fusion/ Lack of Penetration Lack of side wall fusion / Inter run fusion / lack of fusion at rootCrackingUnder-bead cracking / delayed cracking / Delayed cracking /Hydrogen induced crackingHot cracking, shrinkage cracks, Fatigue cracking

Gouges & defects on Gas cut surfaces

Arc strikes & Spatter

Excess PenetrationProper Penetration Excess Penetration P

Excess Penetration

Root Concavity

Weld Size & Reinforcement R = max 3 mm

Shallow Obtuse angle > 100 Obtuse angle > 90Acute angle > 90High level of SCWeld Size & Reinforcement

Weld Size & Reinforcement

Weld bead ProfileFillet Weld with straight bead Fillet Weld with Convex bead Fillet Weld with Concave bead

Weld Bead Profile

Undercut & Bead Off-set

Undercut - Causes

Mis-alignment

Porosity - Cause /SourceMoisture in Plate edgesNon-baked/dried Electrodes Filler wireWet / Non-dried flux Pneumatic fixture In the atmosphereInadequate Gas shielding due to Improper setting of gas flow rates Improper Torch angles Improper setting of welding ParametersCavities / voids formed due to entrapment of gases when the molten metal solidifies from liquid state when more gases get dissolved into molten metal

Surface Porosity & Slag

Types of Porosity Distributed PoresAligned PoresClustered Pores

Internal Porosity

Types of Porosity Cluster & distributed

Types of Porosity Aligned

Aligned Porosity

Pin-hole PorosityStart Stop Porosity

Worm-Hole Porosity

Slag Inclusion

Slag Inclusion

1-Incomplete fusion 2-Linear slag Inclusion3-Crack

Incomplete fusion -Causes

1-Excessive Penetration2-slag InclusionGas Pores

LOP1-Lack of penetration between runs2-LOP at side wall

1-Linear Slag inclusion2-Lack of fusion3-Weld metal crack

Lack of fusion

Lack of Penetration

Cold Cracking (Under bead cracking)HAZ

Cold Cracking (Under bead cracking)

Lamellar Tearing

Cold Cracking (Under bead cracking)

Cracking

10 mmHot Cracking

Hot Cracking

Types of defects

Types of Cracking