SS Defects
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Transcript of SS Defects
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Weld Discontinuities and defectsCauses & Remedies DefinitionInfluence TypesCausesRemedies
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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
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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
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Dr.S.SureshSr. Deputy General ManagerWelding Research Institute, BHEL, TrichyWeld Discontinuities and defectsCauses & Remedies
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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
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Weld Strength Lack of penetration Presence of Fusion related discontinuities
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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
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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
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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
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Metallurgical discontinuity Fusion type discontinuity Geometrical discontinuity Types of discontinuities Surface discontinuity Internal discontinuityVoluminar discontinuity Planar discontinuity
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Common surface DiscontinuitiesUn-equal weld sizeUnder sized weldWeld offset ( from seam) Non-uniform weld size (along the length)Oversized weld Excess Penetration Weld crater
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Common surface DiscontinuitiesImproper Weld bead Profile Coarse weld Ripples Excess ConvexityRoot concavityExcess ReinforcementOverlapUndercutMisalignmentLack of Penetration
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Common Surface DiscontinuitiesSurface PorositySpatterWire stickingCrater pin holeCrater crackSurface cracks
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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
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Gouges & defects on Gas cut surfaces
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Arc strikes & Spatter
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Excess PenetrationProper Penetration Excess Penetration P
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Excess Penetration
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Root Concavity
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Weld Size & Reinforcement R = max 3 mm
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Shallow Obtuse angle > 100 Obtuse angle > 90Acute angle > 90High level of SCWeld Size & Reinforcement
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Weld Size & Reinforcement
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Weld bead ProfileFillet Weld with straight bead Fillet Weld with Convex bead Fillet Weld with Concave bead
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Weld Bead Profile
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Undercut & Bead Off-set
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Undercut - Causes
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Mis-alignment
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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
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Surface Porosity & Slag
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Types of Porosity Distributed PoresAligned PoresClustered Pores
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Internal Porosity
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Types of Porosity Cluster & distributed
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Types of Porosity Aligned
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Aligned Porosity
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Pin-hole PorosityStart Stop Porosity
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Worm-Hole Porosity
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Slag Inclusion
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Slag Inclusion
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1-Incomplete fusion 2-Linear slag Inclusion3-Crack
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Incomplete fusion -Causes
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1-Excessive Penetration2-slag InclusionGas Pores
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LOP1-Lack of penetration between runs2-LOP at side wall
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1-Linear Slag inclusion2-Lack of fusion3-Weld metal crack
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Lack of fusion
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Lack of Penetration
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Cold Cracking (Under bead cracking)HAZ
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Cold Cracking (Under bead cracking)
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Lamellar Tearing
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Cold Cracking (Under bead cracking)
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Cracking
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10 mmHot Cracking
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Hot Cracking
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Types of defects
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Types of Cracking