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Common Weld Discontinuities
Common Weld Discontinuities
Gas Pore
Gas pore A cavity, generally formed by trapped gas during the solidification of molten metal
Cluster Porosity A group of gas pores
Porosity
Crater Pipe (GTAW)
AMIT PAHUJA QA QC NDE WELDING at SADARA
Crater Pipe
Crater pipe A depression due to shrinkage at the end of a run where the source of heat was removed. Crater pipes may also lead to micro-cracking
AMIT PAHUJA Welding Engineering at SADARA
Porosity
Causes of Porosity Insufficient Protection/wind/Tent Insufficient interpass cleaning Unsteady travel speed Welding weave too wide Allowing slag to run ahead of the arc Using too large and electrode Damp electrode
Slag Inclusions
Causes of Slag Inclusions
Base Metal contaminated Wet, unclean electrodes Insufficient or damp shielding gas Excessive arc length Welding current too high Weld speed too fast
Incomplete Penetration
Root Defects
Incomplete root penetrat ion Failure of weld metal to extend into the root of a joint
Lack of root fusion Lack of union at the root of a joint
Excess penetrat ion bead Excess weld metal protruding through the root of a fusion weld made from one side only
Causes of Incomplete Penetration
Too small a root opening Too large a root face Excessive high low Travel speed too fast Welding current too low Electrode diameter too large Excessive arc length
Causes of Excessive Penetration
Too large a root opening Too small a root face Welding current too high Travel speed too low Arc length too short
Incomplete Fusion Lack of Inter Run Fusion
Causes of Incomplete Fusion
Improper electrode angle Travel speed too fast Welding current too low Faulty joint preparation Electrode diameter too large
Heat Affected Zone
Causes of Cracks
Base metal contaminated Excessive joint restraint Incorrect pre-heat Incorrect filler metal Too fast a cooling rate
Causes of Undercut
Incorrect electrode manipulation
Welding current too high Excessive arc length Travel speed too fast
Tungsten Inclusions
Causes of Tungsten Inclusions
Contact of electrode tip with weld pool Contact of filler metal with tip of electrode Contamination of electrode Exceeding current limit for the electrode Splits or cracks in tungsten electrode
Visual Inspection of Welds
Overlap Good Fillet Weld
Overlap An imperfection at the toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it
Arc Strike
Stray f lash/arc burn/arc strike (stray arcing) 1. The damage on the parent material resulting from the accidental striking of . an arc away from the weld2. The accidental str iking of an arc away from the weld
Spatters
Effect of Current, Speed, Arc-length
Weld Width
For butt welds and f i l let welds, consider:
Weld width and consistency of weld width
Butt Weld Size
a) excess weld metal height
b) root penetrat ion
c) weld width
d) root bead width
Shape (Butt Welds)
Ideally, (a) is the most desirable
Consider:
Bulbous Contour
Bulbous contour poor appearance
Contour Defects
Incompletely fi l led groove A continuous or intermittent channel in the surface of a weld, running along its length, due to insufficient weld metal. The channel may be along the centre or along one or both edges of the weld
Root DefectsRoot concavity (suck-back;)A shallow groove which may occur in the root of a butt weld, but full fusion is evident
Shrinkage groove A shallow groove caused by contraction in the metal along each side of a penetration bead or along the weld centreline
Burnthrough (melt through)A localised collapse of the molten pool due to excessive penetration, resulting in a hole in the weld run
Toe Blend (Butt Welds)
Depending on the service conditions of the product, the toe blend may be of greater importance than the size and shape of the weld. A poor toe blend may reduce service life by a considerable margin if the product is under a cyclic load.
For butt welds, consider :
In normal practice, (a) is the most desirable but, again, in many instances it is difficult to achieve.
Toe Blend (Fillet Welds)For f i l let welds, consider:In normal practice, (a) is the most desirable but, again, in many instances it is difficult to achieve. Acceptance levels, therefore, allow tolerances on weld shape.
Perfect Weld Bead Appearance SMAW/GTAW
Perfect Weld Bead Appearance Fillet Weld
Good Weld Bead Finish GTAW/SMAW
Thank You