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