Why it matters
Defect questions ask you to name a discontinuity from a description, or pick its most likely cause. Learn each defect together with the one or two settings or habits that cause it.
Key points
- Porosity: gas trapped in the weld. Look at shielding gas flow, drafts, damp electrodes and dirty base metal.
- Undercut: a groove melted into the base metal at the toe. Usually too much current, too long an arc or wrong angle.
- Incomplete fusion: weld metal not fused to the base metal or previous pass. Often too little heat or too fast travel.
- Slag inclusion: slag trapped between passes. Clean thoroughly between passes.
- Cracks are the most serious defect. Hydrogen, restraint and fast cooling all play a part, so preheat and low-hydrogen practice help.
Study tip
When a question gives several causes, pick the one that changes the heat or the shielding, since that is what the exam usually tests.
Try these
Scattered round holes in a GMAW weld most likely mean:
- Too little wire feed
- Loss of shielding gas
- Too slow travel
- Wrong polarity on SMAW
Show answer
B. Loss of shielding gas Porosity on GMAW is most often a shielding problem.
Undercut is best corrected by:
- Raising the current
- Lengthening the arc
- Lowering current and correcting the angle
- Skipping interpass cleaning
Show answer
C. Lowering current and correcting the angle Too much heat and poor angle cause undercut.
Low-hydrogen electrodes are stored in a heated oven mainly to prevent:
- Spatter
- Hydrogen cracking
- Arc blow
- Undercut
Show answer
B. Hydrogen cracking Moisture in the flux adds hydrogen to the weld.
Keep going
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