Problem: Undercut
Undercut is an appearance defect, not a structural detriment. However under some service conditions an undercut may start a fatigue crack. Unfortunately, some inspection agencies are against undercut of any type and demand that it be chipped out and the joint rewelded. For this reason, undercut should be avoided.
Causes of undercut are:
- Welding current too high.
- Electrode diameter too large.
- Improper electrode manipulation.
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To prevent undercut:
- Use a moderate welding current and do not try to weld too rapidly.
- Use a smaller diameter electrode.
- Don't let the molten weld puddle get too large. A uniform weave of the electrode will tend to prevent undercutting when making butt welds. Excessive weaving will cause undercut and should be avoided. Undercut on the vertical plate when making a horizontal fillet weld is caused by the electrode being held too near the vertical plate.
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