| We've compiled a list of the most common weld discontinuities and how to correct them. A discontinuity is a flaw in the weld, but they are only considered to be weld defects when they exceed the limit allowed by the welding code. Learn more about welding codes here. Each code determines the extent of the discontinuity before it is classified as a defect and must be repaired. For example, if a welding code acceptance criteria allows for undercut up to 1/32" deep and the welding inspector measures undercut that is 1/16" deep, then that weld is rejectable. If the undercut measured was 1/32" or less, then the weld is acceptable. All defects are discontinuities, but not all discontinuities are defects. Understanding this forms the key to the proper analysis of any weld performed in accordance with the requirements of a welding code or specification. |
Porosity
 | Porosity is a cavity-type discontinuity caused by trapped gas in the weld during the solidification of the weld metal. Possible Causes Long Arc Length Dirty Base Metal Inadequate Gas Coverage Possible Cures Use Proper Arc Length Clean Base Metal Check for Proper Gas Coverage |
Undercut
 | Undercut is a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal. Possible Causes Improper Welding Technique Excessive Voltage Too low wire feed speed Possible Cures Reduce Arc Length Reduce Travel Speed Use Proper Electrode Angle |
Incomplete Fusion
 | Incomplete fusion is a weld discontinuity in which fusion didn't occur between the weld metal and the fusion faces or the adjoining weld beads. Possible Causes “Cold” Welding Procedures Travel Speed Too Slow Travel Speed Too Fast Possible Cures Increase Current Use Proper Travel Speed |
Incomplete Joint Penetration
 | Incomplete joint penetration is a joint root condition in a groove weld in which weld metal does not extend through the joint thickness. Possible Causes “Cold” Welding Procedures Travel Speed Too Slow Travel Speed Too Fast Improper Joint Detail Possible Cures Increase Current Use Proper Travel Speed |
Excessive Reinforcement
 | Excessive reinforcement is a discontinunity caused by the weld being too big or has too much build up. Possible Causes Travel Speed Too Slow “Cold” Welding Procedures Possible Cures Increase Travel Speed Increase Current |
underfill
 | Underfill is a groove weld condition in which the weld face or root surface is below the adjacent surface of the base metal. Possible Causes Insufficient Weld Metal Possible Cures Reduce Travel Speed |
Concave Root Surface (Suck-back)
 | Concave root surface is a groove weld exhibiting underfill at the root surface. Possible Causes Too Much Current Arc Length Too Long Root Face Too Small Possible Cures Reduce Current Maintain Proper Arc Length Use Proper Joint Fitup |
Overlap
 | Overlap is extra filler metal that spreads out beyond the weld bead. Possible Causes Travel Speed Too Slow Possible Cures Use Proper Travel Speed |
Arc Strikes
 | Arc strike is considered a weld discontinuity resulting from an arc. Possible Causes Improper Welding Technique Possible Cures Initiate Arc Inside the Weld Joint |
Slag Inclusions
 | Slag inclusions are a weld discontinuity consisting of slag entrapped in weld metal or at the weld interface. Possible Causes Improper Welding Technique Possible Cures Use Correct Welding Technique Clean Weld Between Passes |
Earlbeck Technical Center
Still need some help? The Earlbeck Technical Center offers welder training and weld testing services in the Mid-Atlantic Area. Not only do we conduct testing services to any code, but we provide training to ensure you are ready to take your certification test. Click here to learn more.
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