Weld Defect Identification Guide
A visual reference for common welding defects, what causes them, and how to fix them - based on AWS B4.0 standards
Why Defect Identification Matters
If you are going to pass a weld test or work as a welder, you need to know what makes a weld rejectable. This guide covers the most common defects, what they look like, and how to avoid them.
This is also what DimeVision checks when you upload a photo.
1. Porosity
Small holes or cavities in the weld metal.
Types: Distributed, cluster, linear, root porosity
caused by:
- Contaminated base metal (oil, rust, paint)
- Wet or contaminated filler metal
- Travel speed too fast
- Excessive wind or drafts
Fix: Always clean base metal with a grinder. Store filler metal properly. Slow down. Use wind shield outdoors.
2. Lack of Fusion
The weld metal did not fully fuse with the base metal or previous pass.
caused by:
- Insufficient heat (amps too low)
- Travel speed too fast
- Incorrect torch angle
Fix: Increase amperage 10-15%. Reduce travel speed. Keep torch at 15-20 degrees.
3. Undercut
A groove melted into the base metal adjacent to the weld toe.
caused by:
- Arc length too long
- Travel speed too slow
- Incorrect torch angle
Fix: Keep arc length short. Increase travel speed. AWS D1.1 limit: 1/32 inch maximum.
4. Overlap
The weld metal extends over the weld toe without fusion.
caused by:
- Insufficient heat
- Travel speed too slow
- Wrong torch angle
Fix: Increase amperage. Adjust torch angle. Place filler correctly.
5. Excessive Reinforcement
The weld crown is taller than allowed.
Fix: Use stringer beads. Increase travel speed. Typical max: 1/8 inch per AWS D1.1.
6. Crater Cracks
Cracks in the crater at the end of a weld bead.
Fix: Do not stop abruptly. Use crater fill technique. Backstep 1/4 inch before lifting.
7. Spatter
Metal particles expelled during welding that adhere to surrounding areas.
Fix: Balance wire feed with voltage. Replace worn contact tips. Clean base metal.
8. Incomplete Penetration
The weld did not extend through the entire joint thickness.
Fix: Ensure adequate root opening (1/16 to 1/8 inch). Increase amperage for root passes. Slow down at root.
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Quick Reference
| Defect | Main Cause | Quick Fix |
|---|
| Porosity | Contamination, speed | Clean metal, slow down |
| Lack of Fusion | Low heat, fast travel | Increase amps |
| Undercut | Long arc, slow travel | Short arc, go faster |
| Overlap | Low heat, wrong angle | More heat, adjust angle |
| Excessive Reinforcement | Too much filler | Faster travel |
| Crater Cracks | Abrupt stop | Crater fill technique |
| Spatter | High wire speed | Balance wire/voltage |
| Incomplete Penetration | Root too tight | Open root gap |
Sources
- AWS D1.1-2020, Structural Welding Code-Steel
- AWS B4.0, Standard Methods for Visual Examination of Welds
- Lincoln Electric Technical Guide
- Miller Welder Resources