Weld Overlap: Causes, Risks, Inspection and Acceptance Criteria
Many people think weld overlap is only a surface problem. Some people think they can simply grind it away. This is not correct. AWS and ASME standards do not accept overlap because it is a lack of fusion defect. The weld must be removed and welded again.
What Is Weld Overlap?
Weld overlap happens when the molten weld metal flows onto the base metal but does not fuse with it at the weld toe. The weld may look smooth, but there is no metallurgical bond. This leaves a weak edge on the joint.
What Causes Weld Overlap?
Overlap often comes from incorrect welding settings or poor welding skills. Common causes include:
- Low heat input
- Too much filler metal
- Wrong torch or electrode angle
- Slow travel speed
- Poor weld pool control
Good welding practice and the correct welding parameters can help prevent this defect.
Why Is Weld Overlap Dangerous?
Overlap is not only a surface defect. It can reduce the strength of the welded joint. It can also:
- Create stress concentration
- Increase the risk of faTIGue cracks
- Cause corrosion under insulation (CUI)
- Create a path for leakage
These problems can shorten the service life of the welded structure.
How to Inspect Weld Overlap
Visual Testing (VT) is the main inspection method because overlap is on the surface. Magnetic Particle Testing (MT) and Penetrant Testing (PT) can also find lack of fusion at the weld toe. Radiographic Testing (RT) and Ultrasonic Testing (UT) are not good at finding overlap.
Acceptance Criteria
Major welding standards do not allow overlap.
- AWS D1.1: Overlap is not acceptable.
- ASME B31.3: Surface lack of fusion defects must be rejected.
- ASME Section IX: Overlap is not acceptable and the weld must be removed and welded again.
Conclusion
Weld overlap is not a small problem. It is a lack of fusion defect that can cause cracks, corrosion, leaks, and weld failure. Grinding the surface is not enough. The correct repair is to remove the defective weld and reweld it with the correct welding procedure.