Discontinuity
Overlap
Weld metal that has rolled over the toe and sits on unmelted base metal, forming a lip with a sharp crevice underneath that carries no load and hides an unfused interface.
What it looks like
- A rounded lip of weld metal protruding past the toe and resting on the plate surface
- A tight dark crevice under the lip where weld metal never fused to the base metal
- Most common on the lower toe of horizontal fillets, where gravity pulls the puddle down
- Gives a deceptively full, well-fed appearance that can be mistaken for a generous weld
Causes
- Current too low to melt the base metal while filler is still being deposited
- Travel speed too slow, letting the puddle grow and run ahead of the arc onto cold metal
- Incorrect electrode angle that pushes the puddle sideways instead of driving the arc into the toe
- Excessive deposition rate for the joint, overfilling faster than the base metal can be fused
- Gravity in horizontal and overhead work pulling a fluid puddle over the lower toe
Prevention
- Raise current or speed up travel so the arc melts the joint face rather than burying it
- Keep the arc on the leading edge of the puddle so the puddle never runs ahead of the heat
- Use smaller beads and multiple passes rather than one oversized pass in out-of-position work
- Adjust work angle in horizontal fillets to hold the puddle up against the vertical member
How it is found
- VT
- The rolled lip and the crevice beneath it are visible at the toe, and a straightedge or fillet gauge shows the profile clearly.
- PT
- Penetrant enters the crevice under the lip and bleeds out, marking the unfused interface that visual inspection alone may miss.
- MT
- The unfused interface under the lip disturbs the magnetic field on steel and holds particles along the toe line.
How inspectors think about it
- Overlap is generally treated as unacceptable regardless of size, because the metal lying over the toe adds no strength while creating a notch that concentrates stress.
- It is really a fusion problem wearing a profile problem's clothing, so inspectors read it as evidence of low heat input or poor manipulation rather than cosmetics.
- Because the fault is at the surface, correction usually means grinding the lip away and confirming the underlying toe is fused, not simply adding more weld.
General reasoning only. The accept/reject limits for your work come from the code or specification governing the job, which this site does not reproduce.
Related discontinuities
UndercutA groove melted into the base metal at the weld toe and left unfilled by weld metal, reducing the section of the parent material and leaving a sharp notch exactly where stress concentrates.Incomplete fusionWeld metal that lay against the joint face or a previous bead without melting into it, leaving a tight unbonded plane that carries no load even though the joint looks completely filled.Excessive reinforcementA weld face built up far higher than the joint needs, producing an abrupt change of section at the toes that concentrates stress despite the extra metal looking like extra strength.Toe crackA crack starting at the junction of the weld face and the base metal, where the abrupt change in section concentrates stress and the heat-affected zone is at its hardest and least forgiving.
Can you name it on sight?
The gauge trainer's identification mode shows you a weld and four names. Reading about porosity and picking it out of a line-up are not the same skill.