Discontinuity
Misalignment (high-low)
Two members offset from one another across the joint so their surfaces do not line up, forcing load to change path through the weld and often leaving part of one root face unfused.
What it looks like
- A visible step across the joint where one plate or pipe wall sits above the other
- Uneven weld toes, with more reinforcement on the low side to bridge the step
- On the root side of pipe, part of one land is shielded from the arc and stays unfused
- On film, a change of density across the joint reflecting the differing thickness in the beam path
Causes
- Poor fit-up and inadequate use of alignment clamps, bridge clamps, or internal line-up devices
- Dimensional differences between members, such as pipe with different wall thickness or ovality
- Distortion during tacking that pulls the members out of line before welding starts
- Tacks that were too small or too few to hold alignment against shrinkage
- Cut edges that are not square, so the parts sit skewed even when clamped
Prevention
- Check alignment with clamps and gauges before tacking, and re-check after tacking is complete
- Use enough tacks of adequate size, placed in a balanced sequence around the joint
- Verify member dimensions and squareness of cut edges before fit-up rather than after
- Apply internal alignment tooling on pipe where wall thickness or ovality varies
How it is found
- VT
- The offset is a dimensional condition at the surface, so a straightedge or hi-lo gauge measures it directly before welding even starts.
- RT
- The density step across the joint on film reveals internal misalignment on pipe where the root side cannot be seen.
- UT
- Confirms whether the offset has left an unfused root face, which is the structural consequence that matters most.
How inspectors think about it
- Misalignment is judged against the thickness of the thinner member, because the same offset is far more significant on light material than on heavy sections.
- The real concern is what the offset does to the load path: an eccentric joint puts bending into a connection that was designed for direct tension.
- It is one of the few conditions best caught before welding, so inspectors treat fit-up examination as the point of control rather than post-weld assessment.
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
Incomplete joint penetrationA groove weld that did not reach through the joint as the design required, leaving unfused root faces and an effective throat smaller than the drawing calls for.UnderfillA groove weld whose face or root sits below the surface of the adjoining base metal, so the joint has less cross-section than the surrounding material it is supposed to match.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.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.
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.