§3.1C · Under Visual examination
Incomplete fusion vs incomplete joint penetration
Incomplete fusion and incomplete joint penetration both get called lack of something on the floor, and they're easy to mix up when both turn up in the same root. Fusion asks whether the weld metal bonded to the joint face or the bead next to it. Penetration asks how deep into the joint the weld got, measured against the joint thickness.
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- Visual examination
3.1C.1Fusion vs penetration
| Point | Incomplete fusion | Incomplete joint penetration |
|---|---|---|
| A3.0 idea | No bond where weld metal meets a fusion face or another bead | Weld metal short of extending through the joint thickness |
| Where | Sidewalls, between passes, at a root face | At the root of a groove weld |
| Shape | Flat, following the bevel or a bead boundary | Along the root, often straight and continuous |
| Usual causes | Low heat at the face, poor electrode or gun angle, a weave too wide, scale or oxide on the bevel | Root face too thick, root opening too tight, bevel angle too small, back gouge too shallow |
| Visual finds it | Only where it reaches the surface | From the root side, if you can see it |
| On a PJP joint | Still a discontinuity | The unwelded part is the design, so check the weld size instead |
≠ marks a row where the two differ.
3.1C.2Telling them apart
Both belong to the visual examination clause, though visual only catches them where they reach a surface. The tell is location and direction. A flaw that follows a bevel face, or the line between two beads, is incomplete fusion at whatever depth it sits. A gap at the bottom of the joint, where the weld was supposed to reach the far side, is incomplete joint penetration.
On film they look different too. Incomplete joint penetration usually shows as a straight, dark line along the middle of the root. Incomplete fusion on a sidewall, when RT picks it up at all, shows as a thin line running off to one side, along the bevel edge.
The two can share a spot. A root pass that melted into one root face and not the other has both: no fusion on one face, and a joint that wasn't penetrated through. Name the one the situation is asking about.
CJP or PJP decides whether it's a problem
Incomplete joint penetration only exists against a requirement. On a CJP joint, any root short of full thickness counts. On a PJP joint the unwelded portion is intended, and you check that the groove weld size on the symbol was reached. The groove weld symbols page shows how the drawing tells you which one you have.
Two sides of the cause
Heat and angle are the welder's side; heat input and technique sit in welding application and control. Fit-up is yours. Check root face, root opening and bevel angle before the root pass goes in, because technique can't rescue a joint prepped too tight.
3.1C.3Finding them once the cap is on
3.1C.4Bond or depth?
Spotting, causing and writing up both conditions.
0 of 6 tagged · 0 accepted
Tag 01
Which condition best indicates incomplete fusion in a weld?
Remarks on every option
- A Correct: Incomplete fusion means weld metal didn't fuse to the fusion face or the next bead. It's a missing bond, not missing depth.
- B Spatter is a cleanup issue. It isn't incomplete fusion.
- C Pinholes are surface porosity: trapped gas, not missed fusion.
- D Too much reinforcement is a profile problem, not a fusion problem.
Pick an option. The remarks on all 4 open here.
Tag 02
Which visual characteristic indicates possible lack of fusion in a multi-pass weld?
Remarks on every option
- A Rough ripples come from technique. They don't prove fusion was missed.
- B Correct: A visible line or groove where a pass meets the bead or sidewall before it points to incomplete fusion between them.
- C Color reflects heat and shielding, not whether the passes fused.
- D Uneven width is a workmanship issue. By itself it doesn't show lack of fusion.
Pick an option. The remarks on all 4 open here.
Tag 03
What is the primary purpose of examining weld root penetration?
Remarks on every option
- A The cap is the other side of the joint. Root checks are about whether the weld reached and fused the bottom.
- B Color says something about shielding, not whether the root fused through.
- C Face reinforcement is measured on the face side. Root checks are about penetration and fusion at the bottom.
- D Correct: Root checks confirm the weld metal reached the bottom of the joint and fused both root faces, so no incomplete penetration and no unfused root edge.
Pick an option. The remarks on all 4 open here.
Tag 04
Which welding defect is most likely to occur when travel speed is too fast?
Remarks on every option
- A Crater cracks come from a poor stop with the crater left unfilled, not from travel speed.
- B Porosity is mostly a shielding or contamination problem. Fast travel can add to it, but missed fusion is the main result.
- C Correct: Travel too fast and the arc doesn't have time to melt into the base metal or the bead before, so you get incomplete fusion.
- D Slag inclusions come mainly from poor cleaning, or slow travel letting slag run ahead of the puddle.
Pick an option. The remarks on all 4 open here.
Tag 05
What term describes the complete penetration through the joint thickness?
Remarks on every option
- A Not the AWS term, and it mixes up fusion with penetration.
- B Correct: Complete joint penetration (CJP) is weld metal extending through the full thickness of the joint.
- C Not a standard term. The AWS term is complete joint penetration.
- D Not a standard term. Root penetration is only how far the weld reached past the root.
Pick an option. The remarks on all 4 open here.
Tag 06
How should the extent of incomplete penetration be documented?
Remarks on every option
- A Length alone doesn't say where it is or how deep. A repair crew needs all three.
- B Width isn't the dimension that matters here. Where it is and how deep it goes do.
- C Noting that it's there isn't enough to evaluate it or find it for repair.
- D Correct: Record where it is, how long it is and how deep it goes (where the method can tell), so it can be judged and repaired.
Pick an option. The remarks on all 4 open here.
3.1C.5Fusion or penetration: quick answers
Is lack of fusion the same as incomplete fusion?
Yes. Lack of fusion is the common shop and search term. A3.0 treats it as nonstandard and uses incomplete fusion, so use that on the exam.
Is lack of penetration the same as incomplete joint penetration?
Same idea, older wording. A3.0 uses incomplete joint penetration, and its opposite is complete joint penetration (CJP).
Which NDE finds incomplete fusion best?
UT, because incomplete fusion is planar. RT can miss a sidewall that isn't lined up with the beam. Incomplete joint penetration usually shows on RT as a dark line along the root.
How is either one repaired?
Usually by removing the affected weld metal and rewelding under the governing code's repair rules. The repair is then inspected to the same acceptance criteria as the original weld.
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