3.4 Acceptance Criteria & Retesting Rules for Welders
Key Takeaways
- Visual acceptance (6.4): no cracks, no inadequate penetration, no burn-through on butt welds, and undercut within the Table 8 tiers — depth > 1/32 in. (0.8 mm) or > 12.5% of wall (whichever is smaller) is never acceptable.
- Nick-break acceptance (6.5 referencing 5.6.3.3): complete penetration/fusion; gas pockets ≤ 1/16 in. (1.6 mm) and ≤ 2% combined area; slag ≤ 1/32 in. (0.8 mm) deep, ≤ 1/8 in. (3 mm) or half wall long, ≥ 1/2 in. (13 mm) separation.
- Bend acceptance (5.6.4.3): no crack or open flaw over 1/8 in. (3 mm) or half the wall thickness in any direction; corner cracks under 1/4 in. (6 mm) disregarded unless they contain obvious imperfections.
- Retesting (6.7): a welder who fails for reasons beyond their control may get a second opportunity by mutual company/contractor agreement; further retests require documented additional welder training acceptable to the company.
- Requalification is required when an essential variable changes, when the company questions the welder's competence (6.8), or — by federal regulation — after a 6-month lapse in tested production welding (49 CFR 192.229 / 195.222).
Last updated: August 2026
3.4 Acceptance Criteria & Retesting Rules for Welders
To pass performance qualification under API 1104:2021 Section 6, a test weld must clear the visual gate (6.4) and then the destructive (6.5) or NDT (6.6) acceptance standards. This section collects the quantitative limits and the retest rules that follow a failure.
1. Visual Acceptance (6.4)
- Cracks and inadequate penetration: zero tolerance.
- Appearance: neat and workmanlike, acceptable to the company; all WPS dimensional requirements met.
- Burn-through: none permitted on butt welds; branch connections allow no BT longer than 1/4 in. (6 mm), with a 1/2 in. (13 mm) aggregate cap per 12 in. (300 mm).
- Undercut (per 9.7 / Table 8):
| Depth | Disposition |
|---|---|
| > 1/32 in. (0.8 mm) or > 12.5% of wall thickness, whichever is smaller | Not acceptable |
| > 1/64 in. (0.4 mm) to ≤ 1/32 in. (0.8 mm), or > 6% to ≤ 12.5% of wall, whichever is smaller | Acceptable up to 2 in. (50 mm) in a continuous 12 in. (300 mm) weld, or one-sixth the weld length, whichever is smaller |
| ≤ 1/64 in. (0.4 mm) or ≤ 6% of wall, whichever is smaller | Acceptable regardless of length |
2. Destructive Acceptance (6.5)
Nick-Break (via 5.6.3.3)
- Complete penetration and fusion across the exposed fracture.
- Individual gas pocket ≤ 1/16 in. (1.6 mm); combined gas-pocket area ≤ 2% of the exposed surface.
- Slag inclusions ≤ 1/32 in. (0.8 mm) deep and ≤ 1/8 in. (3 mm) or one-half the wall thickness in length, whichever is smaller; adjacent inclusions separated by ≥ 1/2 in. (13 mm) of sound metal.
- Fisheyes are not cause for rejection; nick-break specimen replacement is not permitted.
Guided-Bend (via 5.6.4.3 / 5.6.5.3)
- No crack or open flaw exceeding 1/8 in. (3 mm) or one-half the wall thickness, whichever is smaller, in any direction, in the weld or at the fusion zone.
- Corner cracks < 1/4 in. (6 mm) are disregarded unless they contain obvious imperfections.
- One failed bend specimen may be replaced by a single adjacent specimen only when the company judges the flaw unrepresentative.
| Test | Defect | Limit |
|---|---|---|
| Visual | Cracks / IP / BT (butt weld) | Zero |
| Visual (Table 8) | Undercut depth | ≤ 1/32 in. (0.8 mm) or 12.5% wall, smaller value; deeper = reject |
| Nick-break | Gas pocket | ≤ 1/16 in. (1.6 mm); ≤ 2% combined area |
| Nick-break | Slag | ≤ 1/32 in. deep; ≤ 1/8 in. or t/2 long; ≥ 1/2 in. separation |
| Bend | Open flaw | ≤ 1/8 in. (3 mm) or t/2, smaller value |
3. Retesting After Failure (6.7)
The 22nd edition rule has two steps:
- Second opportunity. If, in the mutual opinion of the company and the contractor's representatives, the welder failed because of unavoidable conditions or conditions beyond the welder's control, the welder may be given a second opportunity to qualify.
- Training before further retests. No further retests are given until the welder submits proof of subsequent welder training acceptable to the company.
If the company elects both NDT and destructive testing on the same test joint, failing either acceptance standard fails the weld.
4. When Requalification Is Mandatory
- Essential variable change (6.2.2): process, direction, Table 4 filler group, OD group, thickness range, position, joint design, backing, or pass-combination rules.
- Questioned competence (6.8): the company may require requalification whenever a question arises about the welder's competence — e.g., a pattern of rejectable production welds.
- Regulatory continuity: under 49 CFR 192.229 (gas) and 195.222 (liquids), a welder may not weld on a U.S. regulated pipeline unless at least one of the welder's welds was tested and found acceptable within the preceding 6 calendar months. A lapse forces requalification before the welder returns to production.
Related Disqualification Rules
- Bend behavior: welds are not rejected solely because a specimen fails to bend to the full U-shape; specimens that crack are broken apart and accepted when the exposed surfaces meet the 5.6.3.3 soundness requirements (6.5).
- Full-section tensile option: for pipe at or below 1.315 in. (33.4 mm) OD, the company may qualify the welder with one full-section tensile specimen; if it breaks in the weld or at the weld/parent junction and fails the 5.6.3.3 soundness requirements, the welder is disqualified.
- Dual evaluation: when the company elects both NDT and destructive testing of the same test joint, failure of either acceptance standard fails the weld (6.7).
- Records tie-in: every test and its detailed results are recorded (6.8), and the company keeps the current list of qualified welders and their procedures — an inspector auditing a crew starts from that list.
Test Your Knowledge
What is the maximum allowable open flaw dimension on a guided-bend specimen for welder qualification under API 1104?
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Test Your Knowledge
A welder fails a qualification test when the test booth power source fails mid-weld. What does API 1104:2021 Section 6.7 allow?
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Test Your Knowledge
On a nick-break specimen for welder qualification, what is the maximum allowable individual dimension of a single gas pocket?
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