Does AWS D1.1 require a root cause investigation when a crack is found, or just removal and repair?

AWS D1.1 requires complete removal of the crack before rewelding, and the repair must be performed in accordance with a qualified WPS. The standard does not prescribe a formal root cause investigation process, but determining whether the crack is hydrogen-induced, solidification-type, or a recurring pattern is necessary to prevent recurrence and to decide whether the existing WPS is still adequate.

How do you distinguish hydrogen-induced cold cracking from solidification cracking in a production weld?

Solidification (hot) cracking typically appears in the weld metal centerline immediately after the pass is deposited, often while the metal is still at elevated temperature, and shows a dendritic crack surface under magnification. Hydrogen-induced cold cracking (HIC) is delayed — it may not appear until hours after welding — is usually transverse to the weld axis, and occurs in the HAZ or weld metal on steel with higher carbon equivalent. Timing, location, and orientation together distinguish the two types.

Is the original WPS still valid after a weld crack is found?

A single crack does not automatically invalidate a WPS, but a pattern of cracks in the same location, in the same heat of steel, or under the same operator warrants WPS review. If the investigation reveals that preheat was below the WPS minimum, or that the filler metal hydrogen designator was wrong, the WPS procedure compliance — not the WPS itself — was the issue. If the crack type reveals a fundamental WPS inadequacy, requalification may be required.

What records must be kept when a weld crack is repaired under AWS D1.1?

At minimum: the nonconformance report (NCR) identifying the weld, location, and nature of the crack; the repair WPS used; preheat and interpass temperature records for the repair; the welder ID and qualification basis; and post-repair NDE results with acceptance sign-off by the CWI. These records should be tied to the original weld documentation in the project file.

Weld Cracking Investigation Documentation Under AWS D1.1

When a crack is found in a structural weld, AWS D1.1 requires complete removal and corrective action. Here is how to structure the investigation record and disposition trail.

A weld crack found in a structural member is never just a repair task — it is also an investigation. The crack tells you something about what went wrong: preheat that was too low, filler metal that introduced hydrogen, a fit-up gap that put the root in tension during cooling, or a base metal susceptibility that the WPS did not adequately address. AWS D1.1 is clear that all cracks must be completely removed before rewelding, but the code says nothing about the investigation. That gap is where shops fail audits and allow the same failure mode to repeat on the next joint.

Understanding how to document the investigation — and what records to keep — protects the fabricator in claims disputes, demonstrates corrective action during certification audits, and provides the engineering of record with the information they need to evaluate the structure.

Why cracking type matters before you repair

Not every crack is the same, and the appropriate corrective action depends on understanding what caused it. Repairing a hydrogen-induced cold crack without addressing the preheat deficiency that caused it means the repair weld is at risk for the same failure. Two crack types account for the majority of structural weld failures:

Solidification (hot) cracking forms in the weld metal during solidification, typically in the centerline of the weld bead along the solidification grain boundary. It appears while the weld is at elevated temperature — sometimes visible to the CWI during or immediately after welding. Causes include high sulfur or phosphorus in the base metal or filler, concave bead profiles (where the bead width exceeds depth), high heat input producing coarse grains, and highly restrained joints. The crack surface under magnification shows a dendritic, oxidized pattern.

Hydrogen-induced cold cracking (HIC), also called delayed cracking or hydrogen-assisted cracking, develops after the weld has cooled below approximately 200°F (93°C) — sometimes hours or days after welding. It is driven by three factors acting together: susceptible HAZ microstructure (hardness above approximately 350 HV), hydrogen in the weld zone, and tensile stress. HIC is typically transverse to the weld axis (running across the weld), occurs in the HAZ or at the weld root, and may not be visible immediately after welding. This timing is what makes it particularly dangerous on cyclically loaded members — the crack forms during cooling while the structure is being assembled.

Reheat or stress relief cracking forms during PWHT, when the HAZ relaxes residual stress at elevated temperature and does so by crack propagation rather than plastic deformation. This is most common in steels with precipitation hardening alloying additions. It appears in the HAZ, usually at the weld toe, and is associated with PWHT on certain alloy or high-strength grades.

Identifying the crack type before removing it — by documenting its location (centerline, HAZ, root), orientation (longitudinal, transverse, crater), timing (visible immediately vs. found on later inspection), and surface appearance — gives the investigation a starting point.

See: Hydrogen cracking prevention and WPS documentation

AWS D1.1 requirements for crack removal and repair

AWS D1.1:2025 requires that all cracks be completely removed before rewelding. The removal method — typically CAC-A followed by grinding, or grinding alone — must produce a groove that is free of crack indication throughout its depth and length. After removal, PT or MT of the excavated groove is the standard method of confirming that no crack tip remains.

The minimum extent of removal is beyond the crack end in each direction by a margin sufficient to ensure the crack tip is gone. A common practice is to extend the removal at least 1 inch (25 mm) beyond the visual crack end in each direction, then verify by NDE that the endpoint of the excavation shows no indication. If the NDE reveals a remaining indication at the excavated end, the excavation is extended further.

After removal and NDE verification, the repair weld is deposited in accordance with a repair WPS. The repair WPS must be qualified for the base metal, process, filler metal, and the likely geometry of the excavated groove — which may be a partial-depth repair on a previously completed weld. A general production WPS covering standard groove dimensions may not address repair geometry, so many shops maintain a separate repair WPS that explicitly covers partial-depth excavations and unusually wide or deep repair cavities.

See: Repair weld WPS documentation under AWS D1.1

Building the investigation record

The investigation record for a weld crack does not need to be elaborate, but it must be complete enough to support corrective action and to close the nonconformance formally. At minimum, the record should contain:

Identification of the weld. Joint number, weld map reference, welder ID stamp, WPS number used, and date of original welding. This links the crack to a specific work record so the investigation has a starting point.

Description of the crack. Location (HAZ, weld metal centerline, root, toe), orientation (transverse, longitudinal, crater), approximate length and depth if determinable before excavation, and the inspection method that revealed it (visual, MT, PT, UT).

Discovery timing. When was the crack found relative to when it was welded? A crack found during welding in the same pass is very different from one found by UT inspection three weeks later. Timing narrows the likely mechanism significantly.

Condition review. Pull the following from the project records and attach them to the NCR: material test report (MTR) for the base metal used, filler metal certification and lot number, preheat and interpass temperature log for the joint, ambient temperature at the time of welding, and any welder qualification records. If any of these are missing, that gap is itself a finding.

Probable cause determination. Based on crack type, timing, and condition review, state the most likely cause. This can be brief — "HIC probable: preheat was recorded at 150°F against a 200°F WPS minimum; ambient temperature was 28°F; SMAW E7018-H4R electrode used correctly, but preheat was deficient" — but it must be stated. A corrective action that does not identify a cause is not a corrective action.

Corrective action. State what changes will be made to prevent recurrence: preheat verification step added, inspector sign-off required before first pass, supplemental temperature monitoring for cold-weather work, etc. If the WPS preheat requirement was wrong and needs revision, say so.

Disposition. Weld removed and repaired per repair WPS number ___; NDE method and acceptance criterion; post-repair NDE result; CWI sign-off and date.

See: Weld nonconformance report documentation under AWS D1.1

Low-hydrogen practice as the first corrective action

For the large majority of weld cracks in structural fabrication — particularly on steels with carbon equivalents above 0.40 — hydrogen is either the cause or a contributing factor. The most effective single corrective action is verifying low-hydrogen practice before the repair weld:

Confirm the electrode hydrogen designator: for SMAW, E7018-H4R, E7018-H8, or E7016-H4R are specified for the common structural grades where HIC is a risk. E7018 without an H-designator has no guaranteed hydrogen limit.
Confirm electrode storage and conditioning: E7018 out of an unopened hermetic container is acceptable for immediate use; reconditioned electrodes from a rod oven held at 250–300°F are acceptable; electrodes left on an open bench overnight are not.
Confirm preheat before the repair weld: measure at the required distance from the joint per the WPS, not at a convenient surface location.
Consider increasing the preheat for the repair if the original preheat was marginal and the ambient temperature is low.

See: Low-hydrogen electrode storage and conditioning: H4 through H16

Pattern cracking: when a single repair is not enough

A single crack on a single joint may be an isolated quality failure — one welder, one cold morning, one missed preheat check. But when the same type of crack appears on multiple joints in the same week, on the same heat of base metal, or on the same welder's work, the investigation must escalate beyond the individual NCR to a systemic review.

Pattern cracking requires examining whether:

The base metal heat (MTR carbon equivalent) is consistent with what the WPS was qualified on
Preheat verification practice is consistent across the crew or has gaps in cold weather
Electrode handling practice has changed (new supplier, storage location, or oven behavior)
A joint detail change — deeper groove, tighter root opening, thicker section — has increased restraint beyond what the existing WPS was qualified to handle

The corrective action for pattern cracking typically involves the WPS: either the preheat is increased, the filler metal hydrogen designator is tightened, or the procedure is requalified for the actual base metal and joint geometry in production.

Closing the loop

Every crack investigation should end with a closed NCR that includes: cause, corrective action, post-repair NDE acceptance, and CWI sign-off. Open NCRs at the time of final inspection are a red flag for the AHJ, owner's inspector, or certifying body. If the corrective action cannot be completed before the final inspection — for example, the cause is still under metallurgical investigation — the NCR should be escalated to the engineering of record before the structure is placed in service.

Keeping weld crack investigations, repair records, and NCRs linked to the original WPS and welder qualification in the same project file makes final inspection and certification package assembly straightforward. WPS Welding connects the procedure library, inspection records, and welder qualifications so the audit trail is always complete.

Rule library based on AWS D1.1:2025; verify against your governing edition.