NDT found a defect. What happens next?

1. Read the report properly

An indication is a response from the inspection method. It becomes a defect only when it exceeds the acceptance criteria of the standard the weld was made to. A good report makes that call for each indication and shows how it was reached.

Before planning anything, check that the report states:

• the method and technique used, and who performed it
• the standard and acceptance criteria applied, including the weld category
• each indication's location, type and size as found
• an accept or reject call for each weld, with the location and extent of any defect

If the acceptance criteria or the weld category are wrong, every call after them is wrong too. For structural steel welded to AS/NZS 1554.1, for example, the acceptance levels differ between GP and SP welds.

2. Fabrication defect or in-service crack?

These need different thinking. A fabrication defect found before service, such as lack of fusion or a slag inclusion, usually comes from technique, access or the procedure's parameters. Repair it to a prequalified or qualified procedure and re-inspect, and if the same defect keeps appearing, fix the cause before more welds are made.

A crack found in service is different. Something is driving it, very often fatigue, and repairing the crack without dealing with the cause tends to put the same crack back in the same place. If the component has cracked before, treat it as a failure investigation, not just a repair.

3. Choose the pathway

There are four realistic options for a rejected indication:

• Repair to the original standard. Excavate, confirm removal, re-weld to a qualified procedure and re-inspect. This is the most common outcome.
• Engineering assessment. AS/NZS 1554.1 provides for imperfections beyond its tabulated limits to be accepted on the basis of a fracture mechanics assessment, with the principal's agreement. That is an engineering exercise with its own evidence, not a shortcut.
• Monitor. For some in-service indications on lower-criticality components, a documented monitoring plan can be defensible, provided an engineering assessment sets the inspection interval and the size at which repair becomes mandatory. The decision and its reasoning must be written down. Monitoring is not a way to accept a rejected weld in new fabrication.
• Replace. When the damage is extensive, when repairs keep failing at the same place, or when the design detail itself is the problem.

Criticality should drive the choice. A crack in a bracket and a crack in a boom foot are not the same decision.

4. What a weld repair procedure contains

"Grind it out and weld it up" is an instruction, not a procedure. A weld repair procedure should cover:

1. Identification. The indication, its location and its size as reported.
2. Excavation. The method (grinding, or air-arc gouging followed by grinding back to clean metal), any preheat the material needs before gouging, an excavation profile the welder can fuse into, and the requirement to follow a crack to its full extent or to dig out a buried defect until its removal is confirmed.
3. Confirmation of removal. Magnetic particle or penetrant testing of the excavation before any welding starts.
4. The welding procedure. A prequalified or qualified WPS that covers the repair as excavated: its shape and depth, the material, the thickness and the position. An excavation often does not match a prequalified joint preparation, so check the fit before relying on the prequalified route. Where it does not fit, the repair procedure needs qualifying by another route.
5. Preheat and interrun temperature. Determined for the repair itself: the material, the combined thickness at the repair, and the arc energy and hydrogen control of the repair runs. Do not carry it over from the original WPS or a different job. For quenched and tempered steels, the upper limits on preheat, interrun temperature and arc energy matter as much as the minimums. Repairs are often more restrained than the original weld, which raises the cracking risk.
6. Sequence. A welding sequence that controls distortion and residual stress.
7. Finishing. Dressing or grinding where the detail is fatigue sensitive.
8. Re-inspection. The method (at least the method that found the original defect), the extent and the acceptance criteria and, where the material and thickness call for it, a delay before final inspection to allow for delayed cracking.
9. Records. Who did what, to which procedure, with which results.

5. Put hold points where they matter

Two points in a repair deserve a hold: before welding, to confirm the excavation is clean and the defect is gone, and after re-inspection, to release the component. Put them on an Inspection and Test Plan with a named person to release each one.

6. Make the repairs visible in your CMMS

A reject that lives only in a PDF gets forgotten. Each repair should become a work order with the procedure attached, the hold points as operations, and the re-inspection as its own step. That also builds the history you will need the next time the same component cracks.

7. Decide whether the repair needs certification

If a client, site or regulator will rely on the repaired component for structural adequacy, the repair design should be independently reviewed and certified by a registered engineer before it is used. Veristruct prepares the full technical package and coordinates independent review and certification through registered engineering partners.

How Veristruct helps

Veristruct writes weld repair procedures, repair designs and ITPs from NDT reports, and investigates repeat cracking. For teams handling a steady flow of NDT reports, the Veristruct WPS Tool drafts a repair procedure for each rejected indication, marked for review before use.