Purchaser Specification, Code, and Shop Procedure Disagree
The contract drawing invokes ASME Section V Article 7 and ASTM E709 for magnetic particle testing, with acceptance per the purchaser's specification. The purchaser's specification requires wet fluorescent MT, black light of at least 1000 uW/cm2, and residual field of 3 G maximum after inspection. Your company procedure, written to a superseded revision of E709, allows dry powder for vertical and overhead surfaces and says nothing about residual field measurement. On site, the subcontractor used dry powder on the vertical welds and did not demagnetize anything. The purchaser's inspector has placed a hold. The subcontractor argues that dry powder is 'allowed by the code' and that demagnetization is only required 'when specified'.
1. Resolve the document conflict. Which requirement governs and what happens to the affected welds?
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Establish the hierarchy before arguing about technical merit: contract and purchaser specification first, then the code invoked (ASME Section V Article 7), then the referenced standard (ASTM E709), then the company or subcontractor procedure. A lower-tier document can never relax a higher-tier requirement, and where two requirements overlap, the more stringent one governs.
Applying that here: Article 7 and E709 permit dry powder as a method in general, but the purchaser's specification has narrowed the permitted method to wet fluorescent. The subcontractor's 'allowed by the code' argument answers a question nobody asked. Likewise, the specification states the residual field limit as a requirement, so the 'when specified' escape clause in the procedure is irrelevant, and the procedure's silence on residual field is a defect in the procedure, not a permission.
The affected vertical welds were inspected by a method not permitted by the contract and without the required demagnetization verification. They are not accepted and must be re-inspected by wet fluorescent MT to the specified technique, with residual field measured and recorded. Raise a nonconformance report, hold shipment, and notify the purchaser's inspector in writing.
2. What must be done to your company procedure before work resumes, and is a demonstration required?
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Revise and re-approve, not just annotate:
- Align the method with the purchaser's specification: wet fluorescent as the default for all surfaces, dry powder only if the purchaser grants a written deviation.
- Update the referenced E709 revision and confirm nothing else in the procedure depended on the superseded text.
- Add the residual field requirement with the measurement method (instrument, three orientations, acceptance value), the demagnetization method, and the record to be kept.
- Add the black light minimum of 1000 uW/cm2 and the ambient light limit for fluorescent work.
- Route the revision through the same approval chain as the original, including the purchaser or authorized inspector, before any production inspection.
Demonstration: any change that affects detectability requires evidence. Run the revised technique on a reference specimen or a production weld with known indications and show that the specified indications are found with the specified particle, light level, and field. Record the demonstration. A procedure revision approved on paper only, with no capability evidence, will not survive an audit and does not protect the welds already accepted under the old revision.
3. The subcontractor offers to 'prove equivalence' by showing dry powder finds the same cracks. How do you handle that offer?
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Treat it as a formal deviation request, not a field experiment.
The technical reality is that dry powder and wet fluorescent are not equivalent for this application. Wet fluorescent gives higher contrast under UV with controlled ambient light and is generally more sensitive to fine, tight surface cracks on smooth, ground or machined surfaces, which is what a ground flush weld presents. Dry powder is convenient for portable work, rough surfaces, and elevated temperature, and its particles are generally coarser. An equivalence test might show both find a large crack and still show the wet method finding finer ones, so the offer may well fail.
Process: the subcontractor submits a written deviation request with a test plan to the purchaser for approval before any inspection credit is claimed. The plan must use a specimen or welds with characterized indications spanning the size range of concern, defined acceptance, and independent witnessing. The purchaser, not the subcontractor, decides whether the demonstration is adequate. Until written approval exists, the specified method stands and the welds are re-inspected wet fluorescent. Record the whole exchange in the project quality file.