Scope Decision for a Pressure Vessel in a Mixed-Service Unit
An owner operates a hydrocracking unit with a 4.2 m diameter, 18 m tall carbon-steel reactor that has been in service 22 years. During a turnaround the inspector finds a 40 mm long, 3 mm deep surface-breaking crack in a longitudinal weld on the shell. The owner's engineering group wants to perform an in-house fitness-for-service assessment and return the vessel to service without notifying the certifying body that holds the vessel's registration. The vessel is stamped and registered under a certification program. The unit is in a jurisdiction that mandates third-party inspection of pressure equipment. The owner asks the API ICP inspector on staff whether they can simply document the crack in the maintenance log and proceed.
1. What should the inspector consider before agreeing to the in-house path, and what is the correct course of action?
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The inspector must separate three questions: (1) Is the vessel within the scope of a certification program? Yes - it is stamped and registered, so the applicable code's requirements for alterations, repairs, and fitness-for-service still bind the owner. (2) Does the jurisdiction impose additional third-party inspection? The setup says yes, so the local inspector's authority is independent of the owner's preference. (3) Is an in-house FFS acceptable?
An FFS assessment may be permitted by the applicable standard, but it must be performed by qualified personnel using an accepted methodology, and any repair or alteration affecting the pressure boundary typically requires involvement of the authorized inspector and the certifying body before return to service. Documenting a pressure-boundary crack only in a maintenance log, with no authorized-inspector review and no notification, is not defensible.
The correct action: flag the crack to the authorized inspector, ensure the FFS is performed and reviewed per the applicable standard, obtain the required approvals before returning to service, and record the disposition. The inspector does not have authority to waive code or jurisdictional requirements on the owner's behalf.
2. The owner argues the crack is 'only 3 mm' and below any concern threshold. How should the inspector frame the response?
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Depth alone is not a disposition criterion. The inspector should point out that acceptability depends on the applicable assessment method, the material toughness, the stress state at the weld, and the inspection method's detection limits - not on an informal '3 mm is small' rule.
A defensible response: (a) confirm the crack is fully characterized (length, depth, orientation, proximity to other flaws) with an appropriate NDE method; (b) require a documented FFS per the applicable standard; (c) confirm the material's toughness assumptions are valid for 22 years of service (possible embrittlement, hydrogen, or temper embrittlement in a hydrocracker); (d) set a re-inspection interval if the flaw is accepted. The inspector's job is to insist on the process, not to substitute a rule of thumb.