Deferring a Reboiler Inspection and Documenting the Decision
An inspection of a depropanizer reboiler is due in 3 months, but the next unit turnaround is 14 months away. The last RBI assessment ranked the item as medium-high risk, driven by external chloride stress corrosion cracking under insulation. A contractor's verbal comment said 'the paint looks fine.' The unit has had one small pinhole leak on a similar reboiler 2 years ago. The operations manager wants to defer to the turnaround and asks the inspector to sign off on the deferral.
1. What information and justification are needed before any deferral can be considered?
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A verbal 'paint looks fine' is not adequate. The deferral package should include the current RBI assessment, the credible damage mechanism, inspection and leak history (including the similar reboiler pinhole), consequence of failure, and the proposed duration. It should explain why the external chloride stress corrosion cracking risk has not increased and what interim measures will control it.
The justification must address uncertainty: the reboiler has not had an effective inspection for the suspect mechanism, and visual paint condition does not detect under-insulation cracking. The deferral should be processed through the site's management-of-change or risk-acceptance procedure, not granted as an informal schedule favor. If the risk cannot be shown acceptable for 14 months, deferral should be refused.
2. Who should approve the deferral, and what records must be updated?
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Approval should come from the responsible inspection or engineering authority, with review by the RBI team and operations. The inspector should not sign off alone under pressure from the operations manager; the decision requires the authority accountable for mechanical integrity and risk acceptance.
Records to update include the RBI assessment and its assumptions, the inspection plan and next-due date, the deferral justification and approval, any interim inspection results, and the management-of-change record. The documentation should state the basis for the extended interval and the conditions that would void it, such as a process change, leak, or insulation damage. This keeps the reassessment and recordkeeping trail defensible.
3. If deferral is approved, what other risk mitigation could support it?
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Supporting mitigation should target the actual mechanism, external chloride stress corrosion cracking under insulation. Options include removing insulation and coating at selected suspect areas, installing insulation plugs or inspection ports, performing remote visual or targeted non-destructive examination at welds and low points, and controlling external water ingress or chloride contamination.
Operations can also reduce risk by controlling the operating envelope and avoiding thermal cycling or wetting cycles that promote cracking. These measures do not replace an effective inspection, but they can reduce the likelihood of an undetected failure during the deferral period. Each measure should have an owner, completion date, and documented acceptance in the deferral record.