Repairs, Alterations, and Rerating
Three different things
- Repair: work that restores a vessel to a condition suitable for safe operation at its existing design conditions - weld build-up, replacing a corroded area with like material, sealing a leaking seam. Welding on the pressure boundary is a repair.
- Alteration: a physical change with design implications - adding or enlarging a nozzle, changing material, changing design pressure or temperature, changing geometry. Alterations need design calculations and approval.
- Rerating: a change in MAWP or design temperature based on re-evaluation, calculated to the original code of construction (or another code acceptable to the inspector).
Controls
Welding requires a procedure and welders qualified to ASME Section IX; examination follows Section V; postweld heat treatment and hydrostatic testing are applied as the construction code requires, with API 510 allowing alternative testing under defined conditions. In jurisdictions adopting the National Board Inspection Code, repairs and alterations to pressure-retaining items must be done by an organization holding the appropriate NB symbol (e.g., R), with the work authorized by the authorized inspector. Even without a jurisdiction, the owner/user's API 510 inspector must approve the repair method before work begins and review the completed work.
Documentation
Records must identify the repair, materials, procedures, NDE results, and any rerating calculation; the nameplate must be updated or a rerating tag applied.
Traps
- Calling a nozzle addition a "repair" - it is an alteration.
- Rerating without recalculating required thickness at the new condition.
- Overlooking that raising MAWP generally calls for a hydrostatic test at the new rating.
Rule of thumb
Ask whether the design basis changes. If yes, it is an alteration or rerate; if you are only restoring the original design basis, it is a repair.