Hydrostatic Test Decision on a Repaired Shell Nozzle
A small vertical firetube boiler (150 psig MAWP) has a corroded 2-inch shell nozzle that was cut out and replaced by a code-qualified welder. The repair was made with a full-penetration weld, and the welder's procedure and qualifications are on file. The authorized inspector has reviewed the repair and asks whether a hydrostatic test is required before the boiler is returned to service. The boiler was drained for the repair and the safety valve was removed and will be reinstalled. The plant wants to return the boiler to service tonight to meet production. The inspector notes the repair was in a knock-out area and the weld was visually inspected and passed dye penetrant examination.
1. Should a hydrostatic test be performed, and what factors drive that decision?
Read the worked answer
The decision turns on code and jurisdictional requirements for the specific repair, not on production pressure.
Key factors:
- Type and location of the repair: replacing a shell nozzle with a full-penetration weld in a pressure-retaining boundary is a significant repair. Many codes and jurisdictions require a hydrostatic test after repairs to pressure parts, especially where the repair affects the shell or a nozzle.
- Whether the repair is a 'repair' vs. 'alteration' under the applicable code; alterations generally require a hydrostatic test.
- The authorized inspector's judgment and the jurisdiction's rules - the inspector's concurrence is required, and the AHJ may mandate a test.
- NDE performed: dye penetrant on the weld is helpful but does not substitute for a pressure test where one is required.
The plant's desire to return to service tonight does not override the code. If the code or jurisdiction requires a hydrostatic test, it must be done.
2. If a hydrostatic test is required, describe how it should be conducted and what must be verified before firing.
Read the worked answer
Conduct the test per the applicable code:
- Reinstall and secure all openings; the safety valve is typically removed and the opening blanked for the test (or the valve is isolated per code), since the test pressure exceeds the valve setpoint.
- Fill with water (treated or clean) and vent air completely.
- Pressurize slowly to the code-required test pressure (commonly 1.5 times the MAWP for a new or altered boiler, adjusted for temperature per code; confirm the exact factor and any temperature correction with the code and inspector).
- Hold and inspect all welds, the repaired nozzle, and the shell for leaks, weeping, or distortion.
- Depressurize slowly and drain as required.
Before firing:
- Reinstall the safety valve and confirm it is set, sealed, and functional.
- Confirm the inspector's acceptance and that all test records are signed.
- Verify water level, feedwater, and controls are restored; the boiler is not to be fired until the test is accepted and the valve is back in place.