Weeping Crack in a Firetube Boiler Shell Weld
During an internal inspection of a 30,000 lb/hr, 150-psig firetube boiler, the authorized inspector finds a 3-inch longitudinal crack in the shell-to-tube sheet weld at the rear turn-around. The crack is visible with the naked eye, and a small amount of water seeps from it after the boiler is filled for hydro. The boiler has no prior repair records and is inspected under NBIC Part 2 for inservice service. The owner says the boiler must remain online for six more months because the plant has no backup steam. Operating pressure is 125 psig; the safety valve is set at 150 psig and was tested last year. The inspector must decide whether the boiler can be returned to service, what immediate actions are needed, and what repair documentation would be required. The jurisdiction requires NBIC repairs and R-stamp work.
1. What does the crack indicate, and can the boiler be returned to service as-is? Explain the code and safety reasoning.
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The crack is a pressure-retaining weld defect, not a cosmetic leak. Weeping during hydro means the crack is at least through the inner surface and may be through-wall; a crack in a boiler shell or tube sheet weld is not acceptable for continued service under NBIC Part 2 without repair or an engineered fitness-for-service evaluation. The boiler should be removed from service, depressurized, drained, and tagged out. The jurisdiction should be notified because the repair will be Code work. I would not accept the owner's six-month delay based on operating pressure being below MAWP: lower pressure reduces stress but does not stop crack growth or guarantee ligament strength. Return to service requires an R-stamp repair by a qualified organization, an approved repair procedure, crack removal or excavation, NDE to confirm extent, and hydrotest. The inspector's role is to verify the repair scope and records, not to authorize operation with a known crack.
2. If the owner insists on postponing repair, what interim measures, if any, are defensible, and who must approve them?
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If the owner requests interim operation, I would require a written engineering evaluation by the R-stamp holder or an engineer experienced in boiler fitness-for-service, plus jurisdiction approval. Measures could include lowering the maximum allowable operating pressure, adding monitors, and shortening the inspection interval, but these are not a substitute for repair if the crack is through-wall or growing. I would not approve a clamp or weld overlay without a Code repair procedure and NDE. The inspector should document the crack location, length, depth indication, and leak rate, and state that continued service is outside the inspector's authority if the jurisdiction has not accepted it. In practice, the defensible answer is shutdown and repair; any interim operation is an owner and jurisdiction risk decision, not an inspector's unilateral approval.
3. Outline the repair path: stamp, procedure, NDE, hydro, and records.
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Repair path: select an R-stamp holder; remove the crack by grinding or excavation, confirm removal with MT or PT, and evaluate remaining thickness; prepare a repair procedure and WPS/PQR and qualify welders; weld repair per NBIC Part 3 and the original construction code; perform NDE required by the procedure and Code, likely MT or PT and possibly RT or UT; hydrotest at the required test pressure; complete Form R-1 and attach NDE, heat-treatment, and test records; and stamp the R-1 and nameplate as required. The inspector reviews the R-1, verifies the stamp, and confirms that the repair scope matches the records before return to service.