Superheater Header Replacement with Incomplete Section I Documentation
A 1958-vintage 150 MW reheat boiler is in a 21-day outage to replace the secondary superheater outlet header after repeated ligament cracking. The owner’s engineer proposes to field-fabricate the header from SA-335 P22 pipe and weld it to the existing outlet steam line. The OEM drawing is marked “for reference only,” and the replacement material test reports list heat numbers but no ASME Section I partial data report. The authorized inspector has not been invited to the pre-weld meeting. The contractor says post-weld heat treatment is unnecessary because the wall is “only 28 mm” and proposes 10% radiographic examination of the circumferential weld. The unit must return before a capacity auction, so operations wants to hydrotest immediately after welding. The jurisdiction has adopted ASME Section I and the NBIC. The plant’s last Section I inspection found the safety valve data reports acceptable, but the owner has no written repair procedure for P-No. 5 material.
1. Before the old header is cut out, what code basis, documentation, and acceptance authority must be settled? Be specific about the Section I part data and the inspector’s role.
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The header is a Section I pressure part, so the replacement cannot be treated as a generic piping spool. I would require: (1) a design basis signed by the original boiler manufacturer or a qualified engineer showing the header meets Section I rules for pressure, temperature, and ligament efficiency; (2) material test reports traceable to the heat numbers with chemistry, tensile, and impact results for SA-335 P22; (3) a Section I Manufacturer’s Data Report for the part (Form P-2) from a holder of the appropriate ASME Certificate of Authorization, not just mill certificates; (4) a repair/alteration procedure accepted by the authorized inspector under the NBIC, including the weld procedure specification and procedure qualification record per Section IX; and (5) a written hold-point plan agreed with the inspector. The authorized inspector, not the contractor or operations, holds acceptance authority for code compliance. Without P-2 and traceability, the part is unapproved regardless of the auction date; the correct decision is to stop cutting until the documentation is closed.
2. Assess the contractor’s two technical proposals: no PWHT at 28 mm and 10% RT. What would you approve and what would you reject?
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Reject both as proposed. P22 is a P-No. 5A creep-strength steel; at 28 mm the Section I/NBIC PWHT exemption is not available, and “only 28 mm” reverses the logic-thicker sections need PWHT, not less. PWHT is needed to temper the martensitic/bainitic heat-affected zone, reduce hardness, and restore creep ductility. The contractor must provide a PWHT procedure with thermocouple placement, heating/cooling rates, hold temperature and time, and a hardness survey; the inspector should witness or review the chart. For NDE, 10% RT is not a Section I acceptance basis for this circumferential pressure weld. I would require the Code-required volumetric examination (normally full radiography, or an approved alternative only if the Code and inspector permit it) plus surface examination of the root and cap, and PT/MT as applicable. The weld procedure and welders must be qualified per Section IX for P-No. 5A. If the contractor cannot meet these, the work should be re-planned, not accepted by concession.
3. Operations wants to hydrotest immediately after welding and return to service. Give the sequence you would enforce from weld completion to reheat, including the inspector’s hold points.
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The sequence is: complete welding with documented WPS/PQR and welder qualifications; perform root and final NDE as required, with the inspector holding the weld before PWHT; complete PWHT and verify the chart and hardness; perform final NDE after PWHT because PWHT can open defects; then hydrostatic test at the Section I test pressure (1.5 × MAWP, adjusted for temperature) with the inspector present; inspect for leakage and permanent deformation; complete the NBIC repair record and P-2 data report; reset and test safety valves per Section I; then controlled warm-up and reheat. Immediate hydrotest after welding is wrong because untempered weld metal and HAZ may pass a hydro and still fail in creep service; it also misses the post-PWHT NDE. The inspector’s hold points are after weld completion, after PWHT, and at hydro. If the auction window cannot accommodate this, the honest answer is to delay return, not to compress the code sequence.