Replacing a Small Drain With a Larger Flanged Nozzle
A plant has a 48-inch-diameter, 200-psig horizontal pressure vessel, SA-516 Gr. 70, built to ASME Section VIII Div. 1 in 2005. The vessel has a 2-inch threaded drain at the bottom. The owner wants to replace it with a 4-inch flanged nozzle and add a 1/4-inch reinforcing pad because the new piping requires a larger connection. The contractor holds an R stamp but not an S stamp. The vessel is insulated and in service; the owner plans to take it out of service for the work. The inspector is asked whether this is a repair or an alteration, what design and documentation are required, and whether the contractor can do the work. The jurisdiction enforces NBIC Part 3.
1. Is this a repair or an alteration? Explain.
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This is an alteration, not a repair. A repair restores a vessel to its original design; this change replaces a 2-in opening with a 4-in opening, adds a reinforcing pad, and changes the nozzle configuration and piping loads. Under NBIC Part 3, that is an alteration because it changes the design or pressure-retaining configuration. The contractor's R stamp is necessary but not sufficient by itself; the holder must be qualified for alterations and must work under the jurisdiction's requirements. The owner needs an engineering design for the new nozzle, including reinforcement per UG-37, weld details, and load analysis. The inspector should not treat this as routine maintenance or a field fit-up.
2. What design, welding, NDE, and testing requirements apply?
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Design requirements include calculating required reinforcement for the 4-in opening, considering the pad and any compensation; checking nozzle neck thickness and flange rating; evaluating external loads from piping; preparing a WPS/PQR and qualifying welders; and using material identification and proper preheat if required. NDE should follow the original Code and NBIC Part 3, likely PT or MT on the root and final weld and RT or UT if the joint is a butt weld. Hydrotest at 1.3 times MAWP or the Code-required test pressure after completion, unless the jurisdiction accepts an alternative. The reinforcing pad needs a tell-tale hole or vent as required. PWHT may be required depending on thickness and material; that must be decided in the design.
3. What records and stamping are required, and what is the inspector's role?
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Records include an R-2 alteration report, design calculations, drawing, WPS/PQR, welder qualifications, NDE reports, heat-treatment records if applicable, hydrotest record, and nameplate update or supplemental nameplate as required. The R-stamp holder certifies the alteration and stamps the report. The inspector reviews the package before return to service, verifies the stamp and scope, and confirms the jurisdiction has been notified or has approved the work. The inspector does not design the alteration; the inspector verifies that the design and work meet the Code and that records are complete.