Adding a Nozzle to a PWHT Air Receiver
An owner wants to add a 2 in. NPS 80 nozzle to the top of a horizontal Section VIII Div. 1 air receiver built in 2005. The shell is 1.25 in. SA-516 Gr 70, MAWP 200 psig at 150°F, MDMT 20°F, and the original U-1A lists postweld heat treatment because the purchaser specified it for caustic service. The vessel is in a process area; the owner's maintenance crew proposes to cut the opening, weld a SA-106 Gr B nozzle with a full-penetration groove plus fillet, and hydrotest at 300 psig. The R-stamp holder's procedure says PWHT is not required because UCS-56 requires it only above 1.5 in. nominal thickness, and the new groove is about 0.5 in. deep. The owner wants the work done during a 48-hour shutdown. The AI is asked to review the package.
1. Is adding the nozzle a repair or an alteration, and who may perform the work?
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It is an alteration, not a routine repair. Adding a nozzle changes the pressure-containing geometry and requires a design check for opening reinforcement, nozzle neck thickness, weld size, and any effect on the vessel's pressure rating. Under NBIC, the work must be performed by an R-symbol holder authorized for the scope, with an Authorized Inspector reviewing the design, procedure, and completion. The owner's maintenance crew cannot perform this work merely because the vessel is theirs. Before welding, the AI should review the original U-1A and drawings, confirm the shell material and thickness, verify the opening reinforcement calculation per UG-37 and the nozzle attachment details, and confirm that the R-stamp holder's quality program covers the work. The AI should also verify that the proposed 300 psig hydrostatic test is not automatically acceptable: Section VIII hydrotest is normally 1.3 times MAWP, or 260 psig here, and a higher pressure requires justification under the original code and design.
2. The R-stamp holder argues that PWHT is not required because UCS-56 triggers at 1.5 in. and the new groove is only about 0.5 in. deep. Evaluate that position.
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The argument is incomplete and should not be accepted as stated. UCS-56 thickness limits are one route to PWHT, but they do not override a PWHT requirement imposed by the original construction or by the service. The original U-1A lists PWHT for caustic service. Caustic service is associated with stress-corrosion cracking, and the original PWHT was presumably required to reduce residual stresses. An alteration that introduces new weld residual stresses in the same pressure boundary should maintain the original requirement unless a qualified engineering evaluation, accepted by the AI, shows that PWHT can be omitted without compromising the vessel. The R-stamp holder must use a PWHT procedure with documented heating and cooling rates, temperature control, and thermocouple placement, and must perform required NDE after PWHT. The AI should not approve the alteration package on the basis of the 0.5 in. groove depth alone.
3. What NDE and documentation should the AI require before signing the alteration report?
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The AI should require NDE appropriate to the joint and the original vessel requirements. At minimum, the nozzle-to-shell groove weld should receive PT or MT on the root and final passes, and the finished weld should be examined by the method specified in the R-stamp holder's procedure. If the original vessel was radiographed, the AI should determine whether the new weld is required to receive RT or UT; nozzle attachment welds are often examined by surface methods, but the alteration procedure must state the basis. After PWHT, the same surface examination should be repeated as required. The AI should also require: the design calculation and sketch; the WPS/PQR and welder qualifications; the PWHT chart; the hydrostatic test at the Code-correct pressure, witnessed by the AI; and a completed NBIC alteration report signed by the R-stamp holder and the AI. The owner's 48-hour schedule does not justify skipping PWHT, NDE, or the witnessed hydrotest.