Clarification for MAWP of the Vessel

The client is requested to define exactly the MAWP (not design pressure) at vessel datasheet, and from which you can easily find the design pressure of each component of vessel, and also you can easily find the hydrostatic test pressure as specified by the design code.

See CR4 Thread: Governing MAWP - Nozzle Pad.ode

Thanks Sir Abdel Halim & Sir Tornado

There may be a confusion between the design pressure of the process system and the design pressure(s) for a vessel to be used in the system.

For example, I work in ammonia refrigeration. For the refrigeration system, we might design for, say, a condensing pressure of 180 psig under normal operation. With start-up or higher ambient temperatures, there might be excursions to 210 psig. The vessels could be designed for this 210 pressure, but a common standard for ammonia high side vessels is 250 psig MAWP (maximum allowable working pressure).

If the vessel is tall and contains liquid, the pressure near the bottom will (because of liquid head) be still higher than the 250 MAWP. Thus some parts of the vessel may need to have a design pressure of perhaps 255 or 260 psig.

Thus it is possible for the design pressure of part of a vessel to be substantially higher then the design pressure of the system where it is employed.