What is Design Pressure and MAWP

By Samiran

Maximum Allowable Working Pressure (MAWP) is always equal to, or higher than the Design Pressure (DP). The DP is normally the Pressure Relief Valve’s (PRV)) set pressure of a vessel. The DP is used to determine the minimum wall thickness. Say a calculated thickness is 9.2 mm based on a desired pressure. However, a standard material may have a thickness of 10 mm. If the pressure is now back calculated based on this thickness, this will be the MAWP.

In my experience, the vessel designer/fabricator will not back-calculate the MAWP based on actual thickness automatically. They will if they are asked to, but not normally. So, I’d say it’s up to the Engineer specifying the vessel to make this happen.

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I would agree with Latexman - and i think that “definition” of MAWP is a little dangerous since often the weakest link in any piping/equipment configuration is the nozzles/flanges that then may be weaker than MAWP - and that doesn’t make sense?

I thought that MAWP and design pressure was the same and that the term MAWP came from ASME and engineers from other countries than the US (such as myself) more often used design pressure but meaning the same=the set point of your PSV?



MAWP is equal to DP when the calculations that Latexman is referring to are not completed.
See MAWP Definition: App. 3-2