MAWP Temp and Pressure
MAWP Temp and Pressure
(OP)
Recently at one of our plants we had a 5 year PHA revalidation. During this PHA the 3rd party facilitator question one of our vessels that operates at 780psig @108F to 115F base on ambient conditions. The name plate on the vessel indicates design condition of 1440psig @ 100F. What should be the right course of action for this vessel, is rerating the vessel to cover the 10 to 20 degree difference in temperature required? the relief valve on this vessel is set to 950psig.





RE: MAWP Temp and Pressure
RE: MAWP Temp and Pressure
Now for the assumption, since this was not clearly stated in the original post: Let's presume that this is a VIII Div. 1 vessel. I'll also presume that the vessel is not insulated.
Keep in mind that the design temperature for a Div. 1 vessel is the average thru-wall temperature of the steel. [Note that this is not the case with all codes, e.g. B31.3.] Thus, depending on circumstances you may find that you can measure the outside metal temperature of the vessel (after sun exposure on a hot day), assume that the inside surface metal temperature is the same as that measured for the process fluid, and average the two. In some parts of the world this will make things worse, in others it will make them better.