MAP & MAWP

[E9]

Hi !!

Can some one please tell me the real logic why MAP & MAWP are always calculated at the top of the vessel???

 

[JoeTank]

It provides a means to establish a uniform definition for MAWP. It would seem that any other spot would be adequate also (ie; at the bottom of a vessel) as long as it is uniformly applied. By using the top of the vessel it is absolutly clear that it is a pressure applied from an external source.

Joe Tank

 

[E9]

but by definition MAWP is the pressure calculated minus the static head means it should always be taken at the top of the vessel ?? and quote

"By using the top of the vessel it is absolutly clear that it is a pressure applied from an external source."

creates some confusion because as far as i know it is the pressure calculated against the actual governing pressure and is used for re rating the vessel .. Please could u elaborate these two points.

BR

 

[JoeTank]

In ASME VIII the MAWP at the top of the vessel is stamped on the nameplate. The design pressure, P for a given part is the MAWP of the vessel plus any static head for that part. The MAWP shown on the nameplate may be one of two things. The first option is the easiest... just use the MAWP for the vessel as stated by the owner. The second option is to calculate the MAWP for a vessel part (as-designed minus corrosion allowance, if any) and deduct the static head. The MAWP for the vessel is then taken as the lowest MAWP for each part (adjusted for static head for each part). It's a bit confusing at first but after you get your head wrapped around it it atatrts to make sense.

Joe Tank