Chris,
I fully agree with you, that`was the reason i was trying to get answer from the
original question poser. since if you specify such high design (1.5 times of
operating)pressure, it would be very large thick walled pipe or vessel. It is
problem usually when operating pressure are very high i.e. such as upstream of
choke valves, etc.
Design pressure are normally determined to have a safe and sufficient margin above the operating pressure.Now this margin could be 10%, 15%, 30% or any other appropriate value per applicable scenario. Design pressure be approached during start up/shutdown/upset/failure, etc. If pressure in the system may exceed above design due to any reason, system need to be protected by means of relieving device for e.g pressure relieve. In case of large inventory may be blow down valve (ESD sytstem) : Good reference could be API RP 521.
However all codes normally give allowance/variation for short time/period provided rest of condition as specified are met. Again point to note is that these variation may not be allowed in category "M"fluid/toxic fluid.
Test Pressure (Hydrostatic Pressure)
recent edition of ASME Boiler and pressure vessel code derated hydrotest
pressure from 1.5 to 1.3, more inline with european code.
regards
alok dubey
On Jul 25, 2007, at 3:40 PM, Alok Dubey wrote:
> My question intent was to understand the logic behind initial
> statement posted quoting Desgin pressure =1.5 * Operating Pressure.
Here's two guesses emphasizing the need for caution in throwing terms
around
1. The original poster cited some sort of company standard. Could be
that the MAWP is
supposed to be 1.5xthe expected normal service pressure to give
some wiggle
room for thermal stress and abnormal service conditions
2. Someone got confused over the terminology and assumed that the
test pressure is a design condition because it's the largest pressure
the vessel ever sees short of an accident.
The third possibility is that no one knew what they were talking about.
Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw@skypoint. com | this distance" (last words of Gen.
............ ......... ......... ......... | John Sedgwick, Spotsylvania
1864)
http://www.skypoint .com/~chrisw/
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[Non-text portions of this message have been removed] Received on Thu Jul 26 01:35:00 2007
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