Three different sets of Temp & Pressure on a Vessel's nameplate.
Three different sets of Temp & Pressure on a Vessel's nameplate.
(OP)
I'm trying to calculate Mean Allowable Wall Thickness (MAWT) of a Flare knock out drum (Design code of construction is ASME VII Division 1 – W82). Peculiarly there are following three sets of design pressure and temperature values stamped on the Vessel's name plate as well as mentioned on its GA drawing.
Case I - 7.4 barg @ -79/90 C
Case II – 5.6 barg @ -79/199 C
Case III – 3.6 barg @ -79/224 C
The problem is if I take the worst case scenario meaning max pressure and temperature value of all three cases i.e. 7.4 barg @ 224 C, the required MAWT comes out to be more than the current nominal wall thickness of the vessel which essentially means it was not fit for service from the day 1. But when I calculate MAWT based on above individual cases separately, the required MAWT in all three cases is less than the nominal wall thickness of the vessel. My questions are
Does ASME VIII code allow that a Vessel's nameplate can have more than one set of temperature and pressure stamped?
Assuming worst case scenario, am I correct here in calculating MAWT based on max: pressure and temperature of all three cases?
Regards,
Schaali
Case I - 7.4 barg @ -79/90 C
Case II – 5.6 barg @ -79/199 C
Case III – 3.6 barg @ -79/224 C
The problem is if I take the worst case scenario meaning max pressure and temperature value of all three cases i.e. 7.4 barg @ 224 C, the required MAWT comes out to be more than the current nominal wall thickness of the vessel which essentially means it was not fit for service from the day 1. But when I calculate MAWT based on above individual cases separately, the required MAWT in all three cases is less than the nominal wall thickness of the vessel. My questions are
Does ASME VIII code allow that a Vessel's nameplate can have more than one set of temperature and pressure stamped?
Assuming worst case scenario, am I correct here in calculating MAWT based on max: pressure and temperature of all three cases?
Regards,
Schaali





RE: Three different sets of Temp & Pressure on a Vessel's nameplate.
RE: Three different sets of Temp & Pressure on a Vessel's nameplate.
Each individual element must be designed for the worst case coincident pressure and temperature per UG-21. This would be one of the three cases you listed, but it might be a different case for each element. In practice, if you're using a cmputer, you just run all your calculations three times.