4 replies to this topic

[NOPE.AVI]

Howdy y'all,

I am running in to a problem that seems to be dodged every where I look. At my facility there are two vessels with ASME stamped plates that give a design pressure of "atmospheric". There is now maximum allowable working pressure (MAWP) stated in any documentation I can find. These tanks have nitrogen pads attached to them making for inert atmospheres. These vessels already have pressure safety valves attached. Since some important engineering documentation has been lost, it has been my job to recollect this information and check that these valves are adequately sized.

My question is this. How can I find a set pressure appropriate for a vessel like this? I brought this issue up with my supervisors and they are getting the tanks inspected to determine the MAWPs. I am looking for an answer that could help me in the immediate future, just to get a feel for sizing equations, or later on in my career if I run into this problem again. I plan on using this input to help with my initial assessment of how this valve has been sized.

I'm sure there are plenty of engineers that pull there hair out over this, and I want to save some scalps. Thank you so much for your time.

Supplemental information:
The existing pressure relief valve has a set point of 3"H2O and a vacuum relief set pressure of -0.865"H2O.
Nitrogen pads are set to keep an atmosphere between 0.5"H2O and 2"H2O.
These vessels are storage vessels.
This facility is a biodiesel plant.

Sincerely,



Nope.avi

[fallah]

Hi,

IMO, as you mentioned, let the tanks to be inspected in order to determine the present MAWP/MAWV.Then nitrogen pad, pressure/vacuum relief, emergency relief settings would be arranged to be specified/evaluated as per two mentioned values.

Fallah

[Steve Hall]

You could also contact the tank manufacturer. Nameplate data should include a serial number.

[kkala]

Based on the set points of pressure relieve vent and pressure vacuum vent, understanding concerning the design pressure / MAWP of mentioned atmospheric tanks is : overpressure = + 3 in H2O g = 76 mm H2O g, vacuum = - 0.865 in H2O = - 22 mm H2O g. This under the assumption that the tank vendor has also installed the mentioned vents, which is possible. At any case tank Vendor should be consulted.
See http://www.cheresour...esign-pressure/ '> http://www.cheresour...esign-pressure/ for atmospheric tanks.
Mentioned design pressures cannot be excluded (http://www.tycoflowc...cm106-13900.pdf '> http://www.tycoflowc...cm106-13900.pdf , Tank Protection), yet typical design limits of atmospheric tanks are +560 mm H2O g and - 60 mm H2O g (see first web reference above). Probably I miss something, even though tank set points of release vents may have some margin over actual tank design pressures (max / min). Advice on this point would be appreciated, subject is under question from my side.

[Art Montemayor]

Nope.avi:

This is a serious issue and has been battered around since the Forums were started. I won't rant and rave anymore, but you can refer to the following thread and the implied solution to your problem:

http://www.cheresour...mawp#entry57162