3 replies to this topic

[yog123]

Does anyone have any idea about what is maximum vessel wall Temperature (Tw) is tp be considered for SA387 grade 11, Class 2 during fire case where vessel is filled with gas?

[Pilesar]

The pressure vessel documentation should identify the Maximum Allowable Working Temperature.

[shvet1]

Does anyone have any idea about what is maximum vessel wall Temperature (Tw) is tp be considered for SA387 grade 11, Class 2 during fire case where vessel is filled with gas?

 

It is hard to answer as firecase is related to overstress of vessel wall as combination of T plus P, not T alone. This fact means that MAWT of wall can be exceeded without vessel disruption if pressure in vessel during firecase is relatively low. Firecase of this kind of vessels is subject to overstress calculation, not P or T alone.

 

The situation is common when an engineer is misleaded by word "pressure" in term "pressure safety valve/device". PSVs are intended to prevent overstress, not ovepressure, as overpressure or overheating alone do not cause vessel/piping disruption.

 

Anyway there is some limit related to creep temperature of metal. In practice if pressure in vessel exposed to flame is not enough to provide overstress regardless to wall temperature - gasket failure temperature most often becomes min limit for firecase. Consult piping engineer for max gasket temperature allowed and compare it with creep temperature of SA387.

 

Note that situation when vessel filled with gas only can not be overstressed during firecase is quite often if design pressure is much higher then operating pressure. In this case pressure safety valve will not prevent vessel failure and therefore max allowable temperature of the weakest element of pressure system exposed to flame to be considered. In most such cases it is a gasket.

 

During overstress modelling keep in mind local overstress caused by overdesign expansion of metal details overheated above MAWT like nozzles, bends.

Edited by shvet1, 15 December 2022 - 03:10 AM.

[snickster]

Tanks and vessels are usually designed to API 520/521/2000 for external fire conditions.  Automatic sprikler systems are use to mitigate occurance of high metal temperature that will cause undue strength decrease of the metal wall.  Alternately insulation or coating systems can be used.

Edited by snickster, 17 December 2022 - 09:36 PM.