Pressure Relief for cryogenic vacuum vessel

[dan240]

Hello,

I have a Cryo Test Bed we use that consists of a ~4 cuft dome evacuated with a small turbo and cooled with an ancient cold-head. There is no LN2 cooling or any other cryogens introduced into the system. (for cooling or otherwise) .

We have a pressure relief valve on the chamber but it does not have a part number and I have no idea where it originally came from. I have been asked to make sure that the pressure relief valve is adequately sized for the system

I am sitting here thinking about how to do that and would appreciate any help. The pressure will be generated by a leak into the vacuum system where it is condensed and then reheated and vaporized on warm up, generating the pressure.

I was going to assume a heat leak into the system and then calculate the amount of air that could be vaporized by that heat to give me the amount of gas that could be generated. Then find a new pressure relief that has some specs so I can determine the pressure drop across the valve and determine what the maximum pressure generated inside the vessel could be.

Sound like the right thing to do?

Best,
Dan

 

[iainuts]

Yes, that's basically the idea. There are very similar situations throughout the industry. For example, cryogenic tanks and piping that are VJ will have RV's on the annular space (ie: the evacutated portion of the tank or line) and on the pressurized portion (ie: inner line or tank), so your situation is not unusual.

In fact, it's so common that the CGA has created guidelines for these situations. You can fall back on these codes then for legal reasons provided you've performed the calculations provided in the pamphlets.

I'd suggest picking up either CGA S1.2 or S1.3 (or both) depending on the system. You can purchase these directly from CGA at this web site:

http://www.cganet.com/publication.asp