2 replies to this topic

[Itineris]

Hello,

 

While working on sizing a PSV I have encountered the following:

 

A vessel with a design pressure of 290 PSIG, which is blanketed with a supply of 110 PSIG nitrogen. Centrifugal pumps feed the vessel, which dead-head nowhere near the design pressure of the vessel.

 

Normally, I would say a relief device is not needed here since there doesn't appear to be a pressure source which can exceed the tolerance of the vessel. However, a co-worker has advised me the vessel should still have a PSV for hydraulic expansion/contraction. His reasoning is that if the vessel is completely filled with liquid and then the liquid inside of it heats further due to thermal radiation, that the warming of the fluid could cause the pressure to rise passed the design pressure as the fluid expands.

 

If the vessel above had a temperature lower than ambient conditions I could see this happening, but in this  case the process is running about 160F, so the heat transfer is moving away from the process, thus I don't see this being an issue. I only see the fluid cooling and contracting.

 

Has anyone sized a PSV for thermal expansion? How did you calculate the maximum expansion rate? When would you apply this sizing as the design case? Thank you for your time.

[fallah]

Hi,

 

You can read the section 5.14 of API 521 Fifth Ed. to find how that standard can be applied to your case. If the system you described is among special cases, you can use the equation (1) in section 5.14.3 to calculate volumetric relieving flow rate due to thermal expansion...

Edited by fallah, 25 June 2014 - 11:55 PM.

[Itineris]

Awesome! That was exactly what I was looking for. Thank you for the API reference Fallah.