We are a custom designed process equipment manufacturer. I have spent a couple of days trying to determine whether or not a proper PSV is required to vent a horizontal atmospheric expansion tank. The tank contains Class IIIB Heat Transfer Fluid (HTF), and there is a 3/4" breather vent (through a desicant filter to keep moisture out of the HTF) at the top centerline which is continuously open to atmosphere. Our typical expansion tanks range from 20gal to 300gal. I have attached a word document that shows the basic system. Note that the expansion tank has a single riser that services two process loops.
Our engineering department has recently proposed using a check valve to relieve increased pressure due to external fire. They have properly sized the orifice requirement, and argue that the probability of a check valve failing to open is orders of magnitude lower than that of a PSV. I am trying to find out if this is allowed, and if there are any requirements that we are missing. It is not clear to me whether any emergency relief is required for this situation beyond protecting the tank or connected piping from bursting due to pressure rise due to external fire.
Most sources that talk about fire venting of low pressure and atmospheric vessels reference API 2000, Appendix C. Should I purchase this standard just to have that reference? Or does it not apply to our case?
Thanks in advance,
Dan Gunderud
email address
Product Safety Manager (Ex- Electrical Engineer)
Buffalo, NY.