ASME VIII, Div 1: UG-135 PRV Inlet Size 1

[jnleroux]

UG-125 states that all pressure vessels within the scope of this division, irrespective of size or pressure, shall be provided with pressure relief devices...

UG-135(b)(1) states The opening through all pipe, fittings, and non reclosing pressure relief devices between a pressure vessel and its pressure relief valve shall have at least the area of the pressure relief valve inlet.

API 520 defines inlet size as the nominal pipe size of the PRV at the inlet connection, unless otherwise designated.

With this in mind, I have a scenario where a small vessel empties into a much larger vessel with essentially no pressure loss between the two vessels. There are no block valves between the vessels. The larger vessel is protected by a PSV with an inlet that is larger than the pipe between the vessels. The design pressure of the smaller vessel is much higher than the larger vessel and set pressure of the PRV. All principal sources of overpressure evaluated do not overpressure the smaller vessel.

I am unable to find anything in ASME or API that allows for this scenario.

Has anyone found a section in ASME or API that addresses this type of scenario?

Thanks,
John

 

[EGT01]

John,

It is not uncommon for a single relief device to provide overpressure protection for more than one component in a system. Have a look at the appendix in API RP-521 that addresses "Special System Design Considerations" and in particular "Single Pressure Relief Device Protecting Several Components in a Process System".

Additional information can be found in ASME Section VIII, Appendix M that addresses "Stop Valves Between Pressure Relieving Device and Vessel". Appendix M also references UG-133.

 

[panduru]

"I am unable to find anything in ASME or API that allows for this scenario."

Much before going out to find anything in the Codes, I would feel it's only natural that the pipe between the vessels constitutes a critical element in the pressure system, irrespective of any other factors you mentioned.

 

[jnleroux]

Follow up note: ASME Code Case 2211 allows for this situation, subject to jurisdictional approval.