dissimilar check valves for pressure protection

[sarahf197]

Hello,

I was wondering if anyone had any advice on the following:

I have one fluid flowing into a header which although is normally at lower pressures requires a 600# flange rating due to the pump shutoff conditions. The fluid flowing into the header only requires a 300# flange rating considering only its upstream conditions. So does the entire system have to be 600# or could say two dissimlar check valves be put on the low pressure line that way if the high pressure line was to ever be blocked in it could not flow back into the low pressure line exceeding the flange rating.

ASME B31.3 Section 302.2.5 "When two services that operate at different pressuretemperature
conditions are connected, the valve segregating
the two services shall be rated for the more severe
service condition...." does this mean that a valve such as the check valves as described above if specified as 600# can be used to separate the two pipe specs?

Thank you for any opinions or past experience

 

[SNORGY]

Without thinking it completely through by inspection of your P&ID:

Try, on the low pressure (300#) side in direction of flow:

(1) line to 600# class flange = the "spec-break"
(2) 600# flanged check valve
(3) 600# spool (or bleed ring if spec permits) with one vent / drain sw x scrd valve c/w plug in one connection and and one 3/4" x 1" or thermal PSV in a second separate connection routed to HC drain, flare KO or suitable location
(4) 600# flanged check valve
(5) 600# flanged isolation valve separating low pressure header from high pressure header

Size the PSV for some factor of the downstream check valve failure leakage rate; for liquid flow, a thermal PSV would likely work but it needs to be looked at carefully. I think there might be an API RP-520/521 guideline for this but to be honest I don't have it in front of me at the time of this posting.

Regards,

SNORGY.

 

[BigInch]

Check valves are NEVER considered to offer pressure protection.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/