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Multiple Psv Installation And Pressure Test

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#1 Alex1


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Posted 13 February 2018 - 09:28 AM

Hi everybody,


When I have a large relief flow, I used to apply the rule described in the APi520 part 1 about multiple PSV with  stagerred settings.

I defined the set pressure of the first PSV at SP= 1 X MAWP and additional PSVs at SP=1,05 X MAWP.

In accordance to ASME VIII and the API520 the accumulated overpressure will be 116% (or shall not exceed 116%)


Most of my equipments are cryogenic equipments, means no hydrostatic test can be performed, only pneumatic test (due to the risk of moisture contamination)


In ASME VIII div1 it's clearly described that pneumatic test should be performed at 1.1XMAWP. 

But there is another rule in ASME which is "the overpressure limit shall not exceed the test pressure".


So I performed a pneumatic test at 110% of the MAWP while I designed the relief devices with an accumulated overpressure of 116% of the MAWP.


Where I'm wrong? 

-Because I performed pneumatic test, I cannot use the multiple device rules with staggered settings?

-Should I increase the pressure test (it will be stange...and dangerous)

-Should I defined a set pressure lower than MAWP? 


or I'm compliant with ASME and API and everything is alright but I don't know why? 




Thank you for your reply



#2 fallah


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Posted 14 February 2018 - 01:46 AM



If you have to use multiple PSVs, the best option is reducing the set pressures such that the relieving pressure of the additional PSV being equal to or less than the test pressure.

#3 Alex1


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Posted 14 February 2018 - 03:22 AM

Noted, thank you Fallah,

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