Check valve leakage rate basis/philosophy for PSV sizng

[compo]

I am trying to get feedback from the wider industry on the basis/philosophy considered/used for establishing the leakage rate back through check valves in view of calcualting required relief valve size to protect the upstream section the check valve is leaking into, this is specifically the case where two check are provided in series and one is considered to have completely failed and the other has a leakage rate based on for example a) ?? percentage of forward flow or b) ?? fraction of check valve rim face or area or c) any other basis.

I am sure many design and operating companies follow varying philosophy, if you can help and share your experience and company standard and / or point me in a direction of a guidance document or paper you may know of such as a international standard. Thank you all in advance for any guidance you can afford.

Regards,

 

[Chance17]

one major oil refiner allows evaluation at 10% of forward flow.