Block valves on PSV discharge

[PRV2]

Hi, I am wondering if anyone is aware of a code that restricts the number of car sealed open block valves allowed on a ASME Section VIII PSV discharge. I need to hot tap a flare line to add a skid with a relief valve which will leave it with two block valves on the discharge permanently. I am not aware of a code against this as long as the valves are full port, car sealed open, and the built up back pressure is incorporated into the sizing of the PSV. Let me know if you know otherwise.

 

[pennpiper]

What size will these valves be?
What type of valves will these be?
Why can't this modification be done without having valves involved?

 

[PRV2]

3" 150# x 4" 150#, pilot operated relief valves, impossible to ensure system is isolated and purged without the valves

 

[PRV2]

The block valves are 4" 150# full port gate valves.