Relief Valve Capacity

[bgswartwood]

We are being asked to change out all schedule 80 pipe nipples to Double X nipples. The ID of the nipples will be substantially smaller. If the nipple is on the inlet side of the relief, will it affect the capacity of the relief?

 

[Latexman]

It can. It depends on the PSV, the scenario, and the pipe and fittings.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[bgswartwood]

Natural gas plant, discharge piping on a compressor, 1" weldalet, 1" AG relief valve, 985 psig MAOP, minimal discharge piping. Will a double x fitting change the relief capacity? Where do I find written proof either way?

 

[Latexman]

It's not as simple as that IMO. You won't find written proof anywhere, since it is specific to your PSV, the scenario, and the pipe and fittings. Someone knowledgeable in reliefs will have to calculate and document that it is okay, or specify the modifications needed. Basically, the inlet pressure drop (and this probably includes more pipe and fittings than just the subject nipple) should be less than 3% of set pressure at rated flow.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[Latexman]

API 520 Part 1 and Part 2 and API 521 should give you most of what you need to do it, especially API 520 Part 2.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.