Inlet Line to PSV

[RugRat2]

Hello,

I have a question concerning the inlet piping to a relief valve. Similar to foxymophandlpapa but a little different.

The existing[\b] relief valve in question protects down stream piping and equipment (similar to a natural gas header) from a regulator failure. The existing line is a 0.75” with a 1.5” inlet relief valve protecting it. The relief valve inlet line itself is the same size as the relief valve inlet. The protected line has a tee with the straight run portion 0.75” and the branched portion expanding to a 1.5”. The reason behind this is because a relief valve with the inlet / outlet / orifice combination is not offered (probably due to capacity). The regulator itself is probably oversized for the line size. Most regulators are one or two line sizes smaller than the connected pipe, but not the case for this scenario.

The pressure drop is under the 3% allowable inlet pressure drop also.

Is this violating any API recommendations or ASME requirements based on the inlet piping?

Thanks for the help,

 

[dcasto]

I can not imagine that a combination of regulator and relief can not be found.

You must be working with pressures under 50 psia. The pressure drop will most likely be under 3% in you case, but do the calculations. Here's two things I'd do.

1) get a 1 1/2" blind flange and have it tapped with a 3/4" NPT thread. Use that flange as the transition piece, look, no expasion piece.

2) Go to a regulator monitor set up. That is just put two regulators in series.

 

[4Pipes]

Sounds like something is over sized or under sized.

The header is either too small or the safety valve is too big. In my experience, the safety valve body size - orifice combinations are well chosen to fit within normal design guidelines for flow velocity etc. If something doesn't look right and doesn't fit with code recommendations then its most probably wrong. I'd assume something is wrong unless I was seriously convinced otherwise.

 

[zerosum]

Could it be that diverging flow is subject to separation and vortexing and that is not something we want going into an orifice.

 

[zerosum]

sorry, posted to the wrong topic, will repost