Hello, I have a question concern

[RugRat2]

Hello,

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

The existing 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,

 

[pleckner]

Piping falls under the scope of ASME B31.x and the requirements are different than those of ASME Section VIII, Div. 1. API RP520/Standard 521 doesn't enter the picture either. Now if this same PSV is protecting ASME coded equipment also, then yes, your situation would appear to be the same as for @foxymophandlpapa (other Post).

I've come across this same scenario before and have recommended that the pressure regulator be changed to one of a more proper design and this would have removed the dispartiy between line size and relief capacity (at least in my case).

Another "out" would be to put in a restriction orifice after the regulator to limit the relieving rate due to regulator failure. If there are other scenarios for the protected vessels, well that re-introduces the problem we've been discussing.