Liquid relief valve piping (ASME B31.1 NBEP)

[mbsterli]

Hello all,

First post...

I'm assessing discharge piping of multiple liquid pressure relief valves installed on the downstream side of chemical metering pumps. Each is situated within ASME B31.1 Nonboiler External Piping. The relief valves each have a 1/2" MNPT inlet and 1" FNPT outlet, with a 'C' orifice (0.062 in2 orifice area). Currently the inlet piping to the relief valves is either 3/8" or 1/2". The discharge piping is either 3/8" or 1/2" leading back to the chemical storage tanks.

Section 122.6.2 of ASME B31.1 states that "Sectional areas of a discharge pipe shall not be less than the full area of the valve or device outlets discharging thereinto". My initial interpretation is that all discharge piping must be at least 1" in diameter (to match the 1" FNPT outlet). Is that correct? Or is the "full area of the valve" referring to the orifice area, in which the existing installation would be okay?

As the metering pumps provide such low flows (between 0.5 and 20 GPH), the existing piping is large enough as to not create excessive backpressure and inhibit the pressure relief. Should the piping be changed out anyways?

Thanks

 

[GenB]

1- The B31-1 is for BEP and I do not think apply to the referenced PRVs.
2- you shall nor reduce pipe size on RVs so its not the orifice dia. but the pie outlet dia. that goes for any PRVs. you can reduce them if not Code bond valves,
in your case of liquid relief of small amount of liquid just to relief mcro-pump overpressure, you may be okay. just my comments not a recommendation.

 

[mbsterli]

Thanks GenB

According to 101.2(B), NBEP is covered in ASME B31.1 as well

If it is the case that the discharge piping can be no smaller that the PRV outlet (which is a 1" FNPT connection), is there no distinction between different pipe thicknesses? i.e. I could install 1" Sch 5s with an ID of 1.185", or 1" Sch XXS with an ID of 0.6" and there would be no distinction between the two according to code?

 

[Duwe6]

There is an assumption that STD wall // Sch40 piping is being used for the discharge piping. And for your condition, 1"NPT piping is indeed required, your PRV having a 1"FNPT discharge outlet.