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B31.8 Ends and NFPA 54 Begins?

B31.8 Ends and NFPA 54 Begins?

B31.8 Ends and NFPA 54 Begins?

(OP)
Greetings All,

I'm a Canadian engineer and I'm working on a natural gas pipeline metering station in North Dakota. I'm not very familiar with ND code requirements for pipeline installations (ASME B31.8). I've been asked if a PSV/PRV for protecting low pressure fuel gas piping from a regulator failure is required from a design or code perspective. This fuel gas piping is only for a building heater in the metering station. I'm not sure if the relief device is required from a code perspective and I'm not sure if B31.8 still applies at the failure location.

A 40 PSIG fuel gas line (with two upstream regulators in series, set at 100 PSIG and 40 PSIG, and a PSV set at 150 PSIG) is used to feed a building heater via a service regulator (set at 1/2 PSI) to an appliance regulator (set at 7" WC). I've been challenged to show in the code where it says that we do not require a PSV or PRV for over pressure protection from a regulator failure between the service regulator and the appliance regulator (the appliance regulator is only designed to handle pressures up to 2.5 PSI). The service regulator has a built internal relief mechanism but the regulator manufacturer says it is not fit for complete regulator failure.

B31.8 points to NFPA 54 in section 802.12 clause (c) for piping beyond the meter assembly (or the outlet of the service regulator where no meter exists).

According to NFPA 54, the service regulator seems to be the only requirement for pressure protection per section 9.1.18 (2006 edition) and to be installed in accordance with the manufacturer's instructions (section 9.1.1.2). However, if I were to follow B31.8 I think I would need a PSV set at 2.5 PSIG to protect the application regulator from the upstream 40 PSIG. I've never seen a PSV installed in this way and I don't think they even make a code-stamped PSV for this scenario.

Am I interpreting these codes properly? Can I consider this NFPA 54 as the applicable code and rely on the internal relief of my service regulator and the heater designer's installation instructions? Is this failure a risk that should be evaluated by the owner, but not a code requirement?

Thank you for your advice and wisdom.

RE: B31.8 Ends and NFPA 54 Begins?

(OP)
I thought I would update this post with more information after doing more research. For this application B31.8 is the governing code all the way to the building heaters. However, section 845.24 (from B31.8-2013) does not require a PSV for the appliances if the upstream regulator and distribution system meets the requirements of this clause. This clause includes: maximum operating pressure of 60 psig, A PSV set to limit the pressure to 60 PSIG, a few requirements for the appliance regulator, and a few other items. It looks like NFPA 54 should not be included in this design except for perhaps the heater design by the manufacturer.

Hope this helps someone in the future.

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