NFPA 59A Fuel Gas service within LNG plant 2

[LuffyD]

NFPA 59A requires 30%RT butt welds ( above -29C) as per 9.7.3.2 (B) Pressure piping operating above ?20°F (?29°C) shall have 30 percent of each day’s circumferentially welded pipe joints nondestructively tested over the entire circumference, in accordance with ASME B 31.3.

1- is Fuel Gas service(same composition/pressure than Feed gas) falls under this requirement ?

code looks confusing.
in one hand , all HC pipings should follow NFPA 59A in LNG plant
as per 9.2.1.1

and in the other hand 9.2.1.2 Fuel gas systems shall be in accordance with NFPA 54, National Fuel Gas Code, or ASME B 31.3, Process Piping.

nfpa 54 Exept FG for LNG from its scope.


so the question is : FG should have 5%RT butt weld as B31.3 or 30%RT as any HC withing LNG plant.

 

[dcasto]

It's your choice. Personally I'd adopt the same code for all piping in the plant to minimize confusion and possible paperwork errors, which is just as bad as a physical error these days.

 

[DLite30]

NFPA 54 is regulates low pressure fuel gas installations mainly for domestic use, like gas stoves or ovens.

Industrial fuel gas should still follow 31.3

 

[LuffyD]

many thanks

the question now is why FG remains B31.3 ( normal fluid service ) while it's Slip stream from LNG Process Gas which is NFPA59a. consequence of failure of FG or Process gas for same pipe size would be the same, if both come from the same feed gas.

 

[DLite30]

The way I read it, is that 59A overrides the 31.3 examination requirement in section 9.7.3, such that 30% is still required, and makes no distinction between fuel gas piping or other pressure piping...it's all pressure piping.

The section that you originally referred to in 9.2.1.2 only means that aspects of the piping design shall be iaw 31.3 and then later in section 9.7.3 is where the examination requirements discussed.

So, it all should be examined with 30% in mind.