Flowline design ASME B31.8 or ASME B31.4? 1

[141109]

Our flowlines from the well head to processing plant contain well fluids which is a mixture of oil and gas though mostly oil. Can anyone advise if flowlines always need to be designed to ASME 31.8 to account for the gas content or if there is a fractional gas content cut off that allows use of ASME B31.4 to be used? The codes themselves do not appear to advise on this.

 

[LittleInch]

Ha,

The B31.4 / 8 codes don't advise because they don't officially cover flowlines - either of them.

This has been proved in a code interpretation 16.13-2 for B 31.8 -

https://cstools.asme.org/Interpretation/InterpretationDetail.cfm?TrackingNumber=17364

[My emphasis]
"Question (2): In accordance with ASME B31.8-2007, does the Code exclude flow lines between gas production wells and gas separation facilities?

Reply (2): Yes."

No one seems to have asked the same question for B 31.4. The scope doesn't mention "flowlines" or well heads and the diagram for scope is a little vague, but doesn't really show a flowline type scope.

However life being what it is people just use them anyway and many just make a decision between B 31.8 and 31.4 based on whether this is a "gas field" with condensate or an oil field with some gas... Some use B31.8 for everything with a bit of gas in it, some use B 31.3 (not many), some use other codes like ISO 13623.

The cutoff is completely arbitrary so you could use more or less than 50% liquid fill in the pipe, more than say 10000 GOR is actually a gas field or some other state or country definition as to whether it's one or the other.

If it's mainly Crude Oil then I would use B31.4, state that in your design basis and let someone else argue it otherwise.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

The B31.4 diagram can get vague as LittleInch says, but IMO it is only vague for flowlines connecting to something that is not some kind of processing plant or pump station, such as well to a gathering field collection tank battery and the like. B31.8 does not cover them at all, so again my opinion, B31.4 is the "most applicable". However gas companies have been known to use B31.8 EVERYWHERE, despite high water, oil and condensate production and oil producers use B31.4 nearly always. I have not known of any regulatory objection to use of either for whatever mixture you've got in the pipe. The end result is similar in most cases, except when design factors change entering the stations themselves, or near offshore platforms. What's your company logo say?

 

[141109]

Interesting. Thanks for your response.
31.8 does say 'does not apply to... wellhead assemblies, including control valves, flow lines between wellhead and trap or separator, offshore platform production facility piping, or casing and
tubing in gas or oil wells' but I took that as well head associated piping (with separator on the well pad) before it reaches the pipeline / flow line pig trap/ connection and from there it would apply.

Yes but no guidance on what may or may not be applicable depending on amount of gas present in well. I note Texas state appears to say 100,000scf/sbbl GOR makes it a gas well, but GORs lower than this still have alot of gas which would need to be considered and not necessarily covered by 31.4.

 

[1503-44]

GOR break point is defined for tax code and administrative purposes, so it isn't relevant for use in engineering design.