Wellhead Piping (Downstream of Choke Valve) 1

[moeedalam01]

I am currently working on a project that includes gathering of 30 nos. oil / gas wells in plant manifolds and then setting up a gas processing plant which removes CO2 from the stream vide Amine Sweetening Unit Along with Mol Sieve Unit for removal of water. Condensate and LPG is extracted also. There has been a confusion in application of piping codes. I have researched that ASME B31.3 will be used for complete plant piping (including process and utility piping) and B31.8 will be used in designing of flowlines (pipelines)for gathering 30 nos. wells.

My question is which piping code will I use for wellhead piping (downstream of choke valve on Christmas Tree) till the line becomes underground onward to the plant manifolds?

B/c during discussions, we usually find to distinguish b/w B31.3 and B31.8, some say wellhead piping will also be on B31.3..... but I want to know what is the right practice.

Appreciate your guidance

 

[LittleInch]

moeedalam01,

Strictly speaking, B 31.8, in the scope section, 802.1, b (5)(This code 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

However it is commonly applied to flow lines, even though it is not officially part of the scope of the code.

Normal practice I have seen and used on wellheads is to use B 31.3 D/S of the choke valve with B 16.5 flanges up to the connection to the flowline where it leaves the wellhead plot.

I've seen wellheads with API 6A piping and flanges, but less common.

The only reason to use B 31.8 would be to make use of the higher strength steel, but for normal wellhead piping sizes (4,6, maybe 8") this makes no difference in thickness and just complicates life with different grade flanges and fittings.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[weldstan]

B318, B31.4, and B31.3 have all been used oil/gas gathering systems.