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Pipeline Wall Thickness Change?

Pipeline Wall Thickness Change?

Pipeline Wall Thickness Change?

(OP)
I'm working on a pipeline project, a 6"-300# crude oil line, along the proposed routing we have to cross a dry streambed (normally dry 10 months a yr.), the engineers have desided to directionally bore under this streambed and install a 24" dia. casing (large for future applications). One of the engineers on the project is indicating we need to "bump up" the pipe wall thickness fron Sch.40 to Sch.80 ...and is sigthing it as some code requirement. I could maybe understand this but this pipeline is 10 ft. below grade (bottom of streambed) and in a 24" STD. WT. casing. I've been looking at DOT tite 49 sect.195 (I don't have B31.4) to try to find something about this, but no luck so far. Has anyone ever run across this requirement?

RE: Pipeline Wall Thickness Change?

Ask him for that clause...

Also, if you plan on complying with B31.4, you need a copy of that specification.

RE: Pipeline Wall Thickness Change?

There is nothing in the code specifically that requires an increase in wall thickness to my knowledge, but it is a general industry practice that some follow, and B31-4 states:
The design requirements of this code are adequate for public safety under conditions usually encountered in piping systems withing the scope of this code, including lines within villages, towns, cities, and industrial areas. However, the design engineer shal provide reasonable protection to prevent damage to the pipeline from unusual external conditions which may be encountered in river crossings, inland costal water areas, bridges, areas of heavy traffic, long self-supported spans, unstable ground, vibration, weight of special attachments, or forces resulting from abnormal thermal conditions. Some protective measures which the design engineer may provide are encasing with steel pipe of larger diameter, adding concrete protective coating, increasing the wall thickness, lowering the line to a greater depth, or indicating the presence of the line with additional markers.
The general idea is if you can never access this pipe again, to add wall thickness for corrosion allowance, etc. so you don't have to, or lower the risk from time dependent threats. I won't argue whether I think this practice is good or bad.
What I don't understand is why put the pipe in casing if it is an HDD??? You have suffieicnet burial depth where you are under the stream, so won't get scour, wash out, etc. The casing is just going to increase corrosion risk.

RE: Pipeline Wall Thickness Change?

49 CFR Part 195, ―Transportation of Hazardous Liquids by Pipelines,‖ has incorporated ASME/ANSI B31.4 code by reference.

ASME B31.4 403.1:

The design requirements of this Code are adequate for public safety under conditions usually encountered in piping systems within the scope of this Code, including lines within villages, towns, cities, and industrial areas. However, the design shall provide reasonable protection to prevent damage to the pipeline from unusual external conditions which may be encountered in river crossings, offshore and inland coastal water areas, bridges, areas of heavy traffic, long self-supported spans, unstable ground, vibration, weight of special attachments, or forces resulting from abnormal thermal conditions. Some of the protective measures which the design may provide are encasing with steel pipe of larger diameter, adding concrete protective coating, adding a concrete cap, increasing the wall thickness, lowering the line to a greater depth, or indicating the presence of the line with additional markers.

You need a copy of specification B31.4.

RE: Pipeline Wall Thickness Change?

Stick with CFR 195. It is based on B31.4, but (if the project is in the USA) the CFR IS the legal design requirement.
You do not have to increse the wall thickness. The pressure wall thickness design factor of 0.72 is the only requirement for all segments of a liquid line, in all areas, remote country, towns, cities, farmland or under a river, unless your Corps of Engineer's permit says otherwise (for a navigable stream crossing). It is a minimum requirement, so there may be some reason to use wall thickness, such as high axial stress from high temperature operation or something, but there doesn't seem to be a reason to do so, given the info you have provided so far. Especially since it is well below the stream bottom in an HDD bore.

Independent events are seldomly independent.

RE: Pipeline Wall Thickness Change?

My reading of the codes leads to the same conclusion as BigInch, I wouldn't change pipe schedule inside the casing. I had one client who got sick of the water standing in the roadbore casings and creating a great environment for harmful microbes. He fixed the problem by pumping the casing full of liquid paraffin and letting it set up. 20 years later the carrier pipe came out of the ground in perfect external condition. I think that this was a better solution than increasing the corrosion allowance.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Pipeline Wall Thickness Change?

ditto previous postings, but why the casing pipe? it is an unnecessary added expense. there are hundreds of HDD waterway crossings without casing pipe.

good luck and have fun!
-pmover

RE: Pipeline Wall Thickness Change?

He's using the casing so he can pull this pipe and replace it with a larger one, or maybe multiple pipes in the future.

A gas line might require a thicker wall, as design factors might vary if it was considered a fabricated segment.

Independent events are seldomly independent.

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