Specifications for burying a 4" diameter nitrogen filled pipeline

[TNich]

Some mechanical engineers and I are working on a job where we need to bury a 4" diameter nitrogen filled pipeline. We cannot find anything regarding specifications for burying it (particular minimum/maximum depth, does it need to be wrapped, use a different particular material). I don't want to just assume that these specifications are the same as for above ground. Any reference or pointing in a particular direction would be greatly appreciated.

 

[BigInch]

ASME B31.8 if you want to consider it as a pipeline.
ASME B31.3 if you want to consider it as process piping.
Methods for underground stress analysis as shown in ASME B31.1
All of which can help you decide how you might want to design it.


I hate Windowz 8!!!!

 

[LittleInch]

How long is this section?
Where is it? If inside a plant boundary it is different to outside the fence.

If you don't want it to corrode then yes you need to coat it differently. You probably want to look at cathodic protection if it's more than about 200m or would be difficult to repair if it sprang a leak.

Depth 0.6m min, normal 0.9 to.1.0m.

Is recommend you find a pipeline engineer to advise or do the design for this section.

My motto: Learn something new every day

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

 

[ripaldee]

Additional reading:
API RP 1102 "Steel Pipelines Crossing Railroads & Highways"
NACE RP 0169 "Control of External Corrosion on U/G or Submerged Metallic Piping Systems"

 

[weldstan]

If you don't want it to corrode out, coat and cathodically protect.

 

[zdas04]

If you don't want it to corrode consider skipping steel altogether. RTP (reinforced thermoplastic pipe nee spoolable composite pipe) is my first (and second and third actually) choice for high pressure buried pipe in sizes of 6-inch and smaller (FlexSteel has a new 8-inch product, but I've never laid any so I don't have an opinion on it, I've laid a bunch of smaller stuff and find it to be far superior to steel). It is has higher material costs than steel, but installation costs are a fraction of the steel costs so the installed cost ends up 60-80% of the cost of steel without corrosion issues. I've used it for jobs that were 50 m long. I've used it for multi-mile flow lines. I'm recommending it in my classes for the lines from wellheads to separation on gas wellsites. I haven't designed a steel line smaller than 8-inches in a decade.

I've used FlexSteel, FlexPipe, FiberSpar, and Soluforce and they have all performed as advertised (the list is basically heaviest to lightest, the Soluforce product has arimid fibers for the strength layer and it weighs nothing, FlexSteel has a steel strength layer and is not much lighter than steel pipe). There was one early product (that is no longer on the market) that used a chemical bond to attach end connections to the pipe and it didn't work out well. All the RTP products today use hydraulic crimping and are very easy to install a high-quality connection.

None of that was an answer to "what code?". I have to assume that since you are burying it it is outside a plant fence so I'd look at ASME B31.8. If you are burying it inside a plant fence it is ASME B31.3, but I'm not sure why you'd do that.

David Simpson, PE
MuleShoe Engineering

Law is the common force organized to act as an obstacle of injustice Frédéric Bastiat