Buried VS Above Ground Production Piping

[10815L]

Hi all,
we are in discussion for production pipeline, connecting from well to production header and total length is 4 Km, High pressure 700 psig.
safety point of view buried piping is ok and cost point of view above ground piping is ok but i would like to konw what is best option for production piping bring to the production header. Dear experts please share your exeprience.
Thanks
10815l

 

[LittleInch]

If by above ground you mean laid on the ground as opposed to using supports, then it depends on what the hazards are to your pipe and how big it is. If it's small enough to drive over, that's exactly what will happen reardless of any signs you put up - would it withstand an excavator going over it??

Above ground you really need to lay in a gentle curve or include expansion loops as the pipe will move a lot more than buried pipe as there is much less friction holding the pipe and movements are more like offshore where large movements occur, especially in desert conditions when there is no flow and lots of sun. Corrosion and coatings also become an issue as CP doesn't work, but even in deserts, you can get corrosion under the pipe.

In my opinion, you should always bury it - it's much more protected and you need to think what is the cost and environmental impact if my pipe leaks / ruptures because it flexed too much or because someone drove over it. 4km is not far so I can't believe burial will be that expensive.

Some contries require pipes to be buried, especially gas, but "oil" lines are seomtimes not included. For 700 psig, i would always go for buried. Too much risk otherwise.


My motto: Learn something new every day

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

 

[10815L]

Hi,
But Shell DEP state for pressurized hydrocarbon piping buring should be avoided? in our case production line is high pressure also.
Thanks
10815l

 

[zdas04]

The Shell DEP's seem to be a de facto standard in many places. I've never worked in any of those places so I don't have an opinion about how valid that elevation is, but if they say things like "burying pressurized hydrocarbon pipe should be avoided" then I wouldn't put much store in them.

ASME B31.8 has detailed data on burying gas pipe and no admonition about avoiding burying it. There are certainly millions of miles of pressurized hydrocarbon piping buried in the world (probably tens of millions), and the data from those installations indicate that the incidence of failure is less with buried pipe than with surface pipe. Road graders and random bullets have a hard time getting to pipe that is a meter under the surface.

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.
The plural of anecdote is not "data"

 

[LittleInch]

Which DEP and which section.?? Please quote the wording.

I can't see it until later, but I find it difficult to believe, unless its been misinterpreted. Normally the DEPs are quite conservative.

Which county is this in?

My motto: Learn something new every day

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

 

[10815L]

Hi,
Shell DEP 31.38.11-Gen, page 29 and section 3.4.1 states for buried lines.please clarify it and elaborate further on this point.
Thanks
10815l

 

[BigInch]

DEPs are a defacto standard for countries that don't have any standards, don't want to make their own and have some political objection to ASMEs. There is no reason to follow them, unless you don't have any better ideas (and there are plenty), or it's a Shell project, otherwise Exxon-Mobil, or company X are just as valid. NOT. Don't get me wrong. There are some good things... and some bad things about Shell DEPs. Do the good things. Don't do the bad things, or the way to expensive things. Two launching valves on a pig launcher IMO is a waste of money and may be more dangerous than one (IMO)... etc...

If it's high vapor pressure in hot climates, you'll have 2 phase flow in the summer and your pumps will cavitate. In northern climates any water may freeze, or you may have to insulate, or heat.

Why bury production field pipe? You want to keep it a little more safe. In a lot of countries, if you bury it, you'll never find it again. Same can be said for leaving it above ground. Leave it above ground in Nigeria and first you'll have no oil, then no pipe. If you got the money, bury it. If you don't... leave it above ground and cross your fingers.



Independent events are seldomly independent.

 

[SJones]

The DEP under discussion is for on plant piping, not pipelines. If you want the Shell way for pipelines, consult DEP 31.40.00.10-Gen (the '40' is for pipelines) where you will have to have a copy of ISO 13623 to hand, just to annoy Big Inch! You will be guided in your choice by the risk assessment requirements.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[rconner]

Not sure any hard and fast rules here, but stuff happens. Also not sure there is much published research on the subject, but others have noted seems like it happens at least a little more often (at least on a relative mileage basis) to aboveground sections of pipelines e.g.

http://www.marketwatch.com/story/freak-car-crash-shuts-down-major-us-oil-pipeline-2012-03-04

.

 

[zdas04]

rconnor,
The national-news level of these events happen seldom enough to be memorable. I remember one that shut down I-25 through Denver along with the Denver Rail Yard for 2 days in the 90's. I remember one in LA in the 2000's, but not any details. They happen. On the other hand, pretty much everyone who's ever had operational responsibility for Oil & Gas pipe have local-news or no-news stories about road graders and hot rodders that didn't make the national news.

We had a very high pressure CO2 line running on the surface through my county in the 90's. They buried road crossings and just dropped the rest on the surface (plenty of undulations for expansion and contraction). The line was pierced by rifle bullets at least 3 times in the year it was in service. I think there was also a road accident that broke it, but I never got the details on that. There is also a buried high pressure CO2 line running through the county that has never had any drama at all.

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.
The plural of anecdote is not "data"

 

[LittleInch]

10815L, As S Jones notes the DEP you refer to - DEP 31.38.11-Gen is for piping and in the scope of that document, section 1.1 specifically states "Pipelines are specifically excluded from the scope of this DEP"

What you have is a pipeline, therefore if you are using the DEP system, then, as Mr Jones says, use 31.40.00.10. In this DEP, which amends and adds to ISO 13623, section 6.8.2.1 which in the ISO codes refers to burial depth, adds "Any non-buried pipeline sections shall be justified on an individual basis, and shall be
installed clear of the ground to avoid external corrosion."

Therefore in line with my previous post and some of those above, burial is recomended, as simply laying it on the ground is not permitted under the DEP and the cost of supports is often similar to burial costs and you need to justify it in a report.

I've seen buried lines and above ground line son many oilfields, some Shell operated and some not. Only you can make the judgement as to what your risks are and wheter they can be mitigated to prevent damage to your line. If you do lay it on the surface, allow for specific crossing points every km or so which will help to stop people driving over it at random locations.

My motto: Learn something new every day

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

 

[BigInch]

And be prepared for some big thermal movements, if nothing else.

Independent events are seldomly independent.

 

[zdas04]

That above ground CO2 line I mentioned above would end a sunny day 3 m above the top of each and every hillock. By morning the pipe was 1/2 m above the bottom of every vale. Some serious thermal movement over 65 miles.

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.
The plural of anecdote is not "data"