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Design and testing of double containment pipe

Design and testing of double containment pipe

Design and testing of double containment pipe

Hi everyone,

I'm looking for past experience or knowledge of how a double containment or jacketed pipe is designed, tested and certified in the US (or anywhere else for that matter).

Details as much as I can disclose.

It's a metal (Carbon steel) pipe in pipe pipeline (i.e. outside of the plant fenceline) a few kms long (<10). Inner pipe 8",Outer 12". The design pressure is 250 psig. The intention of the annulus is to insulate the inner pipe with material which can't be allowed to get wet. The inner pipe has a hoop stress value <20% of SMYS. The owner currently wants the outer pipe to be double containment in the event of failure of the inner pipe, so the outer pipe has the same design pressure.

This is being designed to B31.4 and is covered I understand by CFR49 part 195.

The dilemma or issue at hand is how to pressure test the outer pipe. Double containment or jacketed pipe doesn't seem to appear in any piping or pipeline code I've seen and hence the issues of:
1) Inner pipe collapse or
2) Can't hydrotest the outer pipe (and would be difficult to drain it even without the insulation issue)
are not addressed anywhere.

I'm recommending writing a deviation to test the outer pipe to 100 psig in air whilst also pressurising the inner pipe to the same or higher pressure to prevent collapse and adding extra testing of the welds and pipe before construction. Can't think of anything more at the moment.

The latest B31.4 (2019) allows a leak test for pipes with a stress value of <20% SMYS, but the current version really doesn't change much between a strength test and a leak test. Specifically if your test pressure of 1.25 x DP is more than 100 psi (ours will be), it specifically excludes a pneumatic test (!). Previous versions of B 31.4 didn't have that wording.

The CFR similarly has no wording to deal with this.

How has anyone tested the outer pipe for e.g. steam jacketed pipe?
Any other experience of double containment pipe testing you can share?

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

RE: Design and testing of double containment pipe

I don't directly deal with them, but here in California, especially in pharma facilities, these type systems are getting quite common, especially near the coast.

I asked an engineer we work with frequently who does a lot of this kind of work, his first suggestion was to take a look at this, https://www.accessengineeringlibrary.com/content/b...

He also pointed me to this, https://www.arlis.org/docs/vol2/point_thomson/1132...

Not my field but maybe you can find something helpful in this?


RE: Design and testing of double containment pipe


Many thanks for that information. Looks very useful. It would be great if you could ask him if they test the outer pipe and if so how.

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

RE: Design and testing of double containment pipe

Got a pretty short reply to that question, mainly "it depends".

Many of the systems he deals with are plastic or composite piping, they specifically do not use air for testing. Metallic pipe systems he said can be either air or liquid pressure tested, but how to test and actual test procedure are defined by system designer.

We did a project in Alaska where the fuel and oil piping was double walled and insulated, and I remember a several page testing procedure, but I was not directly involved with that part of the project so I'm not sure exactly how it was done. My only part of that was verifying the cleaning and pickling after the initial pressure testing. I do remember after the cleaning procedure a second set of pressure tests were performed, along with the final testing of the leak detection system.

Sorry don't have more details, MikeL

RE: Design and testing of double containment pipe


I have experience for the sleeved road crossing and jacketed pipes ( which the sleeve pipe is leak tested for a typical 35 kPa air test ).

You did not mention the type of insulation, spacer and if the pipe is buried or above ground.

I looked to my past documents and books and found the followings,

- Piping hand book ( NAYYAR ) Chapter B13. Double Containment Piping Systems (by Christopher G. Ziu )


- Bioprocessing Piping and Equipment Design ( by William M. Huitt ) suggests air test pressure not to exceed 15 psig.

- One of company standard states ; ( for jacketed piping, the inner pipe shall be tested first. All joints of the inner pipe shall remain accessible during testing. The test pressure for the inner pipe shall be governed by the allowable
working pressure of the inner pipe or of the jacket pipe, whichever pressure is the higher one. The allowable
working pressure in the jacket space shall be decisive for the test pressure of the jacket pipe

Quote (It's a metal (Carbon steel) pipe in pipe pipeline (i.e. outside of the plant fenceline) a few kms long (<10). Inner pipe 8",Outer 12".)

A few kilometers .. this is substantial amount of potential energy in the case of air test..i do not want to mention the risks since i am sure you are aware..

My gut feeling is,

- design the inner and containment piping as per ASME 31.3 and 31.4

- hydrostatic test the inner pipe to test pressure,

- drop the inner pipe pressure to design pressure and air test (if remote area )the containment pipe to ( allowable air pressure specified by local safety codes ..)


RE: Design and testing of double containment pipe

cat serv - thanks for asking and I'm getting the same idea - it will need a very specific testing regime and that's what I'm advising - a special exemption to the normal testing system.

HTURKAT - I'm being a little coy due to confidentiality issues, but the insulation is fibre wrap type which cannot get wet. It is wrapped around the inner pipe and then simply rests on the outer pipe. For a number of reasons it is not really practical to make a long section of outer pipe and then thread the inner pipe in, although I am tempted to suggest that as a worst case solution.

Thank you for the references - I will investigate and may well purchase. The top one is also one of the links from car serv.

Air testing is as you know a fairly contentious issue, but I am generally in favour of it provided that suitable precautions are taken. The potential for a rupture is very low due to the low % SYMS of the pipe (<30%) at which point pipes leak and don't rupture. however pneumatic testing gets people very agitated for good reason, but sometimes they don't listen to the arguments for... It is mainly buried but has some sections above ground on racks.

The biggest issue we face at the moment before we go talk to the regulator / AHJ, is that we can't really follow the CFR and B31.4 to the letter, so need to agree an alternative with extra quality checks etc. I'm not sure at the moment if the insulation will still be as good after an air test or not. Usually the outer pipe is not classified as double containment but simply there to protect the insulation, but in this instance the client wants it. That's also another line of attack is to make the outer pipe non double containment or lower the design pressure with suitable relief valves to get us into the range where we can follow the codes and air test up to 100 psi.

Tanks again for the input - it helps clarify the issues and gives some more background to a non standard situation.

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

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