Stress Analysis for Reinforced Thermoplastic Pipe

[if7005]

Hi All,
I want to ask for any expert here, how to perform stress analysis for above material and what kind of code/standard ? Is BS7159/UKOOA ( for GRP/GRE pipe) applicable for it ? The pipe will be buried with 8" size, 60 C.deg, and
2300 psig, with 30 km length as water pipeline.

Rgrds,

 

[LittleInch]

If you mean stress analysis in the classic sense of rigid pipe then I think you won't find any information as this stuff is too flexible and doesn't respond to the same inputs as steel / GRP. I suspect, a bit like GRP/GRE, that each vendors wrap and system will generate different Youngs modulus and different stress / strain and thermal expansion criteria, but the hardest will be finding out the accpetable limits.

RTP is great looking stuff, but applying rigid pipe design to it won't work - in my opinion.

My motto: Learn something new every day

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

 

[rconner]

Sounds like maybe a little "stretching of the envelope" (so to speak) here, and a good question asked. I thought e.g. ANSI/AWWA C950 for such material water pipes only goes up to a maximum of 450 psi Pressure Class (out of many classes available) pipes, and you are apaprently wanting capability at more than 5 times that. While I'm sure there are some exceptions e.g. in the oil patch, I believe most composite water pipes are used at far less pressure. Let us know how it turns out.

 

[DSB123]

As rconner says the pressure you specify is rather high for the material. Have you actually calculated what thickness you need to withstnad the pressure?

 

[zdas04]

Rconnor,
Are you thinking of HDPE or RTP? The numbers you quoted are in the ballpark for HDPE (a little high, but with some derate of effective life, I can get there in water service). RTP is rated MUCH higher. FlexSteel has a 3,000 psig rated pipe in sizes up to 8-inch. FiberSpar has a 2500 psig rated pipe in up to 3.5 inch. Soluforce and FlexPipe both have products rated over 2,000 psig in 3-inch. I've used this stuff at 1400 psig with great results. I see no reason to think that you'd have problems at 2300 psig.

As to calculating hoop streses, take a look at API RP 15S or API RP 17J. I'm not sure how you go about doing a Caesar type analysis with this stuff. When I've tried to run it in Caesar II, I've gotten meaningless results.

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"

 

[MJCronin]

ASME B31.1 and B31.3 contain rules and guidelines for FRP and other plastic piping systems.

The latest version of CAESAR-II is able to perform a stress analysis of these systems.

I am also curious about "Reinforced Thermoplastic Pipe" at 2300 psig........ really ? What kind of plastic valves are you using at that extreme pressure ?

What is the wall thickness of the RTP piping for this pressure ???

MJCronin
Sr. Process Engineer
Venture Engineering & Construction

http://www.VentureEngr.com

 

[LittleInch]

MJCronin, FRP is still basically "solid" pipe. The stuff the OP is talking about is essentially flexible pipe. Google some of the names zdas04 quotes and you'll see the difference. You end this stuff with standard flanges which you connect standard valves to. It's great stuff, but a bit limited on size and you can't design it the same as steel or gre.

It's all plastic pipe with loads of reinforcement as separate layers, some use steel, some kevlar and how you analyse it god only knows.

My motto: Learn something new every day

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

 

[BigInch]

You can't stress analyze it in the classical sense. Pressures are based entirely on test results and vendor's proprietary stress prediction and wrap design materials and methods. Installation is based on avoiding any condition which would produce stresses other than hoop stress within stated ranges. The weak link is the connection between segments of finite manufactured lengths and at inlets and outlets.

As such, this material may or may not be permitted for use in CFR/DOT regulated piping systems only by filing for a special use permit issued by PHMSA for each particular installation, and only after public comments have been taken and the design and other peculiarities of the installation have been reviewed and approved by the agency, more with an eye towards allowing it under a proprietary "equipment" classification, rather than by proving adequacy by meeting any particular pipe design criteria of the various codes. As far as I know, there has been only one instance that might (or might not have) been approved for installation in a regulated system (in Los Angeles during the summer of 2012). I was following it for a time, but got busy on other things and never looked back to see if it was ever actually approved for use, or not. I suspect it was.... but I don't know for sure. You might look into the PHMSA online "special use permits granted" files to find out yourself.

Independent events are seldomly independent.

 

[zdas04]

This stuff is approaching 20 years in service. I've used it for all sorts of non-jurisdictional applications for raw gas and water. I did a design for a CO2 injection enhanced recovery application that fit RTP perfectly (the project never got past design, capturing the CO2 from an amine stack was just too expensive). I haven't followed the progress with the PHMSA because I'm just not doing much work in the States these days. I think the FlexSteel 8-inch product is going to open up a new world of applications that are going to force the Feds to extract their heads from the sand.

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"

 

[rconner]

The world is at least three-dimensional. While legacy pipe materials have very close to the same strengths in all directions, most now promoted "reinforced" products (and many codes consideration) do not. We shall see what the importance of these observations is in the future.

 

[zdas04]

One of the RTP's (FlexSteel) was designed for offshore use. The two key differences between offshore and onshore are: (1) when the pipe is in water you always have some amount of external force (that may be greater than internal force); and (2) ships anchors will drag across the sea floor. Designing a product robust enough not to collapse when internally depressurized under 100 m of water that can hold a supertanker in a gale was a serious Engineering challenge. FlexSteel has stood up to that kind of 3D loading for two decades. I'm betting a lot that it will stand up to anything that a steel pipe would stand up to (and steel pipe does not always stand up to anchor drags).

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"

 

[if7005]

Metallic reinforced plastic pipe with >6" size, sounds like the great material instead of steel pipe,even better for corrosive water pipeline service in low temperature. But pipe load in service always the combination of P,T,&external load in 3 direction, and we cannot predict with any code how it will be fail. I can only believe in all dependence qualification test (burst,tension,crush test,etc) and get it all (and witness), then wait and see.

zdas04(Mechanical), how long have you use this kind of material, what's the size, P, and T, and how to conduct real time leak test/inspection if it is buried pipeline service ?