Hello,

I need some help regarding stress Analysis for Plastic Piping.

One of our customer is using Polybutene (PB) pipework which is currently having leaks. They have used Metallic T- connection for branches.

I have been requested to do a stress Analysis on this Plastic Piping having this metallic Tee connection.
Could someone as to what material would need to be considered for my Analysis . Is it FRP/ GRP (Material No: 20) ?
The reason I ask is because plastic pipe is a bit from FRP/GRP.

And I was looking at using the code ISO 14692. Is this a correct approach?

Regards
AjMat

Hi Ajmat,

I have found this definition thru google.

"Polybutene and polyisobutylene are liquid oligomers widely used as plasticizers for high-molecular weight polymers, such as polyethylene, and as carriers and lubricants. They are not to be confused with the high molecular weight polymer polybutene-1."

Seems like it is not considered FRP or GRP. So I think ISO 14692 is not applicable in this case.

My experience with HDPE piping (not sure if it is the same) is we ask some vendor guidelines regarding support spanning and loop sizing. We have done some crude calcs using beam analysis software but I think the result will not be so accurate due to large displacement. This is just to estimate nozzle loads on pumps (using Elastic modulus and other physical properties to be inputted in software).

I'm not sure, but I think there is no solid "Code" regarding tackling stress analysis of "Polyethelene Plastic Piping".

In your case, the job seems like a trouble shooting work on how to eliminate the leak.

Not sure how to prove it analytically. I'm interested to know also from other fellows how to prove this.

From my point of view, I would handle it this way. (If the leak is on the metallic T- connection). I would do this steps.

1) Visit the site and see if the leak is due to cracks in the tee body itself or in the joints?

2) Check for possible fatigue sources such as pressure cycling. Maybe you can ask operation guys regarding it's operation history.

3) Is there over pressurization of the line?

At the end, maybe your suggestion to the client is to add more material on that leaking point. To quantify how much material is needed you need to identify what's causing the leak and maybe perform some crude calcs.

But in the end, it's hard to guarantee it unless you really have a solid backup on how to eliminate the leak.

Anyway, I'm interested to know the solution to this problem.

Just correct me in case I've made some wrong statements.

Any other opinion is highly appreciated.

Cheers,

Your material is a thermoplastic. ISO 14692 is for (reinforced) thermoset resins. The B31 codes provide no confidence in evaluating thermoplastics' flexibility (e.g., see B31.3 para. A319.1.2).
I believe a soon-to-be-released piping code (NPPS NM.1) will address these concerns.
Here's an informative link for information on NPPS NM.2 - the proposed standard for thermoset resins (FRP pipe). A New Standard for FRP Piping Perhaps someone can find and post a similar link reviewing the NM.1 content.

I found the attached PDF at the location https://cstools.asme.org/csconnect/Filed...R8&43265.297581

Note that I've modified the PDF to shrink the file size to fit within the 2MB limit.

Thanks Michael & Dave for sharing. Hope this Code will be part of Caesar II package also.

Any other opinion is highly appreciated.

Warm Regards,