GRE/HDPE Piping Stress Analysis

[StrugglingEngineer]

Dear All Piping and Stress Engineers,

Im currently designing an underground piping system of Firewater Network for an Oil and Gas Refinery, and their requirement is to use either GRE or HDPE pipe for it. I am stuck on the last part of selecting either this piping system shall be Stress Analyzed or not. API SPEC 15LE does not specify directly.

Need to know criteria of Stress Analysis of Piping System, a reference of code, standard or any Design Engineering Practice or any Best Practice of a renowned Refinery will be helpful as a reference or as a go-by.

 

[HTURKAK]

I will not suggest the use of GRE or HDPE pipe for fire loop and strongly advise the use of steel or DI pipe.
If you want to design the GRE or HDPE piping, you may look to
-AWWA MANUAL M55 PE Pipe - Design and Installation ,
-AWWA MANUAL M45 Fiberglass Pipe Design,
- Manufacturer's standards

Good luck...

 

[StrugglingEngineer]

Hi HTURKAK,

I really appreciate your concern, but its the requirement of the Company, and I looked it up alot of Refineries around the world uses HDPE piping for FW.

Also, Thanks for sharing the standards. I will surely look them up.

 

[LittleInch]

I would definitely stress GRE piping which can be undertaken using ASME B 31.3. GRE has a high Poisson ratio and under pressure usually contracts. It is also fairly stiff and hence can generate large stresses at elbows and tees.

HDPE on the other hand (or PE100 as it is mainly called now), is very flexible, has a tendency to creep under sustained load, and unless you're subjecting it to large temperature deviations, doesn't expand very much.

Bothe systems are usually pretty good for buried networks, but not good for above ground exposed sections.

If you haven't already, look up the NFPA specs (free to view online) on these systems which limit the above ground systems and those parts potentially exposed to heat and flames themselves to Iron or steel pipework.

ANYTHING to do with fire systems needs to be approved by the AHJ (Authority Having Jurisdiction) in whatever location or country you're working in and THEY need to be happy to use PE or GRE. It doesn't matter what the company says, the AHJ trumps everyone. So you need to find out or ask the question - is the AHJ happy with this? if they are fine, but I would start with NFPA requirements and work from there. Your Technical Safety engineer should know.

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

 

[MJCronin]

Struggling ....

LittleInch yet again gives very good advice when he says:

ANYTHING to do with fire systems needs to be approved by the AHJ (Authority Having Jurisdiction) in whatever location or country you're working in and THEY need to be happy to use PE or GRE. It doesn't matter what the company says, the AHJ trumps everyone. So you need to find out or ask the question - is the AHJ happy with this? if they are fine, but I would start with NFPA requirements and work from there. Your Technical Safety engineer should know.


I have repeatedly seen rat-weasel clients back down from their own Standards as well as project scope when challenged by the AHJ !! .... When questioned the client will say something like [i]"Well I wanted the Pipe Stress/Design Engineer to confirm my material choice ... Nothing should be built that the Authorities will not permit !!"[/i]

Some other information you might need, besides confirmation of the proper material is the need for a detailed stress analysis of the underground system. There are many many systems out there which have been designed, installed and operated without a detailed stress analysis.

If you must perform a detailed analysis, CAESAR-II has the methodologies and features to handle both underground and non-metallic piping systems.

Keep us in the loop about your final decisions

Regards

MJCronin
Sr. Process Engineer

 

[MickMc]

I am not a stress engineer but can tell you in Middle East Projects which I have been working on in Client side in recent years use of non metallic piping for water systems including FW is common. Most of my experience is with GRE but current project is HDPE which is underground only due to limitation on temperature as Solar Radiation is considered at 87°C which is too high for HDPE.

What is common in these projects is that we as Client stipulate that Stress Analysis be carried by vendor with stress isometrics provided by contractor and also that vendor provide supervisors during installation.

 

[GC_Hopi]

It does depend on the AHJ but the OP may have an industry exemption so maybe the oil/gas client is the AHJ. Below is a snip regarding NFPA 24. I would be sure to document the client's decision in case you have to do a redesign. The documentation will help you with getting additional fee for the redesign if you have to go down that road.