I'm running an FRP wastewater line per BS 7159. Question is, how do I treat the "rigids"? Meaning, usually with steel pipe I'll define a weld neck flange (or a flange pair, or a valve with flanges...etc.) as a "rigid" with a defined weight. Do I do the same thing for the FRP flanges and the steel valves? Can a flange pair be considered as "rigid?" How do I treat these?

Thanks,
Kelly

Hmm a good question, I think you know your answerr to this already....

CAESAR II has always looked at "rigids" as being those items which are appreciably stiffer than the pipe. So Valves Flanges etc. are more "ridgid" hence CAESAR II using the rigid elements.

So I ask you if you took the two ends of a FRP flange and tried to bend them a fixed amount and then do the same for the matching pipe would their Krate be much more stiffer than the pipe? My guess would be yes....

I think there are other considerations for FRP pipe than the stiffness of the flanges, although John L. is surely right that the FRP flanges are "rigids" when compared to the FRP pipe itself.

1. Steel and Cast Iron valves are going to be more rigid than FRP "rigids." This may or may not be a significant factor in your analysis. It may be sufficient to change the material for the valves and then change back to FRP to continue.

2. Mechanical joints are going to have some inherent flexibility due to their construction, although the joints themselves may well be modeled as "rigids." The FRP vendor should be able to provide guidance.

3. Wrapped butt joints will be more rigid than the pipe, but perhaps not enough to consider them to be "rigids." Again, the FRRP vendor should be able to help.

4. FRP tees and elbows may well be best modeled as "rigids." I hate to repeat myself, but the FRP vendor should be able to give you good advice here too.

Summary:

Call your FRP vendor, or several of the vendors on the bidders' list. If they are prospective bidders, they are going to be eager to help for the good will (you, after all, are going to be doing the tech eval). If there is a supply contract in place, the successful bidder still has self-interest in helping you - if you call and ask for advice, and document the phone call, he will be up a tree if something goes wrong later.

Most of the major FRP vendors have different construction details for a lot of their pieces and parts. It's not really possible for someone to give specific advice on how to model "FRP pipe" without knowing who the vendor is and what particular resins, joints, and winding details are specified. For some vendors, such as Ameron, even the nominal pipe diameter is relevant to the issue. You may have to model 4" flanged joints differently than 24" ones.

As has been repeated may times by the grizzled veterans here, there are many possible answers to most piping problems. I would expect you to have to spend several hours with a phone at your ear to get the details you need. It would scare hell out of me if someone like me gave you specific answers to these questions as you have posed them AND I KNEW YOU TOOK THAT ADVICE AND RAN WITH IT.

Since you have posed your problem in intelligent terms, I suspect you will be able to do the right thing with the information you eventually assemble. But your taking generic advice for FRP piping is a hell of a lot more hazardous to your professional health than my taking generic prescription drugs is to my physical health.

Sorry if my answer makes you overrun your budget.

Yes.... My point was that the use of rigid is all relative to the pipe section. And it is certainly judgemental as well, but lets look at this subject in this regard... The more rigid components that are in an analysis model the higher the displacement stresses will be. Therefore more rigids rather than less MAY (??) be a safer way to go certainly in so far as equipment reactions would be concerned!


And don't forget to add a picture to the picture thread!

Good Luck with this because it does have a lot of "ick" to it!

Thanks for the advice...and as always, I take the advice given on these boards under advisement only. I would never take something as being the "last word," I would only add it to my knowledge base. Take it and pass it through the gray matter, as it is.

These are basically butt-wrapped stub end flanges, which I suppose are commonly used in FRP systems. I have tried to contact the manufacturer, but to no avail. They are in Canada and are somewhat hard to get in touch with...but I will keep trying!

You're right Mr. Luf...the "ick" factor is high on this one. Thanks again, I'll keep doing my homework.