PVC Pipe

[fredt]

Can anyone point me to where I might get some design data for PVC pipe used as structural members. For example the torsional strength of cemented fitting joints. I can find general but limited data on material properties and plenty on pressure capability etc but not much about structures.

 

[MikeHalloran]

It doesn't do well as an air compressor receiver.

You are designing a structure that will never see sunlight? Or load?



Mike Halloran
Pembroke Pines, FL, USA

 

[fredt]

Mike
The application is mainly bathroom support appliances for the disabled. PVC tubing is currently used successfully for this application but we need to develop some loading rules for the non-engineer volunteer designers/makers. I can analyse structures using conventional methods including FEA but it seems to me (as a "steel" engineer) that the relatively complex behaviour of this material will necessitate a testing program. I would guess that someone somewhere has done it all before if I could track it down.

Creep is an issue so I can imagine it is no good as an air receiver but this isn't a big problem with non-continously applied load. Mostly there is no UV issue.

Regards Fred

 

[JStephen]

It shouldn't be too hard to load test it- build up a sample frame, put bricks on it till it breaks, etc- then you'll have the info you need.

 

[unclesyd]

You might look at the patio furniture business. There should be some guidelines that they use in case of a liability problem.

 

[MikeHalloran]

[It's no good as an air receiver because its properties fall off very rapidly with increasing temperature, and adiabatic compression heats the air.]

White PVC with cemented joints is used to build poolside furniture. I get the impression that the fittings are not regular plumbing fittings. So, yeah, somebody probably knows, but whether they've published is a different issue.

A Google search on /"PVC furniture" "fittings" / was modestly productive, indicating that neither tubing nor fittings used in furniture are the same as used in plumbing. I also saw lots of hits about 'high grade', 'sturdy', etc., but didn't find actual numbers.

Maybe that can get you started; somebody is making the fittings commercially. If you can get past the distribution chain, you might find an engineer with numbers.




Mike Halloran
Pembroke Pines, FL, USA

 

[fredt]

Thanks Mike and uncesyd. I have been pursuing those lines. The rapid decrease in properties is a consideration, even with hot bath/shower water. I have some data that suggests the tensile strength is halved at 110F compared with normal room temperature.

 

[stanier]

You need to understand that plastics are strain rate dependent. You will note that all properties to do with their strength are referred a rate of applied loading. If a load is applied rapidly you will get a very high response. If applied for a longer period the plastic can fail under a smaller load. Hence manufacturers use the tests that put their products in a good light. The data may not be applicable to your needs.

Suggested reading:

Plastic porduct Design and Process Engineering by Harold Belofsky
Plastics Microstructure and Engineeering Applications by Mills
Fracture Mechanics books by Hertberg
Failure of Materials in Mechanical Design by Collins

Most plastic pipe manufacturers will have tested their solvent or adhesive joints. Once they prove the mechanical strength is greater than the parent pipe material they stop the test. The loads on piping are not synonamous with that of a piece of furniture. You will have to do you own design and testing if you are to avoid the risks.

 

[fredt]

Thanks stanier
These are good references and I appreciate the advice re. properties.

 

[arto]

The stuff gets brittle with cold too. On scout winter freezeouts you sometimes see nice PVC dogsleds on saturday morning & shattered pieces of scrap sunday morning