4C900 PVC Pipe Buckling during Testing

[ulloap]

Hi Gents,
I’m a machinery designer for the PVC Pipe Industry, few months ago I was involved to design a Hydrostatic Pipe Tester according to AWWA C900/5 or FM Standard. One of the special features requested by my customer was “Quick-Burst” capability using a whole pipe -6.1m / 20ft long- as a sample instead of using short pipe samples as the standard said.
The machine is capable to test from 4C900 to 12C900, and hasn’t any problem performing Hydrostatic regular test or quick-burst test -according to the DR- in all the size from 6C900 up to 12C900
Few weeks ago I was testing 4C900 DR18 at quick burst pressures -740 psi- during time required by the standard -60sec-and something strange to me started happening, the pipe itself buckled…as you shown below.
As a mechanical engineer I’m trying to relate the behavior of the pipe itself with Euler Column Effect, with no much success…
What I’m to intent is to simulate by FEA what’s happening, I don’t know exactly if I’m clamping too much the pipe or maybe I’m adding extra support “points” to it….

Do you guys have seen this kind of buckling before on a pvc pipe during a test?
Any suggestion will be helpful!
Regards
LPUS

http://files.engineering.com/getfil...d715-4082-bbb4-77e575c82bc1&file=IMG_3224.JPG

http://files.engineering.com/getfil...b77d-41cd-8e29-f3131b1b93ea&file=IMG_3228.JPG

http://files.engineering.com/getfil...b20-bada-c1702d8c5daa&file=IMG_3213_(002).jpg

 

[itsmoked]

Links above to 4x larger images.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[EdStainless]

Are the ends restrained? I would suspect that has and effect.
In metal tubing people will sometimes clamp against the ends, in high pressure tests this causes very strange failures as the tube length will change with applied pressure.

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P.E. Metallurgy, Plymouth Tube

 

[racookpe1978]

I will second the "fixed ends" causing a axial thrust theory -> That led to a buckling failure at the weakest point. Were you pushing the two end covers onto the pipe to maintain pressure and prevent leaks?
Do you normally test larger diameter or smaller diameter pipes at this length?
Have you tested this diameter pipe before at this wall thickness at this length?

The pipe buckled "up" (lifted up off of the supports). Was that it's failure position, or did it rotate or move after the failure and before the picture? Did it fail in place, then lift up as the water was drained and weight removed?

 

[Artisi]

I'll third the "fixed ends" as the problem.


It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)