If you're asking for a manufacturer's allowable figure, that would be zero.
If you're observing movement during testing, you'll learn that maximum in due course. The pipe should be secured prior to testing. Then in the real world things move under pressure- if it holds it holds
While I'm not sure a responsible manufacturer would claim absolutely no movement, do you know why and how much this particular joint "slip(ped)" out? [I'm not sure there can be much confidence, long-term in the pvc pipe installation until this question is satisfactorily answered.]
Even if you use thrust blocks when installing c900 blue piping you must use retainer glands with threaded rods at each joint.
As the rest of the guys mentioned no matter what the manufacturer claims pipe will always move under pressure unless is threaded.
I guess there is really not yet enough information given to know why this incident has occurred. There are however many potential reasons for movements in pipelines, and maybe particularly so in the case of plastic pipelines. However, when it comes to handling loads imposed on pipe material over a significant duration of time, it should be understood plastics have a very low long-term modulus and a very high long-term Poisson’s ratio. Considering responses of the pipe to applied pressure and other loads involving these specific properties, and also an understanding that thermal expansion/contraction coefficients are many times that of metal pipes (e.g. see footnotes to table on page 17-23 at
etc.), and there can be a surprising amount of apparent movement to contend with, even without considering other unintentional thrust movements of pipes (such a bucking sideways due to inadequate weight, or soil support, or movement of valves, anchorages or thrust blocks etc.)
In a recent presentation I believe I heard an expert in polyethylene pipes claim that an originally 20 feet long stick of DR 21 pvc pipe (I guess pressurized in kind of short-term fashion to its current/liberalized pressure rating of 200 psi) would shrink in axial length due to Poisson effect of pressure alone about ½ inch (this perhaps thrown out there to somewhat sort of blunt in advance concerns of even more pronounced tendency to shrink of polyethylene pipes?) While I guess some thermal movements could be as much or more, it would appear that in even a long, reasonably straight run of just Reiber-gasketed pvc piping, Poisson effect alone would appear (if one looked closely/carefully enough) as at least a small “slip” in the joints. That is why I was skeptical of the claim of “no movement”.
In thinking about this I guess I probably should have elaborated a little more about the Poisson cylinder calculation result as it relates to what I called “short-term” pressurization. What this means is that if you held the pressure on for a very long period of time, the axial contraction for an individual pvc pipe section could be far more than even that initial ½ inch value (due to a marked reduction some authorities say from an initial modulus of say 400,000 psi for upvc to a long-term modulus for same that might be as low say as 140,000 psi, and there is also generally an apparent increase in Poisson’s ratio µ also for many plastics). The net result of both these effects, if long-term, would appear to be a disproportionate/far greater decrease in axial length of a pressurized plastic cylinder just between gaskets in a straight pvc pipeline, due to the fact that reportedly µ shows up in the numerator of the DL equation and modulus in the denominator.
That being said, notice also the quote many years ago from the manager of the Johns-Manville research lab mentioned also in the prior thread at
that indicates perhaps non-obvious axial movement may even occur with very short duration higher pressure spikes, “Since PVC pipe moves axially as well as circumferentially in response to pressure surges ("Poisson's ratio effect"), pipe may undergo scratching of the outside when buried and in contact with sharp stones in the backfill. This area requires further study."
All of this nevertheless does not appear supportive of a “no movement” claim.
