HDPE pipe branch connecting to CI pipe
HDPE pipe branch connecting to CI pipe
(OP)
Hello,
I am designing a new 125 OD SDR11 pipe connecting via a tee to an existing 150 dia CI pipe. The test pressure will be 10 bar. The pipe supplies potable water from a borehole site, so temperature variations would be small - say 5 degrees C. I have a problem understanding what will be the combined effect of the thrust at the tee, the Poisson force and any thermal movement. I can't work out what restraint is needed to protect the CI pipe joints and what pressure rating should the joint between the HDPE pipe and the tee be.
Can anyone help by pointing me to a design guidance document or in any other way?
Many thanks in advance.
I am designing a new 125 OD SDR11 pipe connecting via a tee to an existing 150 dia CI pipe. The test pressure will be 10 bar. The pipe supplies potable water from a borehole site, so temperature variations would be small - say 5 degrees C. I have a problem understanding what will be the combined effect of the thrust at the tee, the Poisson force and any thermal movement. I can't work out what restraint is needed to protect the CI pipe joints and what pressure rating should the joint between the HDPE pipe and the tee be.
Can anyone help by pointing me to a design guidance document or in any other way?
Many thanks in advance.





RE: HDPE pipe branch connecting to CI pipe
Yours however may have a sort of twist so to speak - while you do not say in which direction you are approaching the tee, I am guessing you are to be approaching at right angle the larger exisiting main (i.e. into the "branch", not the "run").
Is the cast iron tee existing, or are you tapping or cutting in a new one etc.? (If the latter, I guess it would be helpful to know the actual outside diameter of the old cast iron.) If the former, it would be helpful to know the specific type of joints involved with those items. In any case, while I suspect the forces will not be real large with such small pipes, it certainly won't hurt to have a "plan". Like others who have not reponded, will wait on alittl more info.
RE: HDPE pipe branch connecting to CI pipe
https://plasticpipe.org/pdf/chapter07.pdf
RE: HDPE pipe branch connecting to CI pipe
Any expansion or contraction of the PE pipe will make the joints of the existing pipe pull off, so I want to make sure it is restrained from movement. But the question is - what force and in what direction should be restrained? Is it the thrust + thermal expansion force - the poisson force?
Also, what pressure does the connecting flange need to be rated to? I think this needs to be the higher of the thrust or shrinkage force, but there are opinions that it should be the sum of them.
Thanks again
RE: HDPE pipe branch connecting to CI pipe
RE: HDPE pipe branch connecting to CI pipe
While 6" gray cast iron piping in good shape may be a more robust system than feared, and the aggregate and perhaps even somewhat rebating thrusts from 4" hdpe might not be large, you are nevertheless prudent to think about same and maybe also one could put a thrust collar and wall of some sort on the new 4" hdpe branch line not far from the tee. If that sort of thing is not available with your hdpe, I guess a section of 4" ductile iron pipe with (I know available) thrust collar could be restrained to the tee branch, and work with/inside a small transverse concrete wall/anchor, thereby at least isolating all hdpe effects. Since you are already cutting into the old 6" line, there are perhaps other options, e.g. removing some of that as well and replacing with new/modern 6" jointing and/or even stronger modern piping for some distance in the run directions etc.
RE: HDPE pipe branch connecting to CI pipe
https://plasticpipe.org/pdf/chapter15.pdf