Exceeding Temperature Rating of PVC Piping

[etcm]

Recircing a well insulated chill water loop recently overnight resulted in loop temperature at 170 degrees F at probably 50-75 psi in a ten inch PVC pipe (part Schedule80 other part, 1120 sdr-26). It exceeded the 140 temp limit and even the 167 degree plastic point, and the piping bulged out and distorted (oval-egg shaped on the end of the pipe) at a Dresser coupling (to a steel pipe section) and at a separate flange. Does anyone know if there are any available thumbrules for estimating the suitability for service of this piping?

We are excavating now but I question whether the entire piping system must be replaced even in sections that have no readily visible distortion?
Thanks,
etcm

 

[ClydeMule]

I believe the pressure ratings are @ 70F. If you are going to use PVC you will have to have some kind of temp actuated shut down if you are close to the pressure ratings.

THe fact that it is chilled water piping doesn't mean that it can run hot as you found out the hard way.

This happens in Agricultural installation a lot. People dead head irrigation pumps and wonder why the 3" pipe is now 6"

Clyde

 

[ChasBean1]

I've never seen a PVC chilled water system, but I also haven't seen a chilled water system reach 170°F. It must be really well insulated - seems like equilibrium would occur at a much lower temperature. I would replace the entire system with schedule 40 steel or copper (L type or thicker).

 

[etcm]

Thanks for the input, interesting though. The site this is at is an agriculture dept. site and the recommended fix from my contractor is steel! Both of you hit it (sort of) on the head. The reason the temp got up so high was a 125kw motor recircing a 10", about 65 foot loop, with the recirc valve open. It was highly insulated....underground too! Almost every elbow and flange distorted (ballooned out) with numerous leaks. Amazing that we did not burn the pump up too.
Thanks,
etcm

 

[ChasBean1]

etcm: Replace the pipe but don't forget about resolving whatever caused this. CHW system should not reach 170° regardless of what type of pipe. Good luck, -CB