Movement of Buried Water Piping
Movement of Buried Water Piping
(OP)
At my plant we have underground raw water piping. The original piping is ductile iron. At one area the 24" header connects to a valve and then a reducer connects the other side of the valve to a 12" header. Several months ago we replaced the original 12" header with HDPE pipe. The HDPE pipe is connected to the valve via the 24x12 reducer and mechanical joints. Earlier this week we a had leak that pushed up through 10 feet of ground. Excavation revealed a leak at the mechanical joint where 24" side of the reducer connects to the valve. There are rods the travel the length of the original 24" ductile iron pipe and are welded to the valve body and then to the 12" flange. The rods broke away from the 12" flange. Some folks think the HDPE pipe moved a few inches away from the valve, causing the mechanical joint to unseat itself. I am wondering if the mechanical joint simply had a leak that, over the course of a few months, washed the soil away from it and cause the pipe to sag. Not sure.
Has anyone had any experience with underground piping moving? The water system didn't experience any sudden pressure increases. Pressure was normal and then dropped quickly.
We are in the process of excavating the entire HDPE line to check for any movement of the pipe, thrust block, etc.
Has anyone had any experience with underground piping moving? The water system didn't experience any sudden pressure increases. Pressure was normal and then dropped quickly.
We are in the process of excavating the entire HDPE line to check for any movement of the pipe, thrust block, etc.





RE: Movement of Buried Water Piping
Only put off until tomorrow what you are willing to die having left undone. - Pablo Picasso
RE: Movement of Buried Water Piping
I still think this joint was leaking and eventually let loose. The pipe is about 10 foot underground and the water shot several feet up above the ground level.
RE: Movement of Buried Water Piping
RE: Movement of Buried Water Piping
The other thing I wonder about is the inside diameter of the HDPE piping. My facility replaces a lot of old steel piping with HDPE of the same OD, we don't always account for the smaller ID. I wonder if the smaller ID of the 12" HDPE line could be causing a higher pressure at the valve. I wouldn't think the higher pressure would be enough to cause joint failure unless the joint was not properly assembled.
RE: Movement of Buried Water Piping
RE: Movement of Buried Water Piping
1. Pronounced "Poisson" effect of plastics, and particular in long-term (a straight run of pipe not subjected to other tensile forces shortens, or tries to shorten, significantly when pressure is applied)
2. If the hdpe pipeline was warmed by sun or installed in warm weather, and then at some point water is eventually introduced cooler than that installation level, there is a pronounced thermal shortening, or attempted shortening of plastics.
[As I believe Mr. BigInch indicated, the forces that are applied, however, would be obviated at least some by the soil pressures and friction at 10 feet of cover.]
RE: Movement of Buried Water Piping