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Underground PVC Isolation Options

Underground PVC Isolation Options

Underground PVC Isolation Options

Today I was asked how we can positively isolate a section of underground 3" schedule 80 PVC pipe from an outfall pond. The isolation is needed to install a new valve/break in the line to connect to the new carbon steel pipe in the basement pump house. They want to change the connection point to outside of the pump house so if the PVC cracks as it has in the past, it won't be in a hard area to work with.

My first consideration was if we had access to the end of the pipe in the pond to just put a temporary cap on it and stop flow entirely. This was shot down because the end of the pipe is 10 ft into the pond buried under muck.

My second thought was that we'd have enough time to cut the pipe and put a cap on in the excavated area, put the spool together and connect both ends. This doesn't look good either as the flow could be too much and the concern of washout or collapsing the trench ended that.

The PM recommended we freeze the PVC and isolate that way. I have not seen a freezing isolation, and never heard of it being done on PVC. This sounded like a bad idea with the potential to crack, but with few options, it may be our best one.

Are there any recommendations of how to isolate PVC in this situation? Is freezing actually a good route?

Mechanical Integrity Specialist (Year 1)

RE: Underground PVC Isolation Options

Errr "ten feet into the pond and buried in muck"??? So how is there any flow in the pipe? Doesn't make sense.

Freezing might work if its done slowly and the external temp is not < say -10C. But needs zero flow, clean water and a contingency in case you crack the pipe. I would practice on a spare bit of pipe myself.

Is there any access to the pipe ends at all?

Have you got a sketch you can post with elevations, pressures, valves etc

PVC is a horrible material though, might be cheaper and easier to replace the whole thing in PE.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Underground PVC Isolation Options

Sketch attached. It would be 10' in distance from the edge of the pond to the end of the pipe, not depth..

The muck isn't exactly burying the pipe, just covering it considerably.. The muck/solids are sent to an area refinery to be composted or broken down.

I don't deal with this pond very often at all so to say the water is clean with the muck is highly unlikely. Zero flow can be accomplished.

The pipe end we have access to is the end we are modifying and if opened, would be pushing the pond water in our faces.

PVC is the worst! never seems to last and always has issues fitting to pumps, tanks, etc..

Mechanical Integrity Specialist (Year 1)

RE: Underground PVC Isolation Options

Well if the water is that dirty / polluted there is a good chance your ice plug won't hold, but I guess the depth of the water is only 5 or 6 feet?

I think your options are kind of limited, but can be either drain the pond / gulley suck / pump it somewhere to get access to the pipe end.
Send a diver down with a pipe plug
Build a new line
Connect a tap to the pipe just outside the wall and pump fresh clean water back into the pond to allow your freeze plug to work but if the pipe is under any sort of stress you risk it fracturing.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Underground PVC Isolation Options

I figured my options were few. I had thought that finding the end of the pipe and throwing a cap on was a decent plan but received a heavy glaze when I mentioned it. I get no one wants to get into an industrial run off pond but how is freezing a 15 year old PVC line any better? Draining the pond would be the smartest but I don't know if we can get it low enough.

Mechanical Integrity Specialist (Year 1)

RE: Underground PVC Isolation Options

How deep is this buried?

If you connect a valved tee using a bolted connection and extend the pipe up to higher than the same level as the pond you should be able to insert an inflatable balloon down into the pipe then inflate it to seal the pipe.

You would need as big a connection as possible.

Worth looking at?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Underground PVC Isolation Options

Well, maybe you need some kind of line stop arrangement.

Maybe you can find a service or rent the equipment?



The problem with sloppy work is that the supply FAR EXCEEDS the demand

RE: Underground PVC Isolation Options

I think what we may end up doing is replacing the line. Rerouting is a little undesirable because of the prefabbed carbon steel spools but I'm thinking if we hydro and get something to yank it out of there we can probably get a new pipe put in without getting too terribly wet. I don't know if the pond will backfeed down the trench but even then we can put temporary barriers up to fix that..

Mechanical Integrity Specialist (Year 1)

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