Underground Pipe repair

[njames024]

I am looking at repairing some underground 3" (200F 50 psig design/ 125F 25 psig operating). The pipes don't see a ton of flow (I am not able to give an exact number), and one goes under the slab and straight across, the other has 2 elbows before coming up through the slab. We are trying to repair the pipes without digging up the slab. The reason for the replacement is FAC, localized corrosion in places and it has been determined something needs to be down during the next shutdown. One of my fellow employees who I'm working with is going to BPIG next week and will inquire about what some other engineers have been successful doing. I figured I would ask on here if anyone has any experience on here that would help.

 

[DekDee]

njames,
Not an expert but I know the first thing any knowledgable engineer is going to ask is what is flowing through your pipes - makes a huge difference on any advice they may give,
Regards,
DD

 

[Duwe6]

FAC will be at the ells, or in the pipe immediatly past the ell; or both. If a repair is necessary, saw out that portion of the slab and replace that section entirely, using a prefabricated piece.

Keep in mind that for 100 psi in a 3NPS pipe, the required minimum thickness is only 0.010"*. Are you sure that a repair is necessary?

*assumes proper bedding during backfill, thus no outside stress and line being fully supported.

 

[njames024]

Water is flowing through the pipes sorry I forgot to mention it. The repair is definitely necessary and will be done because of potential "environmental concerns" with water leaking from these pipes. I was hoping for options other than replacing the pipe where it sits, as it is 5 feet underground would require a substantial sized hole dug in our building. The pipe runs right through the main walkway of the building.

 

[bimr]

You don't have the complete picture in your post. If there will be a large expense or disruption, you might consider directionally drilling a new pipe.

You might also consider abandoning the pipe and replacing it with a piping on different route through the building.

 

[njames024]

Directionally drilling a new pipe?
And we are considering abandoning the pipe in place and replacing the pipe through a different route. It has been determined that the pipe must go across the walkway to the return, tying the pipe into other existing pipe that does that is not an option. I am looking mostly for information if anyone has done any pipe lining similiar to epoxy or CIPP?

If there is anything else I need to post to give you the complete picture let me know...

 

[bimr]

One needs to know the scope of the work. Is it 10 feet or 500?

Your pipe size of 3-Inch is probably too small for CIPP. CIPP is typically done with 6-Inch minimum pipe size.

Pipe lining with epoxy has been done. The greatest determinant of success or failure is the training and experience of the applicator crew. There are limited methods to test an application and no options to mitigate application failures, except for pipe replacement. Epoxy is a remarkable substance and it is assumed that it can be applied correctly, but the cost of epoxy installation may equal or exceed the cost of replacement.

 

[njames024]

The run of pipe is approximately 45'. Sections range from 3-5' below the top of the slab. The slab is 8-12".

 

[Duwe6]

"Directionally drilling a new pipe?" Yup.

 

[njames024]

I'm unfamiliar with this... link please?

I'm not sure what the limitations would be but we have 2 sets of rebar in our slab (2" from top and 2" from the bottom) and they are spaced 12" apart, running both N/S and E/W. My guess is we would have to manage to avoid the rebar not sure if that is possible...

 

[bimr]

You will need a place to set up the drill rig and a place to pull/push the pipe back. The pipe would be installed 3-5 feet below grade. You would still have to break through the concrete to bring the pipe through the floor.

Not sure if it is feasible, it will depend on the site particulars. A HDD Contractor would probably do a project of 45 feet. You would have to have the HDD Contractor walk through the project to see if it is feasible. The cost for HDD is around $20/ft plus set up.

Many municipalities now require directional drilling under roads to avoid and minimize excavation and repair of the roads.

Here is what HDD looks like:

http://www.youtube.com/watch?v=w6j8dFo-0lk

 

[LittleInch]

njames,

Maybe not for us, but for any company to give you a properly informed decision you're going to need to let them know:

plan and section of your piping or isometric
how much room you have available at any cut locations
fluid being transported
flow rate - "don't see a ton of flow" is so vague it's not worth talking about
acceptable pressure drop across your section
Radius and types of elbows - can you replace with larger radius bends??

Then options will be able to be identified and issues determined. 3" is a bit small to repair / insert liners or flexibles and the loss of ID will be significant, hence the pressure drop question. Also access space and difficulty navigating elbows is crucial to whether some techniques will work or not work.

your options would seem to be a liner / flexible of some sort or a spray on epoxy. None are cheap and many have issues, but without the info above, you won't get much further.

Drilling laser guided new holes sounds like the best plan to me....


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