72" Pipe Repair at 45deg Miter bend

[dnigos]

All,

Data: 72" CS line, Low Pressure (~20psig) in water service.

I'm stuck here. I have a leak at a 45° miter bend weld. Entire weld was previously composite wrapped don't know when, but I believe the wrap just failed. How would you fix it?

Here's my options and thoughts:
1. Utilize another composite wrap. This means, I'll have to remove the existing wrap. The problem with that is, I'm probably going to uncover more damage than good.

2. Welded box. BIG BIG BIG.

3. Cut and weld a new 72" miter bend. BIG BIG BIG.

I'm fishing for other options here. I do not have much experience in this field, so any advice is greatly appreciated.

Thanks!!

 

[BigInch]

Uncover and inspect. Then see if you can rewrap. If not consider options 2 and 3. Sleeves don't fit miter joints very well, so...

What's the advantage of a box? Very bad even for low pressure containment. Needs very very thick walls and lots of reinforcement plate and they are still not a very reliable.

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[chief]

Old seamans trick was to build a cement box around the leak. Gives you time to consider a more permanent repair.

Offshore Engineering&Design

 

[chicopee]

Also determine cause of leak( stress at miter, corossion, erossion inside the miter, soil and traffic loading if buried) for that more permanent repair mentioned by Chief. I like that cement box temp. repair idea. Old seamans have a lot of tricks up their sleeves because when at seas that is all you may have.

 

[rconner]

Was just curious could the existing wrap be some form or original coating for the pipe line (e.g. like an AWWA C203 coal tar-type system), or is the fitting only just locally wrapped (e.g. like it was repairing a prior leak in this miter-welded fitting area)? Also, do you know anything about the soils, any internal lining system in the pipe, and is the line under any form of cathodic protection?

In any case, if the leak is e.g. a corrosion hole I wonder if it might be possible at least for a temporary repair to drive a wooden plug into the hole (e.g. see

http://www.pollardwater.com/pages_product/wooden_plugs.asp),

cut it off reasonably close, then weld some sort of shaped plate in place over that? If it is a corrosion hole and the line is not cathoidically protected, maybe you could buy at least some more time by then hanging an anode or two on the fitting and covering the area with e.g. a new "shrink sleeve"?

While I guess something like that might even conceivably be done under pressure if the pipe is reasonably sound, it would probably be safest to remove pressure if that is at all possible -- whatever you do, please do it safely, particularly if you don't know the integrity state of the pipe/weld as that is big pipe (and a "lotta wotta")!

 

[chicopee]

I am also questioning the wisdom of a mitered joint.

 

[BigInch]

Why?

"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization

 

[dnigos]

I appreciate all the input guys!!

BigInch: I'm leaning on that route more and more...since my options are very limited. We should be able to remove the existing wrap and rewrap without having too much of a problem. There's no advantage in a box. It was just an option.

chief/chicopee: At this point, I'm assuming the cause of the leak is due to a bad miter weld and a failed wrap. There's not a lot of records on this pipe, but I'm guessing the wrap was installed about 10 years ago or so. The cement box idea was not considered because of its lack of flexibility. Currently, the ground supporting the pipe shifts every now and then, causing the pipe to bend/buckling. Composite wrap would have a little more (but not much) flexibility than cement.

rconner: the pipe has no coating (besides the paint). The wrap was used to locally repair an assumed to be a bad weld at the miter.

Thanks guys!! If there's more comment.....keep 'em coming.
Dex

 

[MikeHalloran]

Uh, the >ground shifts under the pipe occasionally<, and presumably under whatever is supporting the miter's branches, and you expect it to _not_ leak/fail when that happens?

I think you need to get a geotechnical engineer to take a good look at your supports and whatever is/isn't under them, and provide better support or build more flexibility into the pipe >system<.



Mike Halloran
Pembroke Pines, FL, USA

 

[chief]

If unable to isolate water flow, plug the leak with a wood plug.
Take a section of 3" pipe and slice it in half along its length.Tack weld the half slice around the pipe to form it, using heat and hammer, edclosing the original weld joint. When formed around the pipe, complete welding of half slice along its length and where joints meet.


Offshore Engineering&Design

 

[chicopee]

why? Well the result speaks for itself. Would have been better to have an elbow.

 

[rmw]

Can you get access inside the pipe. If so, there are epoxy coatings that you can dope it with but you have to be able to get it clean to apply the epoxy.

rmw