Repair of pipelines under crossings
Repair of pipelines under crossings
(OP)
I've got a peculiar situation which I would appreciate some input / experience.
We have a pretty thin (7.8mm) pipeline with a D/t of about 100, some 40yrs old with some identified corrosion defects under a road crossing.
Fairly uniquely in my experience, we are able to open cut the road to effect repairs as the owner is very reluctant to shut down and clear the pipeline to allow replacement / diversion.
The planned method was to use composite repairs on the multiple locations within the crossing where it requires it with some other non critical defects being subject to coating repair.
The picture is complicated by the pipe previously utilising a concrete sleeve which needs to be broken up to gain access to the pipe. We would like to then simply compact the back fill and do away with the casing or any other protective device (slab/half sleeve etc). According to API 1102, we're at the ragged edge (~0.95 of allowable stress) of acceptance, based on the original nominal wall thickness, even with a reduced MAOP from the original design.
My issues and concerns are:
1) API 1102 does not cover anything to do with defects to the pipe
2) With the number of repair sleeves in a relatively short section, I'm concerned about possible stress concentrations due to the additional loadings from the crossing
3) It is not clear whether composite types repairs, or indeed other repairs as listed in B 31.4, sec 451.6 are valid for crossings
My thoughts have swung towards recommending a single split sleeve with epoxy infill, but would greatly welcome thoughts and experience on the points above.
If you want any more info please ask, but I need to be circumspect in what I can put out there.
Thanks
LI
We have a pretty thin (7.8mm) pipeline with a D/t of about 100, some 40yrs old with some identified corrosion defects under a road crossing.
Fairly uniquely in my experience, we are able to open cut the road to effect repairs as the owner is very reluctant to shut down and clear the pipeline to allow replacement / diversion.
The planned method was to use composite repairs on the multiple locations within the crossing where it requires it with some other non critical defects being subject to coating repair.
The picture is complicated by the pipe previously utilising a concrete sleeve which needs to be broken up to gain access to the pipe. We would like to then simply compact the back fill and do away with the casing or any other protective device (slab/half sleeve etc). According to API 1102, we're at the ragged edge (~0.95 of allowable stress) of acceptance, based on the original nominal wall thickness, even with a reduced MAOP from the original design.
My issues and concerns are:
1) API 1102 does not cover anything to do with defects to the pipe
2) With the number of repair sleeves in a relatively short section, I'm concerned about possible stress concentrations due to the additional loadings from the crossing
3) It is not clear whether composite types repairs, or indeed other repairs as listed in B 31.4, sec 451.6 are valid for crossings
My thoughts have swung towards recommending a single split sleeve with epoxy infill, but would greatly welcome thoughts and experience on the points above.
If you want any more info please ask, but I need to be circumspect in what I can put out there.
Thanks
LI
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Also: If you get a response it's polite to respond to it.





RE: Repair of pipelines under crossings
Many areas now require no cut construction techniques such as HDD for a project like this. Based on the age of the pipeline, why ian't replacement instead of repair being evaluated?
RE: Repair of pipelines under crossings
I agree replacement is a better bet, but owner doesn't want to lose throughout.
What I'm trying to find out is if the normal repair options are still valid for crossings or not.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Repair of pipelines under crossings
Cyclic stresses and somewhat unknown loading conditions.
Are you happy with being on the ragged edge?
I think you know what to do.
If that was my pipeline, I'd be
1) making you case it, even though I would normally avoid casings, or
2) hottapping, blocking and diverting to a new crossing.
RE: Repair of pipelines under crossings
I do know what I'd like to do which is chop it and but a thicker pipe in, but client says no.
Next best is to close sleeve the whole thing.
The point of my question is to see if anyone out there has actually done anything similar (repairs under crossings in an uncased situation) or has any good pointers.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Repair of pipelines under crossings
No specific information or limitations are present for repairs under crossings, can use same repair type regardless of location in all the codes I see. I would not recommend clocksprings, given that I have seen installation go wrong, and these loosen over time. I would go for the split reinforcing or compression sleeve given that you will only have one opportunity to make a repair at this location and you want it to hold.
Not sure you are going to get enough stress concentration at the ends of these types of sleeves (fillet welded ends would be much worse), I guess it depends how much you think the ground & pipe will move in this area from the road traffic. I have made this type of repair under roads and used concrete slabs over top to distribute the load, with soil backfill/compaction requirements at the crossing. I have heard of modeling this scenario, doing FEA with sleeve configurations assuming you have enough info on the loading from the road crossing, but I have not done this type of assessment.
RE: Repair of pipelines under crossings
many thanks for the input - it more or less mirrors my current thinking. As soon as we take any of the defects if we took those as the min wt it fails 1102.
I hear what you say about the clock spring type repairs. the codes don't say anything, one way or the other about repairs under crossing, in part I guess because its rarely done?
The split sleeve is now under serious consideration, but practical issues and schedule are now coming into play.
I've seen FEA type work done on similar systems, but the time and cost is a lot more than just biting the bullet and replacing the thing. Compaction of the ground both above and below is reasonably straightforward, but the extra load during installation when the support isn't there is now starting to worry me. Short lengths mean a longer repair schedule. The road is a private one, but there are limits on how long they can have it open and financial penalties come into play if the repair takes too long.
It's not an easy one and if there are any more thoughts, please let me know.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
Typical.
For every problem there is an answer that is fast, cheap, and wrong.
= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube
RE: Repair of pipelines under crossings
When you say compression sleeve what exactly do you mean. I've got a fair idea, but I'm not clear how in practice you actually get The tightness that is required. I can't risk direct welding on this pipe.
Thanks for input so far to everyone.
I'm going to make a good play for replacement, but need to see what else is out there and how others have addressed this issue.
LI
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Repair of pipelines under crossings
http://www.ogj.com/articles/print/volume-99/issue-...
RE: Repair of pipelines under crossings
Is there any issue with SCF at the end of these sleeves if there is any bending stress?
Matthew
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Also: If you get a response it's polite to respond to it.
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
RE: Repair of pipelines under crossings
Sounds risky to me that you would try to break a conc. sleeve around a weakened pipe away from that pipe without doing any further damage to the weakened pipe. Someone is going to run a breaking hammer a little to hard or a little to deep, or actually pull a bulge in pipe as they pull/break a chunk of conc. away from the pipe.
Instead of a new conc. sleeve, or some other more elaborate casing to protect the repaired pipe, consider what is called lean conc. as a trench fill. It is basically a weak grade of conc. about 1000-1500 psi compressive strength. Strong enough to be a very good fill when it comes to distributing concentrated compressive loads on the pipe; weak enough so it can easily be broken out at a later time, and quite economical in ready-mix form vs. real, strong structural conc.
You guys know much more than I do about ASME & API pipe codes and what you can and can’t do under these conditions. I’d want to replace this section of pipe so I didn’t have to block the road again in a few years because we found another defect in the same deteriorated section of pipe. When you have a number of defects to repair in a fairly short distance I would wonder that you might not create a new defect in an only slightly less defective area right next to one of your fixes. I’ve seen this a number of times in both structural and mechanical systems, where you need to fix this two feet of something, and in the process the fairly weak next two foot section goes to hell during the process.