Plastic Deformation of Piping due to Ice 2

[AKInspector]

Can someone give me guidance on how to go about evaluating piping that has swollen due to frozen water/product inside? I cannot find any black and white criteria for acceptance. Obviously, best practice is to cut it out and replace the deformed section. Is there a method out there to evaluate this type of damage?

API does not address this at all.

 

[vesselguy]

AkInspector,

And you won't find any standard that will address your issue. Seriously, if you can see that the pipe is "swollen", then it has obviously yielded and can't be put back into service. There is nothing to evaluate here.

Also, all valves that were part of this frozen line is probably all messed up and you got to get them out to valve shop to check them out. Likely they are garbage as well. The company I work for had exactly the same stupid thing happend to them 2 years ago. Some people did not empty the line after leak testing in the winter and the whole darn system froze. All valves were screwed. Some lines had to be replaced.

Also, check out this notice by ABSA on this issue.

http://absa.ca/IBIndex/ib04-003.pdf

 

[AKInspector]

Vesselguy-

I aree with you on putting equipment out of service that has yielded. But is a material automatically considered worthless if it yields? There are standards for bends in piping and tubing, and if pipe or tube is bent, it has yielded, right?

Anyway, we agree that the damaged material should be taken out of service. Even if there is no black and white standard covering this, there should be. When I worked as a welder, there were more than a few times I had to repair low(er) pressure water lines by heating the pipe, hammering the ruptured area to close up the crack, and welding it shut. Those lines are still in service, and I'll bet the operators have no clue about the repaired areas now. What happeds when someone decides to bump up the pressure to MAWP?

If there was a standard, ("SHALL" vs "should" or silence)those ruptures would have had to have been cut out and fixed right.

 

[Bonswa]

If you want, you can ring gauge this piping as if it were heater tubes. Use the same level of acceptance that you would for those tubes. it's either "go" or "no go". that's it.

I recommend hydrotesting that entire line when you're finished with the repairs. You may want to do some spot RT on some of the welds that you're going to keep.

 

[vesselguy]

AKinspector,
I know what you're getting at with what you're saying. Yes, of course the material has to yield to form the elbow, but an elbow is carefully deformed and the material is heat treated afterward to remove cold working (in the case of a cold formed elbow). Yes, there is some strain hardening caused by the plastic deformation and could infact make the part stronger, but it may well be at risk when used in low temp service or other corosive environment due to the increased hardness in the material. You can't compare a carefully formed part with a deformed part caused by service; its NO comparison.

Yeah, OK I'd buy in on your statement about fixing a blown water line that you did many moons ago. There no harm in leaking water as long as you don't happen to be right at the burst seam when she blows. But you do that stuff in a petro-chemical plant, stuff will flow down on you. LOL

 

[fortmceng]

On a pipe which has bulge, there would location of high stress concentration on either side where the bulge ends. These points would tend to yeild and could initiate crack under load/stress (on a pipe it would form cracks in the longitudinal direction). Again all this would depend on how much stress you apply. It is very difficult to analyze those high stress areas without using advanced techniques like FEA.

A pipe which has not failed even after having a bulge is all because piping codes provide a good safety factor. I don't think it is a good practice to encroach on the code safety factor.

Thanks