Crack on Oil Line

[gasoperations]

A underground crude oil line had a unusual failure recently as indicated in attached picture.

It was a crack type failure but UT inspection on crack location and on near by material did not find any internal / external corrosion or any material defect like inclusion, lamination etc.

Pipe line is about 40 years old with 5L-X52 spec. and 9.5 mm thk. Operating at about 100 psig / 150 degF

Could any body have any suggestion for possible failure mechanism

Thanks

 

[metengr]

gasoperations;
Is the OD surface of this line coated? It looks like a series of pin-hole leaks but I could not tell if what I am viewing is the actual exterior surface of the underground pipe or a coating.

How did you perform NDT to conclude the above? Did you send a crawler robot down the pipe to view the ID surface and conduct NDT? If not, I would recommend it.

 

[stanweld]

Advise cleaning the pipe and MT area. It's very difficult to ascertain anything from the photo, other than the leak. There appears to ba a leak at the top portion of the pipe inthe photo.

 

[brimmer]

To repeat what others have said, you need to clean the line in the area and do NDE, or post these photos if you already have done this to help us help you. It appears this may be corrosion and not cracking. If NDE has inspected this area before or now and is telling you there is nothing there, get new NDE people. Usually during a hydrotest if it is a crack, the pipe will rupture and form a larger opening. From the photo the pipe has not done this. To me just from the one photo it could be internal corrosion, leaking at pinholes.

 

[gasoperations]

Metengr-
OD surface is coated with a tape wrapping which has deteriorated over last 40 years.
UT inspection was carried out by an ASNT-II technician over the crack and nearby area, but nothing abnormal was detected
Crawler can not be sent inside the pipe as it a live and very long line, though future intelligent inspection is planned.

Stanweld- Some more closeups are encliosed for further review.

Brimmer - information as above


Additional information:
This the second time that this type of failure has occoured in less than one year.

The crude oil has some sulfur ( o.38%wt. ) and some H2S which appears to be increasing over last 10 years. 10 - 20 ppm H2S has been detected in the confined vapour space of the storage tanks. Please remember this is not the H2S measured from the crude oil sample but the free H2S in the vap. space. There may be some more H2S dissolev in the crude.

Could this be HIC??

 

[Metalguy]

Could easily be HIC given the increase in H2S. Not good news for the entire pipeline.

Check this abstract:

http://journals.cambridge.org/actio...80&jid=MAM&volumeId=11&issueId=S02&aid=327079

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[metengr]

Yes, I do agree based on additional information, see the paper below for review;

https://www.corrdefense.org/Technic...al Selection and Operation Control Issues.pdf

 

[gasoperations]

Thanks guys

Now, is there any way to check / confirm / evaluate if the line is under HIC attach. Any inspection or test on the line. The leak spot is already under welded box sleeve (After installing mechanical clamp). So the pipe surface is not accessible near the leak.

Is intelligent pig inspection for crack detection may be usefull for detecting cracks which may be developing at other location?

Thanks

 

[stanweld]

Tend to agree with metengr and metalguy. Does not bode well for the future of the pipeline. Have leaks been at low points in the line where water might collect? If so, you should concentrate your inspection efforts there.

 

[SJones]

Your supposed UT inspection around the 'crack' should have picked up HIC, it's pretty difficult to miss. With a second leak in a year, surely the pipeline integrity alarm bells must be ringing. You can try Googling the terms ICDA, ECDA, PDAM, ILI, but you would be better off employing expert help to assess the fitness for service of the pipeline.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[gasoperations]

Thanks every body for information. Will try to involve some external expert help.

 

[brimmer]

Smart pig (crack detection tool) should easily be able to detect these cracks and others like it. Don't know what the diameter of the pipeline is, but they come as low as 6 inch now.
If you do more digs, make sure to clean the surface and complete MPI (not just UT inspection), if you can see the morphology of the cracks it will help. If we had a picture of the indication with MPI we would be able to most likely give you a definite answer on what type of crack this is. I still don't want to take a guess, with HIC I have seen on pipelines the cracks are not usually this long (though there is no scale). Could be HIC, SSC, I wouldn't rule out regular external SCC (given that it is tape coating), or even a manufacturing defect (like lamination that has grown from fatigue over time).
Not to beat a dead horse, but really the NDE crew should have detected something, how can they not?

 

[blacksmith37]

How about an out of the "box" possibilty ? Stress corrosion cracking - not related to H/sulfur. This is an unusual problem nearly always limited to gas trans lines; but I have seen in in one oil line (not published except in 1979 NACE paper on Failure Analysis). Conditions are :1- Elevated temp, 2-Cathodic potential below protective (under disbonded wrap or in a shorted casin),3- cyclic stresses (I don't know if you have that ; my line came from a refinery and switched products daily). Evidence is few + (parallelish) cracks containing black iron carbonate (siderite as I remember).
MCI or Stress Engr in Houston should be good help; more than a few consultants could miss this one,if you have it.

 

[stanweld]

Confirming comments by blacksmith 37, at the 150 F operating temp, soil induced SCC is quite possible/probable. No cold applied tape coating would provide adequate protection at the elevated temperature based on testing that I performed and published over 30 years ago. I would assume that impressed current levels would have increased over time as well due to the coating deteriorization.

 

[gasoperations]

Further information is as below:
- Line size is 40"
- Actually MPI was considered but due to leaking oil from the live line, we had to abandon the idea.
- UT was carried out but there was nothing unusual found.
- Actually this line had other leaks also in the past but all leaks were due to external corrosion due to wrapping damage and associated corrosion. Only the last two failures in one year were like this strange crack like appearance.
- There are three grades of oil transported through the line in batches but line is always under operation with many batches of these grades of oil from a producing field to the tank farm. One of the batch is at elevated temp of 150 OF but other two are at normal ambient temperature

Thanks

 

[Guest102023]

Surely the pipeline is now out of service and the leaking section condemned. Cut out the offending section and have a qualified failure analysis lab look at it. They should have considerable experience with crude corrosion and pipelines. Cleaning up the surfaces should yield answers to an experienced set of eyes.

Given the multiple leaks it appears that low frequency ERW issues are not a determining factor. But whatever amount of this pipe remains in service, this is an issue that requires your proper diligence in future.


FWIW, I googled a picture of that Enbridge leak last year in western MI in a local online newspaper - it was a single, long, very straight longitudinal split; my best guess is corrosion along an ERW seam.