X-ray inspection

[lamari]

Hi,

we have experienced corrosion failures in a 6 inch SCH 80 flowline (3 mm CA) in a oil production facilities. We know that the corrosion is due to CO2 and water accumulation in the low points of the flowline. Unfortunatelly we have not received the chemicals yet to protect the flowlines and as per the flowline desing we cannot launch any pig (or intelligent pig).

The pipes are wrapped and buried (about 1.5 m) and I would like to perform a quick assesment of the integrity of that flowline. As said, since the flowline is wrapped, I cannot easly do a UT. So I'm thinking on doing a spot X-ray inspection. Now the line is full of water. What I would like to know is if the X-ray inspection procedure of a pipeline in service differs from a X-ray inspection procedure used for welding control.

I guess the exposition time and distance should not be the same for each inspection procedure, but I have no clue which could be a convenient range.

My concern is that all the UT we have done (in the above ground pipework) and the corrosion coupon inspection do not reveal such a high corrosion degree. However in two months we experienced three oil leaks at one of the lowest points of the flowline.

Thanks in advance.

 

[stanweld]

I had a similar corrosion problem on an above ground 4" oil flow line. Pitting was localized and the rate was high (approximately 100 mils per year). I used to X-Ray to determine extent of the area and followed with UT for pit depth measurement.

 

[brimmer]

If the line has liquid in it (water or oil) you will not be able to perform x-ray, it would need to be empty. X-ray would give more of a qualitative idea of corrosion in this case with shadow shots. I don't know why you couldn't remove the coating and complete UT, then recoat?

 

[lamari]

Thanks for your answer. Yes, we were proceeding with the UT but I wanted to organize several inspection teams working in paralel.