I have seen similar problems, we had a 4" x .237 running about 60 psi on a produced water line it corroded a spot similar in size with no corrosion anywere else in the line. it was determined after that it was just a "soft spot" in the pipe.
Keep in mind, radiography has limititations. Just because you don't see a defect, doesn't mean one wasn't there.
There may have or may not have been a defect, but given your description of water cut with salts, it's possible the line may have had a shallow spot as Al suggested.
Also, given water etc, Don't throw out the possibility of localized MIC. In short the possible causes are numerous, and without more detailed information, no firmer answer can be given.
Hello Kix, very good point, I believe that phenomenon is referred to as eddy effect and can be especially common in steam applications. Best regards, Allan
can you elaborate on "just above flush root" the pipe job we are working on( mentioned in another thread) are fittings for a steam turbine and I'd like to know what to watch for!
Well, flush is when you basically have no root above the ID of the pipe. Example, you could run your finger over the root and you wouldn't feel anything. If it were sucked back you would feel a divot because it is undefiled. Just above flush, is when you have a 1/16th or a 3/32" of root reinforcement all the way around the inside of the pipe. The old wedding band, which I'm sure, you've heard. Depending on the code you are working to and the application of the line is what will dictate how much reinforcement you can have. If no one tells you different, then just go by the code if you have a heavy spot. My rule of thumb is never over 1/8" root reinforcement.
One of the issues that occurs with a flush bead is the bead and HP are put in with GTAW then fill and cap with LH Everything looks good until the fill and pass and then the bead starts rising. You have to control the temp of the following passes.
Years ago I have seen on salt water injection lines where the lands are jammed up and a bead is skated in. No grinding of the bead and a hot pass is run really fast. The fill and pass are done. You have IP all the way around. The lines run 2800psi. Running a standard bead the lines erode out in as few as 60 days. The 100% ip will last up to 6-8 months. This is not common and I have seen few companies do this lately as there are now fiber reinforced resin materials that can hold up to the pressure and corrosive environment.
BABRt's
Well, We have Done the following;
the whole pipe line and Hook up went out of service, and we radiographed about 40% of all weld joints and found that the corrosion exists in a severe conditions in about 50 % of all radigraphed, and the corrosion dont exist only in welds, but the adjacent parent metal were severly corroded too, about 50% percent too, also we radiographed a random set of welds - different welding procedures, different materials, different welders, and different welding electrodes patches - and the problem exists regardless of the mentioned factors,
we also radiographed other welds on different pipelines of the same Material and welding procedure but found, no corrosion, the problem is going to be that the line was not adequatically protected from corrosion
previous analysis of the Fluid show that a high percent of salts as I said and Carbonic Acid too, coupled with high operating temp, above 100 Celisus, and High water cut and flow rate and pressure, above 100 psi
we think this is more likely a problem with material selection or inadequate protection through using inhibitors
Thanks All
Topic Welding Industry / Inspection & Qualification / Weld Corrosion on Low Carbon Steel Pipe Line ?
