Defects in Pipe
Defects in Pipe
(OP)
I posted this earlier in the "Structural Other Topics Forum", but I think maybe this is a better location for this discussion...
I was using a t-mic wall thickness gauge to verify the wall thickness of column pipes that were delivered in the field. The pipe was either API 5L-X42 or ASTM A252 Gr. C pipe, 66"Øx0.875". This section of pipe is 40'-0" long and is made up of five 8'-0" long cans. The pipe was rolled and welded, not spiral welded pipe. I checked the thickness of each can as I went down and all of them were coming out at roughly 0.880" thick. The last can measured 0.413". I moved the mic over about 2" and it read 0.88". I started checking a bigger area around this initial bad reading and found a somewhat random spattering of good and no good readings. The measured thickness is 7/8"; there is no pitting.
The gauge was consistently reading bad where the bad readings were found and consistently reading good where the good readings were found. There were a couple of spots where the t-mic provided a good reading with the mic axis running one direction and a bad reading with the mic axis perpendicular to the first spot. Maybe the edge of an internal imperfection?
All the bad readings ranged from .390" to .430" – right about half the thickness. We cut out a portion of the pipe so we could see if we could find some cracks or delamination, but it was impossible to see anything on the torch-cut edges. Oddly enough, even though the steel in the coupon tested no good in the pipe, after it was cut out, it tested fine everywhere.
I don't know what to think about this. The bad spots seem to be so small that they probably won't cause a problem, but so many of the locations tested badly. Because the bad readings are all roughly the same, I think the delamination, cracks, or other imperfections don't run through the thickness, but rather parallel the surface of the steel. Does this seem reasonable?
Have you had a problem similar to this before? Is this a common problem? Do you have any suggestions of testing we should perform, or questions I should ask the pipe supplier?
I was using a t-mic wall thickness gauge to verify the wall thickness of column pipes that were delivered in the field. The pipe was either API 5L-X42 or ASTM A252 Gr. C pipe, 66"Øx0.875". This section of pipe is 40'-0" long and is made up of five 8'-0" long cans. The pipe was rolled and welded, not spiral welded pipe. I checked the thickness of each can as I went down and all of them were coming out at roughly 0.880" thick. The last can measured 0.413". I moved the mic over about 2" and it read 0.88". I started checking a bigger area around this initial bad reading and found a somewhat random spattering of good and no good readings. The measured thickness is 7/8"; there is no pitting.
The gauge was consistently reading bad where the bad readings were found and consistently reading good where the good readings were found. There were a couple of spots where the t-mic provided a good reading with the mic axis running one direction and a bad reading with the mic axis perpendicular to the first spot. Maybe the edge of an internal imperfection?
All the bad readings ranged from .390" to .430" – right about half the thickness. We cut out a portion of the pipe so we could see if we could find some cracks or delamination, but it was impossible to see anything on the torch-cut edges. Oddly enough, even though the steel in the coupon tested no good in the pipe, after it was cut out, it tested fine everywhere.
I don't know what to think about this. The bad spots seem to be so small that they probably won't cause a problem, but so many of the locations tested badly. Because the bad readings are all roughly the same, I think the delamination, cracks, or other imperfections don't run through the thickness, but rather parallel the surface of the steel. Does this seem reasonable?
Have you had a problem similar to this before? Is this a common problem? Do you have any suggestions of testing we should perform, or questions I should ask the pipe supplier?





RE: Defects in Pipe
RE: Defects in Pipe
Steven C
Senior Member
ThirdPartyInspections.com
RE: Defects in Pipe
RE: Defects in Pipe
RE: Defects in Pipe
Your T-mic is actually a longitudinal straight beam transducer and instrument except instead of a display of the returned pulse as in a UT scope, there is a trigger level and timer which returns a decimal number directly proportional to the time from the initial pulse to the return signal, hence proportional to the thickness. When you calibrate the instrument you are setting the 'time' number to read as thickness. When you have a lamination in the plate the ultrasonic signal reflects of the lamination and returns to the instrument in about half the time as a signal which makes it to the ID resulting in a thickness reading of about 1/2 the pipe thickness.
RE: Defects in Pipe
Digital thickness meters should be used as "indicative" information, not for examining flaws.
good luck!