enginerding
Structural
- Oct 3, 2006
- 205
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?
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?
