UT Thickness Results are inaccurate for an on-line pipe?
UT Thickness Results are inaccurate for an on-line pipe?
(OP)
I had some UT thickness results back claiming a pipe was significantly thicker than its nominal thickness! We believe that this is because the pipe was on-line at the time, so the temperature of metal altered the speed of sound within the material, making the UT device think that the pipe was thicker than it was. Is there any calculation I can do that will allow me to convert this hot UT reading into something more sensible?
Many Thanks
Many Thanks





RE: UT Thickness Results are inaccurate for an on-line pipe?
I'd bet simply that someone put the wrong pipe there.
RE: UT Thickness Results are inaccurate for an on-line pipe?
RE: UT Thickness Results are inaccurate for an on-line pipe?
Highly unusual.
Instrument damage?
What's it carrying. Is there any chance of fluid solidification against the wall?
RE: UT Thickness Results are inaccurate for an on-line pipe?
Are the readings taken at the exact same thickness measurement location? If at the same pup piece, but different orientations then the readings are within mill tolerance. One side could be a bit thin, while the other is a bit thick. This is more likely with seamless pipe, of course. The 5.8mm reading is an outlier, it is possible you have localized corrosion / pitting.
As BigInch says, not likely that the pipe temperature is causing this amount of change. What material, and what temperature?
RE: UT Thickness Results are inaccurate for an on-line pipe?
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: UT Thickness Results are inaccurate for an on-line pipe?
RE: UT Thickness Results are inaccurate for an on-line pipe?
Elevated temperature is NOT the source of your error. As temperature increases so does the velocity of sound which would decrease the apparent thickness of the pipe. A more likely cause is the instrument was calibrated on a material with a different velocity. If the results are "too thick" that would indicate the material used for calibration had a faster material velocity. For example, the velocity of sound in wrought iron is about 20% faster than in cast iron. IF you can determine what material was used to calibrate the instrument (and it is in fact different from the pipe material) you can calculate the error in thickness as the ratio of the two velocities.
JR97
RE: UT Thickness Results are inaccurate for an on-line pipe?
RE: UT Thickness Results are inaccurate for an on-line pipe?
RE: UT Thickness Results are inaccurate for an on-line pipe?
Thanks for getting back to us to close the loop. Always nice to know what the solution to the mystery is!