The attenuation 7 dB/m at 16 kHz for unburied bitumen coated pipe seems to be rather high.
Poor SNR results might have been caused by the discrete magnets layout used for the study.
The discrete layout should undermine the SNR due to multiple blind sports around the sensor.
17:20 Nov-22-2010 Florin Turcu R & D, Dept. of Electrical Systems and Automation - University of Pisa, Italy, Joined Jul 2007 9
Re: Effect of attenuation on inspection range and sensitivity in Long-Range Guided Wave NDT of coated and buried pipesIn Reply to Sergey Vinogradov on 05:25 Nov-22-2010 (Opening).
It is generally known that attenuation depends among others, on pipe state, thickness and health of bitumen coating, its attachment to the pipe and frequency.
Our test refers to a specific pipe, so it's difficult to generalize the results, extending them to all the bitumen coated pipes. Some issues that were specific to this case and that influenced attenuation rate would be:
- The pipe state: very old and heavily corroded, and with big metal loss artificial defects (approximately 20cmx20cm, 50% depth); Both heavy generalized corrosion and large metal loss defects have important influence over the attenuation rate.
- The collar of sensors used only for acquisition did not have permanent magnets installed, but used the residual field of the magnetostrictive strips.
To conclude, the attenuation could also be lower or higher than 7dB/m in other cases of pipes coated with bitumen and therefore have different inspection range.
21:10 Nov-22-2010 Sergey Vinogradov Engineering, , Southwest Research Institute, USA, Joined Nov 2010 2
Re: Effect of attenuation on inspection range and sensitivity in Long-Range Guided Wave NDT of coated and buried pipesIn Reply to Florin Turcu on 17:20 Nov-22-2010 .
if the pipe condition by itself is as bad as you described then it might attenuate guided waves dramatically even without coating.
I understand the intention of the paper was to shear the test result with the audience.
However, the MsS service providers would better 'normalize' their data to deliver a very well balanced message to readers.
Feasibility study on test mockups performed here in San Antonio proved the MsS/MsT transducers could reliably detect 10% anomaly at 27 ft in 10'' bitumen coated and buried pipe using 16 kHz T-mode. The SNR next to the transducer was about 66 dB though. As far as I understood, in your case, the SNR in the beginning was about 40 dB. This kind of SNR is not really the best compared to what can be accomplished with the current capability of MsS technology.