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Vol.9 No.1 AASP16 (122) - AA123- 124 GA21 NT83-84

Academic Articles

Regular Paper

Vol.9 No.1 (2017) p.15 - p.25

Effect of Scaly Structure on the Measurement of Pipe Wall Thickness using EMAT

Hongjun SUN¹, Ryoichi URAYAMA², Tetsuya UCHIMOTO², Fumio KOJIMA², Toshiyuki TAKAGI^2,*, Hiroshi ABE³, Kunihiro KOBAYASHI⁴

¹ Graduate School of Engineering, Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi 980-8577, Japan
² Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba, Sendai, Miyagi 980-8577, Japan
³ Graduate School of Engineering, Tohoku University, 6-6-01-2 Aoba, Aramaki, Aoba, Sendai, Miyagi 980-8579, Japan
⁴ Tohoku Electric Power Co., Inc., 1-7-1 Honcho, Aoba, Sendai, Miyagi 980-8550, Japan

Abstract

To use an electromagnetic acoustic transducer (EMAT) to measure the thickness of a carbon steel pipe wall, the electromagnetic acoustic resonance (EMAR) and pulse-EMAR methods have been proposed previously. In this paper, the EMAR and pulse-EMAR methods are used to measure the wall thickness of the dorsum part of a bent carbon steel pipe that has experienced flow accelerated corrosion (FAC). The received signals are processed using superposition of nth compression (SNC). The measurement results obtained with the EMAR and pulse-EMAR methods are compared with equivalent measurements of minimum thickness using a caliper gauge, and the RMSE discrepancies are 0.24 mm and 0.36 mm, respectively. The results show that these discrepancies can be attributed to the scaly structures created by FAC. Further investigation shows that even larger discrepancies exist between the pulse-EMAR measurements and the minimum-thickness caliper measurements, again mainly in the parts affected by FAC. Typical parts of the pipe wall are observed using a three dimensional confocal laser scanning microscope, which reveals differently shaped scaly structures in different parts of the specimen. The pulse-EMAR signals are simulated numerically. These results show that the pulse-EMAR method measures thickness accurately in the initial stages of FAC, but that discrepancies gradually increase. The pulse-EMAR results include all the surface conditions in the measurement region under the probe. According to the numerical analysis, combining the pulse-EMAR and SNC methods might lead to the thickness of only the pristine part of the measurement area being registered, which might explain the discrepancies obtained in the measurements.

Keywords

Electromagnetic Acoustic Transducer, Electromagnetic Acoustic Resonance, Pulse-EMAR, Flow Accelerated Corrosion, scaly structure, Ultrasonic

Full Paper: PDF EJAM Vol.9 No.1 pp.15-25 "Effect of Scaly Structure on the Measurement of Pipe Wall Thickness using EMAT"

Article Information
Article history:
Received 13 January 2017
Accepted 11 May 2017


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