Field Application of Electromagnetic Acoustic Resonance to Inspection of Pipe
Wall Thinning in a Nuclear Power Plant
Toshiyuki TAKAGIa , Ryoichi URAYAMA a, Toshiaki ICHIHARA a, Tetsuya UCHIMOTO a,
Taku OHIRA b and Takayoshi KIKUCHI b
a
b
Institute of Fluid Science, Tohoku University, Japan
Plant Management Department, The Japan Atomic Power Company, Japan
In piping systems of nuclear power plants, pipe wall thinning is caused by aging-related
flow-accelerated corrosion (FAC) and liquid droplet impingement (LDI) erosion. Piping maintenance is
based on residual lifetimes estimated by periodic measurements of thickness. High accuracy and
reliability of these measurements are mandatory in the nuclear power industry. Currently, ultrasonic (UT)
thickness gauges are used to inspect pipe wall thinning. Although UT thickness gauges provide
measurements with high accuracy of about 0.1 mm, these are sensitive to surface rusts and paints, and
require highly skilled workers to operate.
Electromagnetic acoustic transducers (EMATs), devices widely used in performing ultrasonic
measurements, provide non-contact measurements as ultrasonic waves are transmitted and received
electromagnetically. The technique offers advantages in methods requiring inspection and monitoring [3,
4]. The drawback of the EMAT is its low electromechanical conversion efficiency, which leads to low
sensitivity and low S/N ratio. One way to overcome this drawback is to introduce an electromagnetic
acoustic resonance (EMAR) technique [1]. Electromagnetic acoustic resonance (EMAR) has good
capability in determining either thickness or ultrasonic velocity, and also when applied to the analysis of,
for example. elastic constants or damping properties. The authors have proposed a signal processing
method, called the superposition of nth compression (SNC) method, to extract thickness of pipes from
EMAR spectral response data. The pipe thickness cut from a mock-up corrosion-test loop was accurately
determined using this signal processing method [2]. In addition, this method was applied to online
monitoring of pipe wall thinning in large-scale corrosion test loop. The results obtained in a real plant
environment showed that EMAR provided measurements with accuracies of about 10 m with high
reproducibility [3].
In this study, EMAR combined with the SNC signal processing method is applied to determine pipe
thicknesses within the piping system of a nuclear power plant. Sections of piping evaluated using EMAR
included those having long-term service, where thinning can produce scale-like surfaces and complicated
geometry. By comparing results obtained with EMAR and conventional UT thickness gauges, accuracy
and applicability of the determination are assessed. In addition, we propose the parameters to indicate the
reliability of evaluation.
References:
[1] M. Hirao and H. Ogi, EMAT for Science and Industry, Kluwer Academic Publishers, (2003), pp.83-102.
[2] R. Urayama, T. Uchimoto, T. Takagi, S. Kanemoto, Quantitative Evaluation of Pipe Wall Thinning by Electromagnetic
Acoustic Resonance, E-Journal of Advanced Maintenance, 2, (2010), pp.25-33.
[3] R. Urayama, T. Uchimoto, T. Takagi, S. Kanemoto, Online Monitoring of Pipe Wall Thinning with EMAR, HOZENGAKU
(Maintenology),
(in Japanese, accepted for publication).
Speaker Biographical Information
Toshiyuki Takagi (PhD, Professor) is Deputy Director of the Institute of Fluid Science, Tohoku
University. His research field includes electromagnetic nondestructive evaluation, plant lifecycle
management, and development of intelligent materials. He published more than 250 international and
domestic journal papers. He is also Editor-in-chief of International Journal of Applied Electromagnetics
and Mechanics.