BQ-02 Method for Estimating Crack Length and Depth using RBF in Eddy Current Testing
Creators: Daigo Kosaka
Haruyuki Hanawa and KoujiHirano
Publisher: name: IEEE
Year: 2025

The welded-steel tanks require periodic maintenance to prevent weld cracks caused by the weight of amounts of oil. The Magnetic flux leakage inspection or the magnetic particle inspection[1] is commonly used for the crack detection. The repair decisions are based on estimates of crack length obtained from the inspections resulting from the magnetic particle inspection. However, this method requires removing coatings from oil tanks to protect them from corrosion. This results in a significant amount of waste generated from sound coatings due to the need for repeated removal and reapplication of coatings for each inspection. The Eddy Current Testing (ECT) is widely known as an inspection can detect cracks over the coating. While ECT has the advantage of easily recording measurement results and quickly detecting minute cracks, it has limitations in accurately estimating the shape of cracks[2]. This is because the effects of crack length and depth, respectively cannot be separated from the amplitude of the ECT detection signals. We propose a new method for estimating crack length and depth using the response width as defined in ISO 15548-2:2019 and the maximum amplitude value of the ECT detection signal[3]. Response width is the length between -6 dB of the maximum amplitude when the length in the scanning direction is on the horizontal axis and the amplitude of the detection signal is on the vertical axis. The effectiveness of the proposed method was verified using the finite element method. The simulation model used is shown in Fig. 1. Fig. 2 shows the simulation results of plotting the "maximum value of the crack signal" and the "response width" of the reference cracks (depths of 0.5, 1, 1.5, and 2 mm and lengths of 3, 4, and 5 mm) and the estimated crack (depth of 1.7 mm and length of 4.5 mm) on an amplitude-response width plane. The result of estimating a crack of 4.5 mm in length by radial prescriptive function interpolation using nine reference cracks was 4.4 mm. In the presentation, we will show the measured results of applying the proposed method to defects with known geometry created by machining.References: [1] Bouteille, Patrick, M. Finckbohner and S. Lugin, QIRT congress proceeding (2012) [2] Noritaka Yusa, Haoyu Huang and Kenzo Miya, NDT & E International, Vol. 40, No. 3, pp. 185-191 (2007) [3] Hazardous Materials Safety Techniques Association, https://khk-syoubou.or.jp/pdf/guide/research/20_2024-03-et.pdf, in Japanese (2024)
The welded-steel tanks require periodic maintenance to prevent weld cracks caused by the weight of amounts of oil. The Magnetic flux leakage inspection or the magnetic particle inspection[1] is commonly used for the crack detection. The repair decisions are based on estimates of crack length obtained from the inspections resulting from the magnetic particle inspection. However, this method requires removing coatings from oil tanks to protect them from corrosion. This results in a significant amount of waste generated from sound coatings due to the need for repeated removal and reapplication of coatings for each inspection. The Eddy Current Testing (ECT) is widely known as an inspection can detect cracks over the coating. While ECT has the advantage of easily recording measurement results and quickly detecting minute cracks, it has limitations in accurately estimating the shape of cracks[2]. This is because the effects of crack length and depth, respectively cannot be separated from the amplitude of the ECT detection signals. We propose a new method for estimating crack length and depth using the response width as defined in ISO 15548-2:2019 and the maximum amplitude value of the ECT detection signal[3]. Response width is the length between -6 dB of the maximum amplitude when the length in the scanning direction is on the horizontal axis and the amplitude of the detection signal is on the vertical axis. The effectiveness of the proposed method was verified using the finite element method. The simulation model used is shown in Fig. 1. Fig. 2 shows the simulation results of plotting the "maximum value of the crack signal" and the "response width" of the reference cracks (depths of 0.5, 1, 1.5, and 2 mm and lengths of 3, 4, and 5 mm) and the estimated crack (depth of 1.7 mm and length of 4.5 mm) on an amplitude-response width plane. The result of estimating a crack of 4.5 mm in length by radial prescriptive function interpolation using nine reference cracks was 4.4 mm. In the presentation, we will show the measured results of applying the proposed method to defects with known geometry created by machining.References: [1] Bouteille, Patrick, M. Finckbohner and S. Lugin, QIRT congress proceeding (2012) [2] Noritaka Yusa, Haoyu Huang and Kenzo Miya, NDT & E International, Vol. 40, No. 3, pp. 185-191 (2007) [3] Hazardous Materials Safety Techniques Association, https://khk-syoubou.or.jp/pdf/guide/research/20_2024-03-et.pdf, in Japanese (2024)