Detection of cracks in ferromagnetic steel structures by the eddy current method is often limited by additional noise associated with magnetic and structural heterogeneity, especially when it is necessary to detect structural cracks through a layer of dielectric anti-corrosion coating. A promissing approach to problem solution is based on the use of selective eddy current probes, which include the eddy current probes of double differential type. One of the features of such eddy current is the possibility of detecting hidden defects even through a layer of dielectric anti-corrosion coating. In this paper, the limiting possibilities of crack detection using an improved low-frequency eddy current probe of double-differential type with a diameter of 15 mm and a smartphone based eddy current flaw detector were investigated. This probe provides a high depth of penetration necessary to detect defects under the dielectric coating. The greater depth of penetration of this probe is achieved by increasing the diameter of the windings, the distance between them and the number of turns. The research was carried out using a rectangular specimen, in which a large crack (or through wall structure fracture) was simulated by a joint of two identical polished rectangular parts. The assembled specimen was covered with dielectric plates of different thicknesses up to 25 mm thick to simulate anti-corrosion coating of different thicknesses. It is shown, in particular, the possibility of detecting large cracks or structural fractures through an anti-corrosion dielectric coating up to 25 mm thick. The principle of design of an eddy current flaw detector based on a smartphone using the EddySmart application, which can provide remote control of ferromagnetic steel structures with wireless transmission of inspection results via mobile communication channels and the use of autonomous automated scanners, is considered.

1. Aerospace NDT: ASNT Industry Handbook. Bossi, R.H., Ed.; The American Society for Nondestructuve testing, 2014.

2. Zolfaghari, A.; Zolfaghari, A.; Kolahan, F. Reliability and sensitivity of magnetic particle nondestructive testing in detecting the surface cracks of welded components. Nondestructive Testing and Evaluation. 2018, 33(3), 290-300. https://doi.org/10.1080/10589759.2018.1428322

3. Goldberg, L. The use of Eddy Current for Ferritic Weld Testing in Nuclear Power plants. Materials Evaluation. 2003, 12, 1274-1278.

4. Nondestructive testing handbook, 3rd ed.; Vol. 5, Electromagnetic testing, Udpa, S.S., More, P.O., Eds.; American Society for NDT, 2004.

5. Uchanin, V.; Nardoni, G. Detection of cracks in ferrous steel structures: new innovative eddy current techniques. Procedia Structural Integrity. 2019, 16, 198-204. https://doi.org/10.1016/j.prostr.2019.07.041

6. Blitz, J.; Oaten, S.R.; Hajian, N.T. The testing of ferromagnetic metals with eddy-currents. Nondestructive Testing Communications. 1986, 2, 189-200. https://doi.org/10.1080/10589758608952927

7. Cecco, V. S.; Carter, J. R.; Sullivan, S. P. An Eddy Current Technque for Detection and Sizing Surface Cracks in Carbon Steel. Materials Evaluation. 1993, 51(5), 572-577.

8. ASTM International. Standard Practice for Eddy Current Examination of Steel Tubular Products Using Magnetic Saturation; ASTM E309-16; 2016.

9. Cecco, V. S. Design and specifications of a High Saturation Absolute Eddy Current Probe with internal reference. Materials Evaluation. 1979, 37(13), 51-58.

10. Cecco, V. S. Eddy current discontinuity probe utilizing a permanent magnet bobbin with at least one A.C. energized coil mounted in a groove thereon. US 3952315, 1976.

11. Uchanin, V. Surface eddy current probes of double differential type as an effective tool to solve non-destructive inspection problems. The Paton Welding Journal. 2023, 2, 46-55. https://doi.org/10.37434/tpwj2023.02.07

12. Fracture mechanics and strength of materials: Handbook. Strength and durability of airplane materials and structural elements, Vol. 9; Ostash, O., Fedirko, V., Eds.; Spolom, 2007. (in Ukrainian).

13. Uchanin, V.; Ivashenko, K. Detection of defects in ferromagnetic steel structures through an anticorrosion coating layer without removing. Methods and devices for quality control. 2021, 1(46), 5-14. (in Ukrainian). https://doi.org/10.31471/1993-9981-2021-1(46)-5-14

14. Petryk, V.; Protasov, A.; Galagan, R.; Muraviov, A.; Lysenko, I. Smartphone-Based Automated Non-Destructive Testing Devices. Devices and Methods of Measurements. 2020, 11(4), 272-278. https://doi.org/10.21122/2220-9506-2020-11-4-272-278

15. Petryk, V.F.; Protasov, A.G.; Syeryy, K.M.; Povshenko, O.A. Use of serial mobile devices when designing portable defectoscopes. Scientific notes of Taurida National V.I. Vernadsky University. Series: Technical Sciences. 2019, 69(6-2), 12-16. (in Ukrainian). https://doi.org/10.32838/2663-5941/2019.6-2/03

16. Lecoeur electronique US-WEB. https://www.lecoeur-electronique.net/us-web.html (accessed 2024-03-17).

17. Zhang, D.; Tian, J.; Li, H. Design and Validation of Android Smartphone Based Wireless Structural Vibration Monitoring System. Sensors. 2020, 20(17), 4799. https://doi.org/10.3390/s20174799

18. Xie, B.; Li, J.; Zhao, X. Research on Damage Detection of a 3D Steel Frame Model Using Smartphones. Sensors. 2019, 19(3), 745-762. https://doi.org/10.3390/s19030745

19. Yu, Y.; Han, R.; Zhao, X.; Mao, X.; Hu, W.; Jiao, D.; Li, M.; Ou, J. Initial validation of mobile-structural health monitoring method using smartphones. Intern. Journ. of Distributed Sensor Networks. 2015, 11(2), 1-14. https://doi.org/10.1155/2015/274391

20. Felice, M.; Heng, I.; Udell, C.; Tsalicoglou, I. Improving ultrasonic inspector productivity with modern mobile technology. Singapore International NDT Conference & Exhibition, 4-5 Dec 2019. e-Journal of Nondestructive Testing. 2019, Vol. 25(4). https://www.ndt.net/?id=25142 (accessed 2024-03-17).

21. Mook, G.; Simonin, Y. Smartphone turns into eddy current instrument. 12th European Conference on Non-Destructive Testing (ECNDT 2018), Gothenburg 2018, June 11-15. e-Journal of Nondestructive Testing. 2018, 23(8). https://www.ndt.net/?id=22704 (accessed 2024-03-17).

22. Mook, G.; Uchanin, V.; Lysenko, Ju. Research of eddy current probes for inspection of aluminum alloy welding using smartphone-based flaw detector. Technical diagnostic and Nondestructive Testing. 2024, 3, 32-38. (in Ukrainian). https://doi.org/10.37434/tdnk2024.03.05

23. Udell, C.; Maggioni, M.; Mook, G.; Meyendorf, N. Improving NDE 4.0 by Networking, Advanced Sensors, Smartphones, and Tablets. Handbook of Nondestructive Evaluation 4.0, Meyendorf, N., Ida, N., Singh, R., Vrana, J., Eds.; Springer, Cham. 2022. https://doi.org/10.1007/978-3-030-73206-6_53

24. https://auremo.org/materials/stal-os.html (accessed 2024-03-17).