DETECTION OF DEFECTS OF STRUCTURES FROM FERROMAGNETIC STEEL THROUGH THE LAYER OF ANTICORROSION COVER WITHOUT REMOVAL
Keywords:eddy current method, flaw detector, double differential probe, crack, sensitivity, noise, inspection productivity
The detection of the cracks in ferromagnetic steel components by the eddy current method is formidable because of the additional noise originated from magnetic and structural heterogeneities of the inspected material. In this paper, several techniques proposed for the detection of the defects in ferromagnetic steel components are analyzed. One of the possible approaches is based on the additional magnetization of the inspected zone to minimize magnetic heterogeneity. Another trend is concerned with new selective EC probe development. This inspection problem is exercisable by the double differential EC probes application. These probes were developed some decades ago and are characterized by a specific quasi-absolute signal with maximum amplitude when the probe is situated directly over a crack. The main features of such probes can be characterized with: high sensitivity to elongated (like crack) and to local (like pitting or pore) defects; high sensitivity to surface and subsurface defects through the protective coating or with large clearance between the probe and inspected surface; high penetration for low-frequency probes; high lift-off noise suppression. In this study the possibility to detect the cracks through the anticorrosive coating was investigated. Special detectability diagrams were created to estimate the ultimate thicknesses of dielectric coating for the detection of the defects with different depths. For inspection of the objects with large overall dimensions (like tubes, forgings, etc.) array type EC probe (named EDDYLINE) was developed. High sensitivity width (near 60 mm) was achieved to obtain high inspection productivity. At the same time, the high locality was provided because all EC probes are operated separately. Developed EC inspection techniques based on the EDDYLINE type EC probe were successfully applied for the detection of cracks in ferromagnetic and stainless steel tube forgings.
Fracture mechanics and strength of materials. Vol. 9: Strength and durability of airplane materials and structural elements / О.P. Оstash, V.М. Fedirko, V.М. Uchanin et al. – Lviv: Spolom, 2007. – 1068 p. (in Ukrainian).
Zolfaghari A., Zolfaghari A. and Kolahan F. Reliability and sensitivity of magnetic particle nondestructive testing in detecting the surface cracks of welded components // Nondestructive Testing and Evaluation. – 2018. – Vol. 33. – №3. – P. 290-300.
Goldberg L. The use of Eddy Current for Ferritic Weld Testing in Nuclear Power plants // Materials Evaluation. – 2003. – № 12. – P. 274-1278.
Udpa, S.S., More P.O., eds. (2004). Nondestructive testing handbook (third edition), Vol. 5, Electromagnetic testing. American Society for NDT.
Uchanin, V.M. Eddy-current flaw detection in structural elements // Materials Science. – 2006. – 42. – 494-501. doi.org/10.1007/s11003-006-0106-5.
Lutcenko G., Uchanin V., Mischenko V., Opanasenko A. Eddy Currents Versus Magnetic Particles. Proc. 18th World Conf. on Nondestructive Testing, 2012. Durban. http://www.ndt.net.
Blitz, J., Oaten S.R. and Hajian, N.T. The testing of ferromagnetic metals with eddy-currents // Nondestructive Testing Communications. – 1986. – № 2. – P. 189-200.
Patent U.S. № 3952315. Eddy current discontinuity probe utilizing a permanent magnet bobbin with at least one A.C. energized coil mounted in a groove thereon // Cecco V.S., 1976.
Cecco V. S. Design and specifications of a High Saturation Absolute Eddy Current Probe with internal reference // Materials Evaluation. – 1979. – Vol. 37. – № 13. – P. 51-58.
ASTM E309-16. Standard Practice for Eddy Current Examination of Steel Tubular Products Using Magnetic Saturation. – 2016. – ASTM International.
Patent № 60751, Ukraine. Eddy current probe for inspection of ferromagnetic steel structures // V. Uchanin, 2011 (in Ukrainian).
Uchanin V.M. Surface eddy current probes of double-differential type. Lviv:Spolom, 2013. – 268 p. (in Ukrainian).
Uchanin, V., Mook, G., Stepinski, T. (2002). “The investigation of deep penetrating high resolution EC probes for subsurface flaw detection and sizing.” Proc. 8th European Conf. for Nondestructive Testing. Barcelona. http:// www. ndt.net.
Mook G., Hesse J., Uchanin V. Deep Penetrating Eddy Currents and Probes // Materials Testing. – 2007. – Vol. 49, № 5. – Р. 258-264. doi.org/10.3139/120.100810.
Uchanin V., Lutsenko G., Dzhaganian А., Opanasenko A. The application of eddy current section in automated system for combined railway rolling stock axles inspection. 10 European Conf. on Nondestructive Testing. June 7-10 2010, Moscow. http://www.ndt.net.
Uchanin V., Lutsenko G., Dzhaganian А, Nikonenko A. Eddy Current Inspection of Steel Castings with Roughly Finished Surfaces. 10 European Conf. on Nondestructive Testing. June 7-10 2010, Moscow. http://www.ndt.net.
Bureau J.-F., Ward R.C., Julien A. Application of eddy current array technology to surface inspection. 18th World Conference on Nondestructive Testing. 2012. Durban, South Africa. http://www.ndt.net.
International Standard ISO 20339:2017 (E). Non-destructive testing. Equipment for eddy current examination: Array probes characteristics and verification. – Geneva: ISO/TC 135/SC 4, 2017.
Uchanin V., Nardoni G. Detection of cracks in ferrous steel structures: new innovative eddy current techniques // Procedia Structural Integrity. – 2019. – 16. – P. 198-204. doi.org/10.1016/j.prostr.2019.07.041.