Abstract
The detection and sizing of fatigue cracks in ferritic materials, especially in offshore structures, is of major importance. This paper describes an eddy current system to detect such cracks, operating in an offshore environment with a search probe to electronic instrument separation of up to 600 m. An analysis of the various factors influencing the search coil behavior is given in terms of a mutually coupled primary and secondary electrical circuit; the component values of which are influenced by the coil design, induced electrical currents in the material, and any defects it contains. It is further shown that, with proper coil parameters, the phase variation in the phase angle of the coil complex impedance can be kept almost constant compared with the rapid variation occurring during lift-off. This behavior can be exploited in the instrumentation to give a clear vector display indication of the crack presence on less than ideal surfaces.
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References
C. V. Dodd, The use of computer-modelling for eddy-current testing,Research Tech. in N.D.T. Vol. 3, Chap. 13 (Academic Press, New York, 1977), pp. 429–479.
B. A. Auld, F. Muennemann, and D. K. Winslow, Eddy current probe response to open and closed surface flaws,J. Nondest. Eval. 2: 1–21 (1981).
S. Ramo, J. R. Whinnery, and T. Van Duzer,Fields and Waves in Communication Electronics (John Wiley & Sons, New York, 1965).
A. Gopinath and B. Easter, Moment method of calculating discontinuity inductance of microstrip right angled bends,IEEE Trans.Microwave Theory Tech. MTT-22: 880–883 (1974).
A. H. Kahn, R. Spal, and A. Feldman, Eddy current losses due to a surface crack in conducting material,J. Appl. Phys. 48: 4454–4459 (1977).
R. F. Harrington,Time Harmonic Electromagnetic Fields (McGraw-Hill, New York, 1961).
R. Langman, A new eddy current technique for crack detection and measurement,Brit. J.N.D.T. 21: 84–87 (1979).
W. Stumm, In-service nondestructive inspection of heavy loaded structures in particular underwater structures with leakage flux methods,Brit. J.N.D.T. 25: 124–126 (1983).
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McNab, A., Hale, J.C. Electromagnetic crack detection in ferritic steel. J Nondestruct Eval 4, 165–175 (1984). https://doi.org/10.1007/BF00566222
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DOI: https://doi.org/10.1007/BF00566222