INFLUENCE OF SPEED EFFECT IN EDDY CURRENT NONDESTRUCTIVE TESTING

Abstract Eddy current testing has been used for high speed nondestructive testing of materials with simple shapes such as bars, tubes, and wires. It is known that the high relative speed between the test coil and tested material has some influence on the test indications. There have been many reports on the speed effect in eddy current testing till now. Those reports have mainly clarified the quantitative speed effects for a certain test condition and the fundamental characteristics of the speed effect has remained obscure. The authors have investigated the effect by combining Doppler effect and the phase velocity of electromagnetic field to qualitatively elucidate the speed effect in eddy current testing. The investigation leads to the following facts. The speed effect is determined by the ratio of the test speed to the phase velocity of electromagnetic field diffusion in the tested material. The higher the frequency of eddy current testing is, the smaller the speed effect is.