Hiroshi Hoshikawa

REMOTE FIELD EDDY CURRENT TESTING OF FERROMAGNETIC DOUBLE WALL TUBE

Abstract Ferromagnetic double wall tube has been under development to ensure the high reliability of the steam generator in fast breeder reactor. The airgap between the tube two walls should prevent the conventional nondestructive test methods from detecting defects especially in the outer tube wall. Thus the development of the in-service inspection technique of the double wall tube has become a necessity in the field. The authors have investigated the feasibility of applying the remote field eddy current technique (RFECT)to the in-service inspection of the ferromagnetic double wall tube. The energy flow and the distribution of low frequency electromagnetic field in the RFECf have been derived through finite element analysis. It has been shown that defects in both inner and outer tube walls can be detected with almost the same defect indication by RFECT if the air gap between the ube walls is as small as 0.04 mm.

Electromagnetic testing method using tangential coil for measurement of covering thickness and diameter of rebars in concrete

Reinforcing bar in concrete provide tensile strength of structure. So, a measurement of covering thickness and diameter of rebar is important in maintenance inspection of concrete structure. The electromagnetic testing are expected as the method that can estimate covering thickness and diameter of rebar simultaneously. Magnetic flux generated by an excitation coil must reach a rebar sufficiently, to estimate covering and diameter of rebar. However, conventional test coil systems, which had been previously designed in these works, were insufficient for that requirement. Therefore, a new mutual induction type test coil system was developed for measuring rebars. The system has two tangential excitation windings and they are connected differentially to generate concentrated magnetic flux around rebar. And two pickup coils, that are arranged co-axially and normal to rebar, are also connected differentially to eliminate unbalanced voltage for no existence of rebar. In addition, neural nets were employed to esti...

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.