Akira Nishimizu

SIGNAL EVALUATION SYSTEM OF FLEXIBLE ARRAY ECT PROBES FOR INSPECTING COMPLEXLY SHAPED SURFACES

We developed a signal evaluation system of flexible array eddy current testing (ECT) probes for inspecting complexly shaped metal surfaces. Our probes employ excitation and pickup coil pairs arrayed on a bendable substrate to measure curved targets. Since the developed probes produce signals due to the change in the relative position between the coil pair, an evaluation module for flaw signal identification is integrated into the system. The identification utilizes signal phase combination of the coil pairs. It is represented as a two‐dimensional diagram constituting the phase values of two of the coil pairs with different positions. The phase of signals around flaws is significantly affected by their orientations. The diagram is therefore capable of separating flaw information from other information and of imaging flaw positions. We applied the system to complex geometric mock‐ups. Flaw signals were successfully identified and the images obtained for identified positions could be used to efficiently meas...

Eddy Current Testing and Sizing of Deep Cracks in a Thick Structure

Due to the skin effect of eddy current testing, target of ECT restricts to thin structure such as steam generator tubes with 1.27mm thickness. Detecting and sizing of a deep crack in a thick structure remains a problem. In this paper, an ECT probe is presented to solve this problem with the help of numerical analysis. The parameters such as frequency, coil size etc. are discussed. The inverse problem of crack sizing is solved by applying a fast simulator of ECT based on an edge based finite element method and steepest descent method, and reconstructed results of 5, 10 and 15mm depth cracks from experimental signals are shown.

Natural Crack Sizing Based on Eddy Current Image and Electromagnetic Field Analyses

An eddy current testing (ECT) system with multi‐coil type probes is applied to size up cracks fabricated on austenite stainless plates. We have developed muti‐channel ECT system to produce data as digital images. The probes consist of transmit‐receive type sensors as elements to classify crack directions, working as two scan direction modes simultaneously. Template matching applied to the ECT images determines regions of interest in sizing up cracks. Finite element based inversion sizes up the crack depth from the measured ECT signal. The present paper demonstrates this approach for fatigue crack and stress corrosion cracking.