Rapid flaw reconstruction for SG-ECT signals by an optimization technique
Y. Matsumoto, S. Kojima, H. Komatsu, F. Nakayasu, Nuclear Fuel Industries Ltd. , Osaka, Japan; H. Kishino, JAPEIC, Chiba, Japan
ABSTRACT
Eddy current testing (ECT) techniques have been widely utilised for the in-service inspection of steam generator (SG) tubing in Pressurized Water Reactor (PWR) nuclear power plants at every outage. According to technological advances of NDE, accurate and rapid flaw shape evaluation techniques are required for ECT techniques. We have proposed an eddy current flaw reconstruction system for general 3D model by using the pattern recognition technique and optimisation technique. As the first step in this system, an initial flaw shape is approximately estimated by a pattern recognition technique based on neural network. In the next step, the flaw shape is accurately estimated by optimisation using general 3D finite element simulator. In this step, the error between the measured and calculated signals is minimised by changing the estimated flaw shape in calculation model. In order to decrease the time consuming forward solution during the iteration, a "good" initial shape generated by the neural network -good means close to the global minimum- and the pre-calculated reaction data sets are utilised. The concept of reaction data sets is that anomalous region is defined by dividing SG tubing region into rectangular cells and the equations system for the anomalous region is calculated before iteration step. During iteration, the appropriate cells are selected to describe the flaw shape as a sub-region in the anomalous region and ECT signal can be calculated by solving this relatively small equation system. In this paper, we show examples and investigation results in order to illustrate the efficiency of the reconstruction system. Various kinds of 3D flaws are utilised for this demonstration.
Publication Source: First International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components , 20 - 22 October 1998, Amsterdam, Netherlands. Held by the Joint Research Centre of the European Commission. Publisher:Woodhead Publishing Limited
NDTnet
