The Parameters Optimization Of Eddy Current Testing For Tubes Based On Finite Element Analysis

The eddy-current examination is one of the big five conventional non-destructive testing technologies. Its advantages are easiness of coupling, high speed, low cost and easiness of automation. Therefore it has played more and more important role in nuclear power, aviation, the petrochemical, electric power, metallurgical and other industries. Every year a large amount of metal tubes are used in above industries. NDT of the tubes is immediately related to economic benefit and safety of persons. Many countries pay more and more attentions to the NDT of metal tubes. However the eddy-current examination has limitations, for example it is influenced by many factors which give rise to false indications. The false indications restrict the application of eddy current inspection to a certain extent because of difficulty in discrimination between false and real indications. For a given probe and an eddy curret instrument combination, the parameters under which the instrument is operated for inspection are very important for the efficiency of the inspection. Among the parameters exciting frequency is the most important one governing the sensitivity and reliability of the inspection. To carry on the examination more efficiently, the parameters, especialy the exciting frequency, must be set appropriately. This article discusses the methods widely used to find the best parameters including frequency for eddy-current examinations. It is pointed out that the methods are not accurate enough for finding the optimum frequency, the frequency found most probably by the methods is a little far from the optimum. In this case, the best efficiency of the inspection is not reached. Therefore this article develops a new method for finding optimum exciting frequency of eddy current testing by numerical modeling based on modern eddy current testing theory and technology. The development of the new method is aimed at overcoming the shortcomings of existing methods, i.e. finding the optimum frequency rather than the good ones.This article analyzes eddy current testing of stainless steel tubes with inserted and encircling probes. ANSYS software is used to simulate the flaw signals of the eddy current testing of the stainless steel specimen tubes with OD and ID artificial flaws using different exciting frequencies. The calculated flaw signals, the "8" figures, are plot. With the same frequencies as used in simulation, experimental eddy current testing of the specimen tubes is conducted and the flaw signals from the artificial defects are recorded. The agreement between the simulated "8" figures and those obtained by experimental testing is very well.Based on above mentioned investigations, the new method can be established as follows: Simulation of flaw signals of eddy current testing with different frequencies using ANSYS software. Comparison of the signal patterns obtained with different exciting frequencies. Choice of the frequency with which both the signals from OD and ID artificial defects are higher and the phase difference between the signals from OD and ID artificial defects reaches nearly the maximum. The advantages of the eddy current testing of tubes with the frequency chosen by using the new method are higher sensitivity and possibility of differentiating between OD and ID flaws by the phase of its signal.