Testing Of Steam Generator Tubes Research Articles

Simulation of eddy current testing of steam generator tubes with wear and secondary side magnetite deposits

The steam generator (SG) tubes of pressurised water reactors are prone to degradation and are periodically inspected using eddy current testing (ECT) techniques. SGs provide a safety barrier between the radioactive primary side and the non-radioactive secondary side. Historically, a major degradation issue was stress corrosion cracking of tubes made of alloy 600. In modern SGs, better resistance to stress corrosion cracking is observed with the replacement of alloy 600 by alloy 690. However, this alloy does not prevent tubes from wear at support locations or wear resulting from fretting with loose parts. Long-term operation of SGs also leads to non-volatile species accumulation in the secondary side of the SGs, mainly magnetite. Magnetite deposits may build up as a dense and solid material on top of the tubesheet (hard sludge) and also in the flow slots of tube support plates, therefore modifying the general flow pattern and velocity of the secondary fluid. This has detrimental effects on the safe operation of SGs. The clogging-up ratio of the flow slots therefore needs to be assessed. The development of an ECT simulation model to address tube wear and magnetite deposits in SGs is presented. This model is based on the CIVA NDT platform. A bobbin coil signal is simulated and its performance for tube wear and magnetite deposit evaluation is discussed.

Signal processing schemes for Eddy Current Testing of steam generator tubes of nuclear power plants

► Approximate the drafting component with a piecewise polynomial function and to eliminate the drafting noise through subtraction. ► Signal indication extraction strategy based on the wavelet decomposition. ► Classify the extracted signals based on factors of signal similarity and signal distance in addition with information of the sensor position and original design data. ► Identify the defect indication by means of both a neural network approach and a statistic method. In this paper, signal processing schemes developed for upgrading the Eddy Current Testing system utilized for In-Service Inspection of Steam Generator (SG) tubes of a Fast Breeder Reactor nuclear power plant are presented. Schemes for the wobbling noise recognition, signal indication extraction, defect signal classification, and the separation of mixed signals are proposed, and are applied to both signals measured in a SG mock-up and signals measured with short tube test-pieces in a laboratory environment. The signal indications are extracted based on a wavelet decomposition and threshold value approach in addition with the signal similarity and signal distance information in case of support plate signals. As it is possible for the position of a signal point to be adjusted based on the signature of the support plates, signals of a welding joint or a bending zone can be recognized based on the design or/and manufactory information. The mixed signals of defects and support plate are processed with the similarity analysis strategy and the identification of defect signals is performed by means of both a neural network approach and a statistic method. Satisfactory extraction and classification results are obtained for all the measured signals, which validated the efficiency of the proposed schemes.

A novel feature extraction for eddy current testing of steam generator tubes

For defect characterization in steam generator tubes, feature extraction to interpret eddy current testing (ECT) signals has been recognized as an important step. In this paper, we propose a new feature extraction from ECT signals for defect classification and defect sizing. Using the extracted features as an input vector, a multi-layer perceptron (MLP) neural networks are used to classify defect types and to predict defect size. Although the proposed method requires relatively fewer features for the defect classification, it provides not only a high level of classification accuracy but also promising robustness to noise. Moreover, for the prediction of defect size, the proposed method yields a comparable prediction accuracy even though it needs fewer features than the previous result.

Inverse analyses for natural and multicracks using signals from a differential transmit-receive ECT probe

This paper describes the inverse analysis in the frame works of a round-robin test for the testing of steam generator tubes by eddy-current testing (ECT). An ECT probe with high space resolution was newly proposed, for the purpose of better and easier crack shape evaluations. This new probe is applied to the round-robin test pieces including natural crack samples and a multicrack sample. Inverse problems of the crack shape reconstructions are solved by a fast forward simulator and the conjugated gradient method. Experimental ECT signals as well as results of reconstructions are shown. Treatments of a natural crack and multicracks are discussed.

Development of an Arrayed Multi-Coil Eddy Current Testing Probe with the Help of Numerical Simulation.

This paper describes a newly developed arrayed multi-coil probe for the testing of steam generator tubes by eddy current testing. Owing to the multi-coil arrangement, it is possible to detect cracks in the whole round of the tube without rotation. Geometry of the probe was decided with the help of numerical simulation, which leads to high detectability of the probe. The signals of this probe were predicted by the edge based finite element method, and comparison between experimental and numerical results showed good agreement. Furthermore, this probe is expected to be convenient to reconstruct the crack shape from its C-scan image.

A novel signal processing technique for eddy-current testing of steam generator tubes

In eddy-current testing of steam generator tubes of nuclear power plants, the signals of defects may be corrupted by noise and other nondefect signals arising from the probe lift-off and the structures attached to the tubes, resulting in unreliable detection and inaccurate characterization of defects. In this paper, a novel signal processing technique is presented to reduce the noise and nondefect signals by the use of a wavelet transform. The noise and nondefect signals are reduced by first decomposing testing signals into wavelet components and then modifying the wavelet coefficients. The defect signals embedded in noise and nondefect signals are reconstructed through the inverse wavelet transform of the modified wavelet coefficients. The results of processing the one-dimensional and two-dimensional signals from eddy-current testing of tube test pieces show that this signal processing technique is effective for extracting defect signals embedded in noise and nondefect signals.

Expert system to increase the reliability of the multifrequency eddy current testing of steam generator tubes (In French: English abstract) : Benoist, Ph.; Chadian, P. 6th European Conference on Non Destructive Testing, Nice (France), 24- 28 Oct. 1994. Vol. 2, pp. 1095–1099. ECNDT (1994)

Expert system to increase the reliability of the multifrequency eddy current testing of steam generator tubes (In French: English abstract) : Benoist, Ph.; Chadian, P. 6th European Conference on Non Destructive Testing, Nice (France), 24- 28 Oct. 1994. Vol. 2, pp. 1095–1099. ECNDT (1994)

Multifrequency eddy current testing of steam generator tubes using optimal affine transformation Review of progress in quantitative nondestructive evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. Vol. 7A, pp. 821–830. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988.

Multifrequency eddy current testing of steam generator tubes using optimal affine transformation Review of progress in quantitative nondestructive evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. Vol. 7A, pp. 821–830. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988.

Multifrequency eddy current testing of steam generator tubes using optimal affine transformation : Review of progress in quantitative nondestructive evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. Vol. 7A, pp. 821–830. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988.

Multifrequency eddy current testing of steam generator tubes using optimal affine transformation : Review of progress in quantitative nondestructive evaluation, Williamsburg, Virginia (United States), 22–26 Jun. 1987. Vol. 7A, pp. 821–830. Edited by D.D. Thompson and D.E. Chimenti, Plenum Press, 1988.