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A Magnetic Flux Leakage NDE System for CANDUR Feeder Pipes

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A Magnetic Flux Leakage NDE System for CANDUR Feeder Pipes A Magnetic Flux Leakage NDE System for CANDU R Feeder Pipes by Thomas Don Mak A thesis submitted to the Department of Physics, Engineering Physics & Astronomy in conformity with the requirements for the degree of Master of Applied Science Queen’s University Kingston, Ontario, Canada March 2010 Copyright c Thomas Don Mak, 2010 Library and Archives Bibliothèque et Canada Archives Canada Published Heritage Direction du Branch Patrimoine de l’édition 395 Wellington Street 395, rue Wellington Ottawa ON K1A 0N4 Ottawa ON K1A 0N4 Canada Canada Your file Votre référence ISBN: 978-0-494-65131-5 Our file Notre référence ISBN: 978-0-494-65131-5 NOTICE: AVIS: The author has granted a non- L’auteur a accordé une licence non exclusive exclusive license allowing Library and permettant à la Bibliothèque et Archives Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par télécommunication ou par l’Internet, prêter, telecommunication or on the Internet, distribuer et vendre des thèses partout dans le loan, distribute and sell theses monde, à des fins commerciales ou autres, sur worldwide, for commercial or non- support microforme, papier, électronique et/ou commercial purposes, in microform, autres formats. paper, electronic and/or any other formats. The author retains copyright L’auteur conserve la propriété du droit d’auteur ownership and moral rights in this et des droits moraux qui protège cette thèse. Ni thesis. Neither the thesis nor la thèse ni des extraits substantiels de celle-ci substantial extracts from it may be ne doivent être imprimés ou autrement printed or otherwise reproduced reproduits sans son autorisation. without the author’s permission. In compliance with the Canadian Conformément à la loi canadienne sur la Privacy Act some supporting forms protection de la vie privée, quelques may have been removed from this formulaires secondaires ont été enlevés de thesis. cette thèse. While these forms may be included Bien que ces formulaires aient inclus dans in the document page count, their la pagination, il n’y aura aucun contenu removal does not represent any loss manquant. of content from the thesis. Abstract This work examines the application of different magnetic flux leakage (MFL) inspec- tion concepts to the non destructive evaluation (NDE) of residual (elastic) stresses in R CANDU reactor feeder pipes. The stress sensitivity of three MFL inspection tech- niques was examined with flat plate samples, with stress-induced magnetic anisotropy (SMA) demonstrating the greatest stress sensitivity. A prototype SMA testing sys- tem was developed to apply magnetic NDE to feeders. The system consists of a flux controller that incorporates feedback from a wire coil and a Hall sensor (FCV2), and a magnetic anisotropy prototype (MAP) probe. The combination of FCV2 and the MAP probe was shown to provide SMA measurements on feeder pipe samples and predict stresses from SMA measurements with a mean accuracy of ±38 MPa. i Acknowledgments First and foremost I would like to thank my supervisor, Dr. Lynann Clapham, for presenting me with this wonderful opportunity. Her guidance and expertise were greatly appreciated. This work would have been far less interesting and enjoyable without the assistance of Dr. Steven White. He acted as a teacher from the moment I began working under him as a summer student in 2006, and he provided invaluable assistance in all aspects of this project from its conception, from theory to design, data acquisition and signal processing. I would also like to thank all members of the AECL Inspection Monitoring and Dynamics Branch, in particular H´el`eneH´ebert. She helped organize meetings with AECL and provided helpful advice and encouragement. Thanks are due to Dirk Bouma, who was consulted frequently during the design of the first flux control system (FCV1), as well as Gary Contant and Chuck Hearns for their help and supervision in the machine shop. I also thank Pat Wayman for all her help during all phases of this project. Several students provided valuable assistance: Ben Lucht helped with LATEX and R MATLAB , and Davin Young spent many hours in the machine shop building probe components. ii Table of Contents Abstract i Acknowledgments ii Table of Contents iii List of Tables v List of Figures vi Chapter 1: Introduction . 1 R 1.1 CANDU Feeder Pipes . 2 1.2 A Brief Introduction to Magnetic Circuits and Magnetic Flux Leakage Inspection . 5 1.3 Thesis Scope and Objectives . 7 1.4 Organization of Thesis . 8 Chapter 2: Theory and Background . 10 2.1 Stress and Strain . 10 iii 2.2 Maxwell’s Equations and The Quasi-Static Case . 15 2.3 Magnetic Materials . 16 2.4 Magnetic Methods of Stress Measurement . 29 Chapter 3: Flux Control Systems . 39 3.1 Negative Feedback Control and Operational Amplifiers . 40 3.2 Magnetic Flux Transducers . 42 3.3 Component Selection . 47 3.4 White’s Flux Control System (FCS) . 49 3.5 Flux Control Version 1 (FCV1): Hall Sensor Feedback . 51 3.6 Flux Control Version 2 (FCV2): Hall Sensor and Coil Feedback in Combination . 60 Chapter 4: Magnetic Stress Detectors . 67 4.1 Test Sample and the Single Axis Stress Rig (SASR) . 69 4.2 Detectors, Data Acquisition and Data Analysis . 72 4.3 Experimental Procedures for Testing and Comparison of the Probe Systems . 75 4.4 Detector Results and Analysis . 76 4.5 Selected Detector . 90 Chapter 5: Proposed Design: MAP Probe . 91 5.1 Magnetic Anisotropy Prototype (MAP) Probe . 92 iv 5.2 MAP Probe Testing with SA-106 Grade B Pipe . 96 Chapter 6: Summary and Conclusions . 107 6.1 Flux Control Systems . 107 6.2 Magnetic Stress Detectors . 108 6.3 Proposed MAP Probe Design . 109 6.4 Recommendations for Future Work . 110 Bibliography . 113 Appendix A: FCV1 Details . 118 Appendix B: Skin Depth . 120 v List of Tables 3.1 Excitation and monitor coil properties. Inductance values were recorded on-sample at 100 Hz. The monitor coil was wound around one of the core’s poles, making its area the same as the pole area. 53 3.2 PCI-6229 I/O assignment and terminal configuration for FCV1. Ter- minal configurations use the following abbreviations: referenced single- ended (RSE), non-referenced single-ended (NRSE), differential (DIFF). For additional information on terminal configurations see [29]. 53 3.3 PCI-6229 I/O assignment and terminal configuration for FCV2. 64 5.1 MAP probe properties. Feedback and excitation coils were wound on an external forming rig, which is why their area differs from the Supermendur core footprint. 95 vi List of Figures R 1.1 A simplified sketch of a CANDU 6 reactor face. 3 1.2 A comparison of magnetic and electric circuits. 6 2.1 The stress tensor for an element of a continuous structure in Cartesian coordinates. 11 2.2 Residual stress formation in a bent beam. 13 2.3 Ferromagnetic domain structure. 18 2.4 A typical magnetization hysteresis loop for a ferromagnetic sample starting with zero magnetization. 19 2.5 A schematic of four magnetic domains aligned along the ¡100¿ direc- tions of Fe. 20 2.6 Demagnetizing field lines for: a) a single domain, b) two opposing domains separated by a 180◦ wall, and c) four domains separated by 90◦ and 180◦ walls. 24 2.7 Magnetostriction of a material with positive λs. 25 2.8 The two types of magnetoelasticity: magnetostriction and the Villari effect for a material with positive λs................... 26 2.9 The magnetization processes for samples with aligned and misaligned auxiliary fields and preferred crystalline axes. 27 vii 2.10 A simplified Barkhausen noise apparatus. 31 2.11 A bandpass filtered Barkhausen noise spectrum taken from 3 kHz to 600 kHz. 32 2.12 A polar plot of angular MBN energy measurements. 32 2.13 The application of magnetic flux leakage inspection in crack and cor- rosion detection. 34 2.14 The MFL signal from a segment of SA106-B schedule 80 pipe (a) ref- erence measurement and (b) after the introduction of residual stresses through a localized impact. Maxima correspond to red and minima correspond to blue, but no further colour scale information is available. 34 2.15 The rotation of the magnetic field just outside the sample (B~ out) rela- tive to the magnetic field within the sample (B~ in) when µ2 > µ1. 36 2.16 The orientation of B~ in and B~ out relative to the excitation core. 37 3.1 The components of a closed-loop control system shown in a block dia- gram. 41 3.2 The feedback system components contained within an op-amp. 43 3.3 The Hall effect for a Cartesian coordinate system. 45 3.4 A sketch of White’s FCS. 50 3.5 A simplified version of FCV1. 52 3.6 Hall voltage (VH ) and excitation current (Iex) for a sinusoidal reference voltage. 55 3.7 FCV1 response to a DC reference voltage of Vref = 0. 56 3.8 Monitor coil voltage Vmc boosts the noise amplitude relative to the excitation field. 58 viii 3.9 A simplified version of FCV2. 61 3.10 An electrical schematic of FCV2 showing the feedback system and the Hall sensor current source. 63 3.11 The magnetic fields measured by the Hall sensor and feedback coil in FCV2. 66 4.1 The three detector configurations used with the prototype excitation core. 68 4.2 The mild steel plate used to test different detector configurations. 70 4.3 A schematic of the single axis stress rig used to introduce tensile stress in the flat plate sample. 71 4.4 An assembled probe showing a detector mount assembly attached to the connector brace of the excitation core.
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