Design and analysis of rotating field eddy current probe for tube inspection

Steam generator unit in nuclear power plant comprise thousands of heat exchange tubes whereby heat from primary coolant is transferred to water circulating on the secondary side. A variety of tube degradation due to mechanical vibration and chemical interactions compromises the integrity of steam generator tubes. The rupture of these tubes may result in leakage of radioactive water to the environment. Periodic inspections aimed at timely detection and characterization of the degradation is a key element for ensuring tube integrity and safe operation of nuclear power plant. Eddy current testing has proved to be an effective technique to detect defects occurring in the tube wall. In the past two decades, three types eddy current probes developed for steam generator tube inspection include bobbin coil probe, rotating probe and array probe. Each of these probes has their own limitations.;The bobbin coil probe is insensitive to circumferential cracks, and rotating probe is slow and involves complex mechanical rotation whereas the array probe has poor resolution and high cost of instrumentation. This dissertation presents the design and validation of a new rotating field eddy current probe. The probe is composed of three phase rectangular windings and pickup sensor, that can be chosen to be a simple bobbin coil or a GMR array sensor placed at the probe center. The probe avoids mechanical rotation and has fast scan speed. The rotating field probe is sensitive to all orientation defects. The axial component of magnetic field along the tubing due to a defect is measured by the pickup sensor. The probe design and performance are evaluated using an experimental validated finite element model. A reduced magnetic vector potential formulation is used for simulating the different commercial probe as well as the proposed new probe design.;A probe prototype is built to validate the simulation results with respect to different defects. A parametric study is conducted using the model to optimize the design and evaluate its performance. An encircling rotating field eddy current probe utilizing similar principles is also studied in this research. A design of a rotating field probe that encircles a cylindrical sample is presented and studied. Differences in the performance in cases of magnetic and nonmagnetic tube materials are described. Initial results show the feasibility of rotating field probes to detect a variety of defect geometries.