Sensitivity analysis of variable reluctance probe for steam generator tubing inspection

A major problem in nuclear power plant steam generators is the denting of tubes due to the corrosion of the tube support plate in the crevice gap adjacent to the tube. An early detection of accumulation of the corrosion product (magnetite) in the crevice gap would help avoid squeezing and denting of tubes by allowing timely chemical cleaning of the unit. This paper describes the application of a simple dc variable reluctance probe to the problem of crevice gap characterization and the selection of optimum sensor location (e.g., Hall transducer) on the probe body for maximum sensitivity. A computer model based on the finite element analysis technique has been employed in the sensitivity analysis. These studies show that a Hall transducer should be placed either at the outer edge of the trailing end or at the inner edge of the leading end of the probe.