Abstract: A process for using an eddy current probe to precisely locate the edges of a baffle plate or support plate which surrounds a tube of a heat exchanger is disclosed herein. The process generally comprises the steps of moving the eddy current probe through the interior of the tube in the vicinity of the plate with the axis of rotation of the coil oriented parallel to the longitudinal axis of the tube. The rate of change of coil impedance is monitored as a function of the position of the coil along the longitudinal axis of the tube. When the rate of change of current flow through the coil attains its first maximum, the mid-plane of the coil is parallel to the bottom edge of the plate. This process is particularly useful in implementing maintenance procedures wherein heat exchanger tubes are selectively expanded along certain portions of their longitudinal axes in order to eliminate or reduce unwanted clearance between the tubes and the bores in the support plates through which they extend.