1. A method of machine implemented analysis of eddy current test data recorded in quadrature channels at spaced data points as a probe is passed through the tubes of a heat exchanger, comprising the steps of: storing the eddy current data for the spaced data points in a data array in a programmed digital computer; operating the digital computer to examine the data in the array point by point to identify lobes; operating the digital computer to group the lobes into signatures; storing a set of rules in the digital computer for characterizing as a function of selected characteristics of said signatures, structural features surrounding the tubes and defects in the tubes; and operating the digital computer to apply said rules to said signatures to identify the structural features and defects and to generate an output identifying the structural features and defects identified.