eddy current method for the study of stress corrosion cracking in austenitic components and device for implementing the procedure

摘要

In an eddy-current method for studying the corrosion depth associated with stress corrosion cracking in austenitic components, the impedance change of a flat sampling coil is evaluated both at a first low frequency in the range of less than 30 kHz and at a second, considerably higher frequency in the range of 2 MHz. In each case, compensated summed signals are generated, the low-frequency summed signal being rectified phase-independently in order to generate a signal which corresponds to the sum of the actual coil lift and the corrosion depth. The high-frequency summed signal is rectified with the aid of a phase-sensitive detector in such a way that the corrosion signal contained therein is suppressed and a lift signal is generated which is associated with the actual coil lift. The corrosion depth is determined by subtraction of the second signal from the first signal.