Corrosion deterioration decision method null of two layer metal

摘要

PURPOSE:To judge the corrosive deterioration of a two-layer metal wire material wherein the periphery of a core wire is coated with a different kind of a metal such as a zinc plated steel stranded wire by individually detecting the residual amounts of the core wire and the coating layer after corrosion. CONSTITUTION:When a zinc plated steel stranded wire is subjected to an eddy current flaw detection test, the phase detection output thereof linearly changes on the two-dimensional plane shown by a phase and amplitude in directions respectively different at the time when only a zinc plating layer reduces and at the time when only a steel stranded wire reduces. Therefore, when only the phase component in the direction crossing those straight lines at a right angle is taken out from the output of a detection coil, phase detection is performed in the phase of the direction capable of detecting the volume change of one metal without being affected by the volume change of the other metal to individually detect the residual amounts of the respective metals.