Nondestructive testing and evaluation of high pressure feed water heat exchanger tubes using differential-type bobbin coils and solid-state integrated GMR sensor array

摘要

Nondestructive examination and evaluation system for high pressure feed water heat exchanger tubes in nuclear power plant was developed. Differential-type bobbin coils made of copper wire are placed on both sides of GMR sensors arranged in a ring shape. If alternating current (AC) is applied to the bobbin coils, then an inductive current is occurred in circumferential direction of the tube to be examined. Under these conditions, eddy currents are generated around the defect. Because the timevarying magnetic field is distorted by eddy current that is generated around the defect, the shapes and dimensions of defect can be quantitatively evaluated with cylindrical arrayed GMR sensors. The result was verified by the artificial defects fabricated in a small diameter heat exchanger tube.