The equipotential switching array probed direct current potential drop (ESAP-DCPD) system has been developed to monitor on-line the initiation and growth of a crack in piping weldment. The new technology of equipotential establishment at all borderlines of a monitoring segment eliminates any significant current leakage to outside systems. The thermal fluctuation of DCPD signal has been suppressed by using an already established switching current method. The arrangement of an array probe surrounding the weldment was optimized by performing finite element analysis (FEA) of DCPD in such ways to improve its detectability for circumferential cracks. In order to verify the reliability and detectability of piping weld monitoring, artificial cracks introduced into a full-scale weldment mockup were monitored by using ESAP-DCPD in laboratory environments. Then experimental results were compared with FEA results for the mockup to show a good agreement. Therefore FEA can be used to design a field application system. In order to pursue a first-of-a-kind application in a nuclear power plant, a preliminary licensing basis has been developed through development of an initial 10 CFR 50.59 analysis, as described herein.
On-Line Monitoring of Environment-Assisted Cracking in Nuclear Piping Using Array Probe Direct Current Potential Drop
