On-power detection of wall-thinned defects using lock-in infrared thermography

Abstract

Recently, nuclear power plants (NPPs) have been using ultrasonic testing (UT) to inspect the pipes of secondary piping systems. However, UT is not suitable for measuring wall-thinned defects in small-diameter pipes and requires a long period of time to acquire analysis results. In addition, it is less reliable when inspecting small-diameter piping, and it is almost impossible to inspect defects during NPP normal operation. Therefore, UT is not reliable for detecting wall-thinned defects in the small-diameter pipes of NPPs during normal operation. In this study, we developed a lock-in infrared (IR) thermography technique to detect wall-thinned defects in the small diameter pipes of a NPP's secondary systems during normal operation. For experiments, a mock-up loop was constructed that contained artificially generated defects. The fluid inside the loop was maintained at a temperature similar to the operating conditions of a NPP. Based on the results of experiments where lock-in IR thermography was applied, it is expected to be possible to detect wall-thinned defects in piping during normal operation, shorten the maintenance time of NPPs, and improve the work efficiency of the inspector.