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

• Lock-in IR thermography was proposed to detect wall-thinned defects during normal NPP operation.
• A mock-up loop was constructed that contained artificially generated defects.
• The fluid inside the loop was maintained at a temperature similar to NPP operating conditions.
• The boundary of the wall-thinned defective part was clear from acquired images.

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.