INSPECTION OF BURIED PIPING IN NUCLEAR POWER PLANTS -FIELD OBSERVATIONS AND CHALLENGES

The issues over the integrity of buried piping in Nuclear Power Plants (NPPs) have received significant attention over the past few years. These piping systems have been in operation for over 30 years. Leaks from buried piping have the potential to raise safety, radiological, environmental, and financial concerns. Buried piping are subject to degradation mechanisms from the outside (soil side) as well as from the inside (fluid side) and they are primarily protected from external corrosion by applying coating on the pipe and then using cathodic protection to protect any bare areas or holidays in the coating. However, over a period of time the coating may lose its integrity and fail to provide the protection for which it was intended. As this happens, the amount of cathodic current needed for adequate protection increases. In some instances, the coating will disbond from the pipe and shield the cathodic protection from the pipe surface. Because of the economic, environmental, and safety consequences of a failure, NPPs embarked on inspection programs to determine the pipe's condition and its suitability for continued service. This paper presents some of the observations made during the indirect and direct inspections of buried piping. In addition, the challenges encountered are reported.