Evaluation of the Failure of a Radioactive Waste Transfer Line Jacket

Radioactive wastes are confined in 49 underground storage tanks at the Savannah River Site. The waste is transported between tanks primarily via an underground transfer piping system. Due to the hazardous nature of the waste, the inner core stainless steel pipe is typically surrounded by a carbon steel pipe jacket, which provides secondary containment. Recently, several through-wall penetrations were discovered on a segment of one of the jackets. An evaluation was performed to verify the failure mechanism and to estimate the degree of damage that existed on the pipe segment. Failure analysis confirmed that pitting corrosion on the exterior of the pipe led to the through-wall penetration. Ultrasonic measurements were utilized to determine the remaining wall thickness in adjacent areas of the pipe. Based on these measurements, the degree of pitting and general corrosion was determined. Pit growth rate models were then developed to estimate the life expectancy of sections of the pipe that had not been excavated. The calculations indicated that the occurrence of through-wall penetrations in this jacket will begin to increase substantially in 12 years. Given that this pipe segment will be utilized beyond this time, short-term and long-term solutions to this failure were proposed. The short-term solutions focused on the repair or replace decisions that must be made to return the jacket to service as soon as practical. The long-term solutions focused on a broader strategy to address jacket integrity issues in the entire waste storage facility. These solutions included the evaluation of innovative remote inspection and repair techniques.