Evaluation of the Growth and Stability of Stress Corrosion Cracks in Sensitized Austenitic Piping

This paper presents the results of a research program conducted to evaluate the behavior of stress corrosion cracks in sensitized austenitic piping exposed to high temperature, high purity oxygenated water. The program was directed toward the development of a predictive method which included a design margin assessment and an evaluation of crack growth leading to a predictive model. As part of the margin assessment, the program developed diagrams which predicted net section collapse as a function of crack size. Acceptance flaw sizes were then determined by applying a safety factor on the net section collapse condition. The growth behavior of stress corrosion cracks was assessed using laboratory test crack growth rate data coupled with linear elastic fracture mechanics. Knowing the initial flaw size, the crack growth rate data can be used to predict the final flaw size at the end of the next inspection period. Continued operation would be acceptable during this period if the final flaw size is less than the acceptance value. The method developed here can be applied using stress information available in ASME (American Society of Mechanical Engineers) Code piping stress reports and crack growth data presented here. The method developed can be used to establish an in-service inspection plan for power plants with cracked piping allowing continued plant operation. Example predictions for 4-in. (10.16-cm) and 24-in. (61-cm) pipe were made to demonstrate the methodology’s use.