Fracture Mechanics and NDE: The Keys to Failure Prevention

This paper focuses on the evolutionary steps in both fracture mechanics and NDE that have led to a better understanding of how failure prevention programs may be constructed to achieve the best balance of effectiveness and cost. Workmanship standards for weld imperfections that are embodied in most construction codes are contrasted with fitness for service methods for flaw acceptance that require more knowledge about the uncertainty in flaw characterization. The role of fracture mechanics in providing a yard stick for inspection programs is discussed and the concept of Tolerable Flaw Diagrams (TFD) is outlined. The use of fracture mechanics as a tool to define NDE limits for high asset value pressure vessels and piping is described in relation to several examples including: the evaluation of fitness for service of cracked chemical plant pressure vessels and water wall boiler tubes. Probabilistic methods to prioritize the emphasis that should be placed on the quality of inputs to a failure prevention program for nuclear plant steam generator tubes degraded by corrosion are also discussed.