Fracture Toughness Behavior of Complex Cracks in Dissimilar Metal Welds

Abstract

Currently, J-estimation scheme procedures to predict the load-carrying capacity of idealized circumferential through-wall cracks in nuclear grade piping materials employ analytical or numerical procedures coupled with the fracture toughness of the material to predict the pipe response. However, with the advent of primary water stress corrosion cracking (PWSCC), complex-shaped cracks occur in dissimilar metal (DM) welds. These welds consist of a nickel-based weld joining stainless steel and carbon steel base metals. The NRC Office of Nuclear Regulatory Research (RES) is conducting a program to investigate the behavior of circumferential through-wall and complex cracks in DM welds. In a prior paper, a series of full-scale pipe bend and laboratory-sized fracture experiments were documented. Initial analyses of those test results suggest that reasonable prediction of through-wall crack response is obtained from typical J-estimation scheme procedures using the weld toughness from a compact tension (CT) specimen and the appropriate material strength. In addition, the J-R curves from the through-wall cracked pipe tests, calculated using published η-factor solutions and numerical techniques, were very similar to the CT J-R curves. In this paper, the fracture toughness for the circumferential complex cracked experiments, which was developed from a modified η-factor solution, is presented. These results are compared to the CT and through-wall crack pipe J-R curve results. In addition, predictions of load carrying capacity using the complex crack J-R curve and through-wall crack J-estimation schemes are presented and illustrate the need for the development of a complex crack J-estimation scheme. To support this development, a net-section collapse solution and a modified K-solution is presented. Finally, the need for additional work to generalize the elastic solution and its incorporation into a closed-form J-estimation scheme is discussed.