Evaluation of Stress Intensity Factor of 316 SS LN Circular Grid Plate Hardfaced with Colmonoy 5 for Various Loads

摘要

In sodium cooled fast breeder reactors, the high operating temperature necessitates hardfacing of grid plate to avoid galling of the base material. Nickel based cobalt-free alloy called Colmonoy-5 has been chosen as the hard facing material for the Prototype Fast Breeder Reactor (PFBR) grid plate. The grid plate (GP) which is a critical component made of SS316 that holds the core subassemblies are hard faced, to prevent galling caused by subassembly insertion/removal and erosion due to high sodium velocity at 670 K. Colmonoy 5 was hardfaced on circular grid plate along the annular groove by Plasma Transferred Arc Welding (PTAW). The process-induced residual stress generated due to difference in coefficients of thermal expansion between the deposit and substrate material was removed by annealing. In this paper, in order to evaluate Stress Intensity Factor (SIF) near the crack tip of the crack caused by the remote load or residual stresses generated due to thermal cycling owing to on/off of nuclear reactor, a grid plate model hard-faced with colmonoy 5 was prepared and then annealed to remove process-induced residual stress. Considering the plane strain condition to the same geometry of the model, a 3 mm crack was considered at the vertical interface between the steel and the colmonoy. By supporting the specimen on the left and right corners of the upper side, load was applied exactly on the opposite side of crack in the positive direction, simulating mode I loading. After loading the model and getting the solution, KI was obtained at the crack tip. This step was repeated for various loads to obtain the relationship between SIF and load for fracture characteristics.