Predicting the Brittle-to-Ductile Fracture Initiation Transition Temperature for Surface-Cracked Pipe From Charpy Data

Much work has been done to assess constraint effects on the crack-driving force for specimens and cracks in pipes. The material’s transition temperature where the fracture process changes from ductile tearing to cleavage fracture at crack initiation is affected by the constraint conditions, but is a material property that cannot be determined analytically. This paper presents a methodology to account for constraint effects to predict the lowest temperature for ductile fracture initiation and relates that temperature to Charpy impact data for typical ferritic pipe materials. It involves a series of transition temperature shifts to account for thickness, strain-rate, and constraint to give a master curve of transition temperatures from Charpy data to through-wall-cracked or surface-cracked pipes (with various a/t values) under quasi-static loading. These transition temperature shifts were based on hundreds of pipe tests and thousands of specimen tests over several decades of work by numerous investigators. It is equally applicable to ferritic nuclear pipe for Class 2, 3, or balance of plant piping, or for older linepipe materials. If found to be reasonable, then the procedure could be used in the ASME pipe flaw evaluation procedures as a screening criterion between LEFM and EPFM failure modes.