When Old Line Pipes Initiates Fracture in a Ductile Manner

This paper presents a procedure to determine the lowest temperature that a ductile fracture will initiate in old (or new) pipe that behaves in a brittle manner (by Charpy testing). Over the last decade, 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 where ductile fracture initiation occurs and relates that temperature back to Charpy impact data for X60 and lower grades, particularly for older vintage linepipe materials. The method involves a series of transition temperature shifts to account for thickness effects, strain-rate effects, and constraint effects to give a master curve of transition temperatures from Charpy data to through-wall-cracked or surface-cracked pipes (with various surface-crack depth 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. Conducting tests on 1927 and 1948 vintage line-pipe steels subsequently validated this method. In addition, data were developed on the 1927 vintage pipe material to assess the effect of the bluntness of a corrosion flaw on the lowest temperature where ductile fracture will still occur under quasi-static loading. An addition transition temperature shift occurs as a function of the bluntness of the flaw.