L51845 Database of Mechanical and Toughness Properties of Pipe

 The lower-strength grades of steel used for transmission pipelines into the 60s were much like those used in other steel construction in that era. These steels gained strength by traditional hardening mechanisms through chemistry changes, largely involving carbon and manganese additions. Improvement of these grades, primarily through control of ingot chemistry and steel processing, became necessary when running brittle fracture was identified as a failure mechanism in gas-transmission pipelines in the late 50s. Eventually, this avenue to increasing strength was exhausted for pipeline applications because this approach causes increased susceptibility to hydrogen-related cracking mechanisms as strength increases. For this reason, modern steels differ significantly from their predecessors in several ways, with the transition from traditional C-Mn ferrite-pearlite steels beginning in the mid 60s with the introduction of high-strength-low-alloy (HSLA) steels.

This report presents the results of projects, PR-3-9606 and PR-3-9737, both of which were planned as multi-year projects. The first of these projects initially was conceived to provide broad evaluation of the fitness-for-service of wrinkle bends while the second was conceived to generate mechanical and fracture properties data for use in the integrity analysis of both the pipe body and weld seams in modern gas-transmission pipeline systems. As possible duplication between a joint industry project and the PRCI project became apparent, this project was scaled back to focus on properties of steels used in construction involving wrinkle bends. Consideration also was given to a more modern steel such as might be found in ripple bends, which are formed in bending machines that now have become widely used. The second project likewise was reduced in scope, with a focus on only the pipe body. Because both projects ended being centered on mechanical and fracture properties, both are presented in this combination report.