Ductile fracture arrest methodology for current and future grades of linepipe steels

摘要

This paper summarizes a methodology for arrest of unstable axial ductile crack propagation established under prior work by the American Gas Association and recently used by TransCanada for assessment of new and future gas pipeline projects. The past ductile fracture methodologies generally involve using the Charpy V-notch test, but the test has proven to be unreliable for high toughness materials and for materials that have rising shelf energies. The methodology utilized the energy from a full thickness impact specimen, of which the DWTT is the most frequently used. Various modified notch specimens have been proposed in order to obtain the propagation energy component of the tests. Correlations between the Charpy test and the DWTT test allow for converting the DWTT propagation energy into a equivalent Charpy propagation energy for use in the existing ductile fracture equations. This paper discusses the methodology, shows differences with materials from different manufacturers, and explores the trends for higher strength materials.