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    Application of Maximum Load Toughness to Defect Assessment in a Ductile Pipeline Steel

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    It is generally considered that, when a material behaves in a fully ductile manner, the most accurate method of fracture analysis is that based on the R-curve/driving force concept. Other, simpler, methods involve the use of a single value of toughness, for instance, that at initiation of tearing or at the maximum load point determined on a suitable small-scale test piece. Maximum load toughness has been used extensively in conjunction with the crack tip opening displacement (CTOD) design curve assessment method. To assess its general applicability, the results from an experimental program involving burst tests, wide plate tests, and numerous small-scale tests on a ductile pipeline steel conforming to API 5LX 56 were analyzed by various methods. These included the CTOD design curve, the CEGB R6 method, the method of Kiefner et al for axial flaws in pipelines, together with a pseudo linear elastic fracture mechanics (LEFM) R-curve approach and the Paris stability analysis. Initiation toughness, maximum load toughness, and R-curves were all used as input, where applicable. It was found that the use of initiation toughness gave very conservative assessments, whereas the R-curve techniques were complex and not always conservative. Maximum load toughness with any of the relevant analyses gave conservative and simple assessments.


    ductile fracture, flaw assessment methods, initiation toughness, maximum load toughness, R, -curves, pipelines, axial flaws

    Author Information:

    Willoughby, AA
    The Welding Institute, Abington, Cambridge,

    Garwood, SJ
    The Welding Institute, Abington, Cambridge,

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP34278S