Line pipes are the most common structural system employed to transport crude and its derivatives for long distance at high-pressure settings to ensure rapid mobility and safe delivery. Even though being one of the most reliable and economical feasible methods, pipelines are usually subjected to global plastic strains with potential catastrophic effects on ductile crack initiation and propagation. Fracture initiation in metals is generally carry out on crack-free specimen geometries covering a well-defined state of stress domain that includes axisymmetric tension-compression, generalized shear and tension plane strain loading modes. On the other hand, fracture propagation in thick components, such as standard fracture mechanics configurations, exhibits a highly constrained stress level at the crack-tip, which differs strongly with the level of triaxiality developed in regular specimens used for initiation characterization. One of the common assumptions done in Engineering Critical Assessment (ECA) procedures and standard codes to assess criticality of initial defects is that the metallic material plastic flow can be well represented by the von Mises yield function for even large plastic deformations. This is due to during experimental material characterization coupons are directly extracted along the orientation (transverse or longitudinal) of interest from the pipe section and thus it is treated as isotropic. This factor may limit tremendously the applicability of the ECA for a more general loading case scenario, where the criticality of the initial crack is required. In this exploratory study, a X65 seam weld pipeline steel is investigated by considering the effect of anisotropy on plasticity and fracture response of bi-axial loading pipes having different crack lengths, diameter sizes and internal hydrostatic pressures.           


Anisotropy Effect on Ductile Crack Growth of Pressurized Pipes Under Fully Bending Moment

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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