Highly pressurized pipelines crossing harsh environments need to have two chief materials properties; they should have high strength in transverse direction to resist high operating pressers; and high deformability in the longitudinal direction to accommodate externally induced deformations. Pipeline producers try to deal with this dual demand in their high strength steel (HSS) linepipe products by enhancing the yield strength in the transverse direction and maintaining deformability in the longitudinal direction. This practice results in significant level of anisotropy in yielding and early plastic regions. The effects of material anisotropy on complex pipeline limit states such as local bucking is not fully understood. This paper presents the results of a numerical study on the effects of material anisotropy on the buckling response of HSS pipes. The effects of operating pressure, diameter-to-thickness ratio, material grade, strain hardening and the ratio of longitudinal-to-transversal yield strength were taken into account. Combined (isotropic-kinematic) hardening material modeling technique — previously introduced by the authors — was employed in this study. The results of this study are presented in several graphs showing the variation of the critical buckling strain versus the level of material anisotropy of HSS pipes with different geometry, material and operation conditions. These results provide an insight into the effects of material properties on the buckling resistance of pipes, especially when anisotropy is present.

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