Analytical Approach for Buckling Resistance of UOE Linepipe With Orthogonal Anisotropy Under Combined Loading

UOE linepipes have orthotropic work hardening in which the longitudinal (L-) stress vs. strain (SS) curve is different from the circumferential (C-) one. The anisotropy is emphasized by the thermal aging during the anti-corrosion coating. However, there are few studies on the effect of the circumferential mechanical properties on the compressive strain limit required in strain-based design (SBD). This paper describes the combined effect of SS curves in L- and the C-direction on the buckling resistance using the newly developed yield function to model the orthogonal anisotropy. The coupon tests after thermal aging during the anti-corrosion coating indicate that the L-SS curve can maintain the round-house type while the long yield point elongation (YPE) appears on the C-SS curve. Using these mechanical properties, FE-models demonstrate that YPE in the C-direction reduces the compressive strain limit for pipes with high diameter/thickness (D/t) under high internal pressure. Hence, SS curves in the C-direction should be considered for more reliable prediction of the buckling resistance required in long distance gas pipelines.