End Boundary Effects on Local Buckling Response of High Strength Linepipe

Abstract

In this paper, the significance of the length to diameter ratio (L/D) on the local buckling response was evaluated using continuum finite element modelling procedures. A numerical model was developed, using the finite-element simulator ABAQUS/Standard, to predict the local buckling and post-buckling response of high strength pipelines subject to combined state of loading. The numerical procedures were calibrated using test data from large-scale experiments examining the local buckling of high strength linepipe. The numerical model’s response was consistent with the measured experimental response for predicting the local buckling behavior well into the post-yield range. A parametric study was conducted to examine the significance of the linepipe L/D ratio with respect to the yield stress to ultimate stress ratio (Y/T) and hoop yield stress to longitudinal yield stress ratio or anisotropy factor (R). As the models with high L/D ratio exhibit global Euler-type response, a numerical algorithm was developed to calculate the local section moment response for the FE analysis. The analysis conducted provides insight on the significance of end effects on the local buckling response. There are questions on the approach taken by current industry practice with respect to establishing compressive strain limits for local buckling when using shorter linepipe segment lengths. The results from this study suggest end effects require assessment and potential mitigation.

Ovality of High-Strength Linepipes Subject to Combined Loads

“…Numerical modeling investigations, have indicated pipe segment lengths greater than 10 diameters would be sufficient to mitigate the end boundary conditions and mechanical response of an over-constrained system [12]. Other recent physical experiments and numerical simulations support this argument and have examined pipe segment lengths of 5 to 20 pipe diameters at [6,15,17].…”

“…Characteristics of the stress-strain relationship through the subyield plastic and transition regimes may be one of the factors accounting for the apparent dependency of compressive strain capacity on material grade and yield strength [4]. Studies conducted by the authors [12,13,15,19] have observed a relationship between peak moment (i.e. strength capacity) and material grade but not with compressive strain capacity (i.e.…”

“…Furthermore, previous studies have demonstrated the unrealistic requirements (i.e. imperfection amplitude and prescribed location) for imposing initial geometric imperfections within the 3.5D pipe segment length model to initiate local buckling response [12,13,15,19]. For longer pipe segment models (i.e.…”

“…Recent numerical studies have shown the importance of pipeline segment test length and corresponding boundary effects on the local buckling response of plain and girth weld pipe [12,13]. For shorter pipe segments, of length to diameter ratios of 3.5, end boundary conditions impose constraints on the pipe end section ovalization response and axial stiffness.…”

“…Some of these areas include parameter characterization and quantification on effects of capacity reduction associated with initial geometric imperfections of the pipe body, residual stress and geometric imperfections associated with girth welding processes, material anisotropic behavior and discontinuous yielding [6,12,13].…”