Nonlinear Buckling Performance Analysis of Carcass Layer in Flexible Riser Considering Processing Residual Stress

The flexible riser is a key component of deep-water oil and gas transportation systems. Within its multilayered construction, the carcass layer is the primary metallic load-bearing layer resisting external hydrostatic pressure. Its buckling failure directly compromises the overall structural integrity of the riser. This study numerically investigates the nonlinear buckling behavior of the carcass layer with simultaneous consideration of processing-induced residual stress and initial geometric imperfection. A simplified one-quarter circular model of the carcass layer was developed on the Abaqus finite-element platform, in which material nonlinearity, contact friction, and large-deformation effects were included; the model accuracy was verified. Initial ovality and processing residual stresses were introduced via modified keywords and predefined fields, respectively, to examine the evolution of the critical collapse pressure for straight and curved segments under different residual-stress directions. Results show that the critical load decreases monotonically with increasing ovality. Residual stresses further weaken structural stability, with circumferential residual stress exhibiting a stronger detrimental effect than axial residual stress. Finally, a Python scripting workflow was used to enable parameterized modeling and batch simulations in Abaqus, and a sensitivity study was performed on key cross-sectional parameters (L1, L2, L5, R1, A1, t). The thickness t has the most pronounced influence on the critical load, followed by L1 and L2, whereas increasing L5 reduces the buckling resistance. The findings provide guidance for manufacturing accuracy control and structural optimization of flexible riser carcass layers.