Large-diameter thick-walled steel pipes during their installation in deep-water are subjected to external pressure, which may trigger structural instability due to pipe ovalization, with detrimental effects. The resistance of offshore pipes against this instability is affected by local geometric deviations and residual stresses, introduced by the line pipe manufacturing process. In the present paper, the JCO-E pipe manufacturing process, a commonly adopted process for producing large-diameter pipes of significant thickness, is examined. The study examines the effect of JCO-E line pipe manufacturing process on the external pressure resistance of offshore pipes, candidates for deepwater applications using nonlinear finite element simulation tools. The cold bending induced by the JCO forming process as well as the subsequent welding and expansion (E) operations are simulated rigorously. Subsequently, the application of external pressure is modeled until structural instability (collapse) is detected. Both the JCO-E manufacturing process and the external pressure response of the pipe, are modeled using a two-dimensional (2D) generalized plane strain model, together with a coupled thermo-mechanical model for simulating the welding process.
Large-diameter steel pipes, fabricated through the spiral-welding manufacturing process, are extensively used in onshore pipelines for the transmission of energy (hydrocarbon) and water resources. However, their use in demanding applications, such as geohazard areas or in offshore applications has been very limited. Safeguarding the structural integrity in such areas of those pipes requires an efficient strain-based design framework. Bending deformation capacity in the presence of internal pressure is the major loading case under geohazard actions, whereas external pressure capacity governs the mechanical design in moderate-deep offshore applications. To predict accurately the structural performance of spiral-welded pipes, the coldbending manufacturing process should be taken into account. In the present paper, numerical models are developed simulating both the cold-bending process (decoiling and spiral bending) and the structural response of the pipe subjected to the loading conditions under consideration.The numerical modes have been verified against experimental results of spiral pipes conducted in the framework of a European research project. A parametric analysis is also conducted to examine the effect of spiral cold forming process on the structural behavior of spiral welded pipes. The results from the present study indicate that spiral-welded pipes can sustain significant amount of bending deformation and external pressure, in favor of their use in demanding onshore and moderately deep offshore pipeline applications.
Thick-walled steel pipes during their installation in deep water are subjected to combined loading of external pressure and bending, which may trigger structural instability due to excessive pipe ovalization. In the case of reeling installation method, prior to deep-water installation the pipe is subjected to cold forming associated with strong cyclic bending on the reel, resulting in the development of initial ovalitization and residual stresses, which may affect the pipe structural performance. Using advanced material models and finite element tools, the present study examines the effect of cyclic loading due to reeling on the mechanical behavior of thick-walled seamless steel pipes. In particular, it examines the effects of reeling on crosssectional ovalization and the corresponding material anisotropy and, most importantly, on pipePage 2 of 36 resistance against external pressure and pressurized bending. The results show that cyclic bending due to the reeling process induces significant anisotropy and ovalization on the pipe. It is also shown that the mechanical resistance of reeled pipes is lower than the resistance of nonreeled pipes, mainly because of the resulting cross-sectional ovalization at the end of reeling process.
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