环向加劲肋对海底管道屈曲性能影响的数值模拟研究

Numerical study on the effects of ring stiffeners on the buckling performance of subsea pipelines

海底管道担负着海上油气集输的重要使命,是海洋油气生产系统的生命线。海底管道在静水压力作用下产生的局部屈曲及其传播是设计时首要考虑的结构失效模式。增设环向加劲肋是有效提升海底管道抗屈曲性能的经济有效手段。本文基于有限元分析软件ABAQUS建立带环向加劲肋管道的有限元模型,系统分析环向加劲肋间距、高度和厚度3个参数对管道抗屈曲性能的影响,并将管道模型的数值模拟结果与试验结果进行对比分析,以验证该有限元模型的准确性。在此基础上,通过参数分析的方法,研究了环向加劲肋的间距、厚度和高度对带环向加劲肋管道抗屈曲承载力P_(cr)的影响,并提出了相关管道的极限屈曲载荷计算公式。研究结果显示:1)环向加劲肋间距、厚度、高度3个参数对管道抗屈曲承载力P_(cr)的影响相互关联,其中环向加劲肋间距对管道抗屈曲承载力P_(cr)的影响最为显著;2)管道抗屈曲承载力P_(cr)表现出与环向加劲肋间距成反比例的增长趋势;3)环向加劲肋的焊接会产生残余应力,从而减弱加劲肋对管道的加强效果,进而表明准确的有限元模型应考虑残余应力的影响;4)具有足够刚度的环向加劲肋可有效将局部屈曲行为控制在加劲肋之间,并改变管道的屈曲破坏模态,有效提升管道的抗屈曲承载力P_(cr);5)提出的管道抗屈曲承载力P_(cr)计算公式能较好地预测结果,可作为设置环向加劲肋管道的设计依据。

The subsea pipeline plays a pivotal role in transporting offshore oil and gas, and serves as a lifeline in the offshore oil and gas production system. The local buckling and its propagation of subsea pipelines under hydrostatic pressure are the primary structural failure mode for the pipeline design. The use of ring stiffeners is an economical and effective means to improve the buckling resistance of subsea pipelines. In this paper, a Finite Element(FE) model of a pipeline with or without the ring stiffener was established in the FE software ABAQUS to systematically investigate the effects of the spacing, height and width of the ring stiffener on the ultimate buckling performance of the pipe. The simulation results including ultimate load and failure mode were subsequently compared with their corresponding testing results to validate the accuracy of the FE model. A series of parameter analyses were conducted to investigate the effects of the spacings, thickness and height of the ring stiffener on the critical buckling pressure P_(cr) of the pipeline strengthened with ring stiffeners, thereby proposing a formula with regard to the critical buckling pressure P_(cr) of the pipe with ring stiffeners. The relevant analysis results show that: 1) The effects of the spacing, thickness and height of ring stiffener were found coupled on the critical buckling pressure P_(cr) of pipeline, with the most significant and effective effect on the enhance of the critical buckling pressure P_(cr) due to closer spacing of ring stiffener;2) An inversely increasing trend was observed for the critical buckling pressure P_(cr) of the pipeline with the decline in the spacing of ring stiffeners;3) A significant effect was found on undermining the strengthening effect of the ring stiffener on critical buckling pressure P_(cr) of the pipe due to the presence of residual stress produced in the welding operation at the connection between ring stiffener and pipe, which indicates that the effect of residual stress should be considered in an accurate FE model of the pipe with ring stiffeners;4) The ring stiffener with sufficient rigidity could effectively restrain the local buckling behavior of the pipe between adjacent stiffeners, and lead to a change in the buckling mode and an effective enhance in the critical buckling pressure P_(cr) of the pipe;5) the critical buckling pressure P_(cr) of the pipeline could be accurately predicted with the proposed formula based on the above findings, an agreement that indicates that the proposed formula in this paper is appropriate as a design basis for pipes with ring stiffeners.