Assessment of pipeline dent strain severity using surface interpolation

由于历史和研究的原因，目前管道凹坑分析的趋势已经并仍在将管道凹坑完整性管理方案的重点转向局部应变分布，而不是传统的基于凹坑深度的标准。然而，由于用于执行非线性有限元分析(FEA)的现有数值求解器昂贵且计算要求高，并且代码中可用的封闭形式的表达式在假设中过于简化，因此基于应变的凹坑严重程度评估受到用于评估管道受影响区域中的应变分布的现有技术的限制。在这项研究中，提出了一个数学模型来评估凹陷管道的应变。该模型采用三维三次三次样条函数进行凹陷应变严重性分析。这种新方法基于线弹性壳理论对凹坑的位移分量进行离散化，以得到凹坑的连续但可微的表面轮廓。离散化的位移分量创建了一个平台，该平台为操作员提供了从基本假设中约束或释放基于应变的模型的自由，并允许在选择应变测量时的灵活性。在这项研究中包括第三个方向，可以评估以前在现有分析模型中被忽略的剪切应变分量。这一建议的目的是研究数学模型预测的应变与有限元预测的应变之间的相关性，从而表明对凹陷管道进行更详细的应变分析的可能性，而不必求助于有限元分析。最后，将根据该项目的结果制定确定凹陷挖掘优先顺序的标准。

Current trends in the analysis of dents in pipeline has been and is still turning the focus of pipeline dent integrity management schemes on the localized strain distribution rather than the traditional dent depth based criterion for reasons well documented in history and research. The strain based evaluation of dent severity however is limited by the available techniques for evaluating the strain distribution in affected regions of the pipeline as the existing numerical solvers used to perform nonlinear finite element analysis (FEA) are expensive and computationally demanding and the available closed form expressions in the codes are over simplified in assumptions. In this study a mathematical model is proposed for the strain evaluation of dented pipelines. The model employs the use of three dimensional third order cubic spline functions for performing dent strain severity analysis. This novel approach discretizes the displacement components associated with the dent based on the linear elastic shell theory to develop a continuous yet differentiable surface contour of the dent. The discretized displacement components create a platform that provides operators with the liberty to constrain or release the strain based model from underlying assumptions and allows for flexibility in the choice of the strain measure. The inclusion of the third direction in this study allows for the evaluation of the shear strain components previously neglected in existing analytical models. The objective of this proposal is to investigate the correlation between the strains predicted by the mathematical model and those predicted from FEA thus indicating the possibility of performing a more detailed strain analysis on dented pipelines without having to resort to FEA. Finally, a criterion for prioritizing dent digs will be developed based on the results of this project.