Assessment of pipeline dent strain severity using surface interpolation

管道凹陷分析的当前趋势已经并且仍然将管道凹陷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陷深度的标准，原因在历史和研究中有充分的记载。然而，基于应变的凹陷严重性评估受到用于评估管道受影响区域中的应变分布的可用技术的限制，因为用于执行非线性有限元分析（FEA）的现有数值求解器是昂贵的并且计算要求高，并且代码中可用的封闭形式表达式在假设中被过度简化。在这项研究中，提出了一个数学模型的应变评估的凹陷管道。该模型采用三维三次三次样条函数进行凹痕应变严重性分析。这种新的方法离散的位移分量与凹痕的基础上的线弹性壳理论，开发一个连续的但可微的表面轮廓的凹痕。离散化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约束或释放基于应变的模型的自由度，并允许应变测量选择的灵活性。在这项研究中的第三个方向的列入允许的剪切应变分量的评价以前忽略了现有的分析模型。本提案的目的是调查由数学模型预测的应变与FEA预测的应变之间的相关性，从而表明在不诉诸FEA的情况下对凹陷管道进行更详细应变分析的可能性。最后，将根据该项目的结果制定一个确定凹痕挖掘优先级的标准。

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.