Assessment of pipeline dent strain severity using surface interpolation

由于历史和研究的原因，目前管道凹痕分析的趋势一直是并且仍然是将管道凹痕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痕深度的标准。然而，现有的用于非线性有限元分析（FEA）的数值求解器价格昂贵，计算量大，且现行规范中的封闭形式表达式在假设上过于简化，因此基于应变的凹痕严重程度评估受到现有管道受影响区域应变分布评估技术的限制。本文提出了一种凹痕管道应变评估的数学模型。该模型采用三维三阶三次样条函数进行凹痕应变严重程度分析。该方法基于线弹性壳理论对与凹痕相关的位移分量进行离散化，得到凹痕的连续可微表面轮廓。离散位移组件创建了一个平台，为操作人员提供了自由约束或释放基于基本假设的应变模型，并允许灵活选择应变测量。本研究中包含的第三个方向允许评估剪切应变分量，以前在现有的分析模型中被忽视。本文的目的是研究数学模型预测的应变与有限元分析预测的应变之间的相关性，从而表明不必借助有限元分析就可以对凹陷管道进行更详细的应变分析的可能性。最后，将根据该项目的结果制定凹痕挖掘优先次序的标准。

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.