Assessment of pipeline dent strain severity using surface interpolation

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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.