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ACCURACY ASSESSMENT OF A THREE-DIMENSIONAL STRAIN-BASED MODEL FOR DENT ANALYSIS OF PIPES

  • Author / Creator
    Li, Yueying
  • Pipelines are the safest and most efficient way to transport oil and gas products throughout the world. Thus, pipelines have to traverse long distances and are typically buried underground which are susceptible to damages with use. Potential threats to the integrity of a pipeline include metal loss, cracking, dents, or the interaction of any of these. Among them, dents, defined as permanent inward plastic deformations localized in the pipe wall, can occur due to external impact, such as strike by construction equipment or settlement over rocks. The dent could further cause coating damage and in turn accelerate growth of corrosion or make the pipe more susceptible to cracking in the deformed area. It becomes necessary to assess the severity of dents in order to prioritize resource allocation in implementing management strategies. The Canadian pipeline code, CSA Z662-16, specifies that plain dents with depth greater than 6% of the nominal pipe diameter should be excavated and repaired. Because of the geometry, dents associated with localized strain and stress distribution have a greater potential to form and propagate cracks under cyclic pressurization when a pipeline is in operation. This is why they are of greater concern as a dent might fall below the codified deformation limits while violating the localized plastic strain or stress limits. As an alternative to the traditional depth-based criteria, the American Society of Mechanical Engineers Standard for gas pipelines, ASME B31.8-16, presents a set of non-mandatory analytical equations to predict the maximum strain in dents. More recently, numerical modeling via finite element analysis (FEA) has been proposed in literature as an accurate dent-assessment technique. In-line inspection (ILI) tools can take readings of the inner diameter of the pipe and indicate the location, shape, and size of dents. However, there is no universal dent assessment criterion that can take all dent features into account. The challenge now facing pipeline operators is that a large number of dents are being reported by ILI tools. Although FEA can model the full geometry of the dents and pipes, it is impossible to process large numbers of dents. Recently, the authors’ research group developed a robust but much simplified analytical model to evaluate the strains in dented pipes based solely on data obtained from inline inspection devices. When the strain distribution predicted using the analytical model is benchmarked against the strains by nonlinear FEA they showed a good agreement with certain error. The procedure, however, predicts more conservative results in terms of the maximum equivalent plastic strain (PEEQ). In order to estimate the accuracy in the recently developed model, a series of nonlinear FEA pipe indentation simulations were conducted using the finite element analysis tool, ABAQUS and compared with the analytical prediction. Recognizing the inherent error in the analytical model for dent strain assessment, machine learning techniques e.g., Gaussian Process Regression (GPR) and random forest (RF), was used for the accuracy assessment of the developed analytical model, quantifying the error in comparison with the FEA in terms of the maximum PEEQ. By varying the dent depth and the indenter radius, a model that quantifies the error inherent in the analytical model was developed. The proposed error model and the original analytical model along with the accuracy of the error prediction can be utilized to rapidly determine the severity of a dent.

  • Subjects / Keywords
  • Graduation date
    Spring 2021
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-fvh7-2b37
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.