The Impact of FEA Modeling Techniques for Level 3 Dent Engineering Critical Assessment: Shell Vs. Solid Elements

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Abstract Engineering Critical Assessments (ECA) is crucial to evaluating the fitness for service of pipeline dents to comply with regulatory standards such as US CFR 49 part 192.712(c) and Canada CSA Z662 clause 10.10.4. For dents requiring a level 3 assessment, finite element analysis (FEA) is often employed to evaluate complex dent features categorized from in-line inspection (ILI) or direct examination of the pipeline. Various analysis techniques and element types exist within FEA for performing level 3 dent assessments. The appropriate analysis technique and corresponding element types (i.e., shell or solid elements) are often chosen by balancing the dent ECA’s complexity with computational accuracy and time. Shell elements are more computationally efficient than solid elements, however, the through-thickness stress distribution is more accurately captured with solid elements. If computational time is of little concern, then solid elements are typically employed to obtain an accurate representation of the stress/strain distributions in and around the dent feature for further engineering assessment once FEA is completed. However, the nature of dent ECA rarely affords an assessment schedule with such a flexible time constraints. For instance, when the dent interacts with other complex deformation features such as metal loss, solid elements account for the local metal loss feature to achieve the most accurate results. As such, this study will compare the differences in using shell vs. solid elements for a dent ECA for plain dents using the same idealized indenter. Variations in the stress/strain results along with overall differences in the calculated remaining life of the feature will be assessed as a function of the solver time. The goal of the study is to provide guidance on how and to what extent the element type can affect the overall conclusions of two different element types of dent ECA.