A New Material Characterization Approach for Evaluating the Deformational Capacity of Onshore Pipelines

• Author / Creator

  Ndubuaku, Onyekachi H.

• The buckling instability phenomenon in shell structures is inherently influenced by a variety of parameters which may exhibit direct nonlinear relationships with the resultant stress and consequent deformation in the structure, as well as complex interrelationships, under various loading combinations. Hence, a computerized simulation of complex nonlinear mechanics problems, such as shell buckling, is often required for predicting the deformational behavior of cylindrical shell structures by means of numerical optimization methods. Notwithstanding the numerous advantages of numerical simulation, semi-empirical derivation of constitutive mathematical models for predicting the deformational response of shell structures is usually fraught with inadequacies due to improper characterization of the material stress-strain relationship and consequent misrepresentation of the strain-hardening behavior. A simple and versatile stress-strain model was therefore developed as an essential component of this research for accurate parameterization of the stress-strain behavior of a wide range of metallic materials over the full range of strains, including materials with a well-defined yield point and extended yield plateau. The applicability of the developed stress-strain model was validated using experimental data from tensile coupon tests of various standard pipeline steels and other metallic materials. Preliminary studies, to show the adaptation of the material model to shell stability analysis, was also performed on uniformly-compressed simply-supported flat plated FE models and material curve shape variations were observed to play a pivotal role in the load-deformation response. The buckling behavior of thin-walled cylindrical shells subjected to various loading conditions was numerically evaluated using a computerized finite element (FE) simulation program, ABAQUS CAE. Extensive parametric analysis was conducted based on the main factors that influence the buckling response of cylindrical-shell structures, i.e. dimensional properties, loading conditions, material grade, and strain-hardening properties. Nonlinear multiple regression techniques were employed, using a powerful general-purpose computational software package (Wolfram Mathematica), to derive the coefficients of several constitutive nonlinear mathematical expressions, developed as handy design tools for estimating the critical limit strain (CLS) in onshore steel pipelines. The strain-hardening properties of the material stress-strain curve were incorporated into the constitutive equations based on the shape constants of the newly-developed stress-strain model. The semi-empirical models were developed according to two material-type classifications (yield-plateau type and round-house type) of the stress-strain curves of pipeline steels. Excellent goodness-of-fit with the critical limit strains obtained from the numerical finite element simulation was obtained for all the developed semi-empirical models. Good alignment with the trends of data obtained from full-scale experiments of pipe segments was also illustrated using the developed semi-empirical equations.

• Subjects / Keywords

  • Finite element analysis
  • Pipeline
  • Critical limit strain
  • Product-log function
  • Local buckling
  • Deformational capacity
  • Nonlinear multiple regression
  • Stress-strain model
  • Semi-empirical model

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-38cj-3035

• License

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