A Novel Approach to the Strain Based Analysis of Dented Pipelines

• Author / Creator

  Okoloekwe, Chike P

• Pipelines form an integral component of the distribution network of oil and gas products, which have to be transported from production sites to markets far off where there is need for them. Pipelines thus have to traverse long distances and as any other structure are susceptible to damages with use. A common cause of damage is the mechanical damage in pipeline in the form of dents, which are caused by a host of factors ranging from, but not limited to construction errors, ground movement and third-party interactions. While some dents in a pipeline might be dormant features, some have the potential to affect the structural integrity of the pipeline thus resulting in the immediate or delayed failure of the pipeline. It becomes necessary that some measure be put in place for accessing the severity of dents in order to prioritize allocation of the resources in the implementation of management strategies. The codified stipulation of the Canadian pipeline code, CSA Z662-16, proposes the depth based criterion as a measure of the severity of dents in pipelines. History and research have however shown that this approach fails to accommodate other factors such as the localized strain and stress distribution because of the geometry of the dent, 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 approach, the American Society of Mechanical Engineers Standard for gas pipelines, ASME B31.8-16, presents a set of non-mandatory closed form expressions for evaluating the strains in pipelines in a bid to generate the strain state of the dented region based on the dent profile. This technique has, however, been criticized for inaccuracies in its assumptions. Well aware of the pitfalls of existing analytical evaluation techniques for the strains in dented pipeline, some pipeline operators subscribe to the numerical modeling via Finite Element Analysis (FEA) of dents as assessment technique, a procedure regarded to be computationally demanding and resource intensive. The work presented herein is a novel technique for evaluating the strains in dented pipelines based solely on data obtained from inline inspection devices. This study discusses two ideas. The first proposes a new technique for the strain analysis of thin walled structures through a combination of B-Spline interpolation and deformation discretization. This technique allows for the evaluation of all the components of the strain tensor that defines the strain state of the dented pipeline. The second novel approach is extending the proposed technique and the existing ASME B31.8-16 equations into a three-dimensional continuum, thus allowing for a more elaborate analysis without loss in the generality of the procedure.

• Subjects / Keywords

  • Pipelines
  • Dents
  • Strains

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R30Z71970

• 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.