Effect of Mechanical Loading Conditions on Near-neutral pH Stress Corrosion Cracking (NNpHSCC) Initiation and Early-stage Growth for Bent Pipeline

• Author / Creator

  Vo, Giao NH

• Near-neutral pH Stress Corrosion Cracking (NNpHSCC) continues causing failures of steel pipelines despite the use of preventative measures such as protective coating and cathodic protection. In pipelines with bends, the issue is more profound as stress is concentrated around the bends and the protective coating layer is more prone to failure there. In this study, axial loads of 50%, 25% and 15% of Specified Minimum Yield Strength (SMYS) were applied to pipe sections bent to 20- and 40-degree angles under a near-neutral pH condition. Pit and crack distribution, as well as pit and crack depth were analyzed. Smaller maximum stresses are found to have a more profound effect on pit and crack initiation at the center of bend. While smaller bending angles experienced less compressive stress and hence pitting initiates more readily on the surface, larger bending angles suggested a more drastic change in residual stress, resulting in more pits and cracks growth. The crack distribution between the two changes near the center of bend, but no difference was found along the length of the pipe. The study also suggested that despite having a compressive residual stress near the center of bend, pits and cracks can still be initiated from the breakage of mill scale exposing the surface of the pipe, and cyclic loading changes the stress distribution along the pipe length and depth, which aids in pit and crack initiation.

• Subjects / Keywords

  • Circumferential Near-neutral Stress Corrosion Cracking
  • Axial Bending
  • Crack Initiation and Stage I Growth
  • Residual Stress Distribution

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-fhpg-j242

• 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.