Near-neutral pH Stress Corrosion Crack Initiaion under Simulated Coating Disbondment

• Author / Creator

  Eslami, Abdoulmajid

• This research is aimed at understanding near-neutral pH SCC initiation under disbonded coatings of pipeline steels, and the effect of different environmental and operational factors on crack initiation. Understanding near-neutral pH stress corrosion cracking (SCC) could answer many of the primary questions on crack initiation of SCC which have not yet been answered. It could also assist the development of effective mitigative measures dealing with thousands of kilometer of pipelines containing this form of cracking, in addition to preventive action for future pipeline installations.

  Near-neutral pH SCC usually occurs under polyethylene tape (PE tape) coated pipelines, at locations where the coating becomes disbonded and/or damaged. Ground water can then penetrate under the damaged/disbonded coating, become trapped and form a suitable environment for corrosion and cracking. Despite extensive studies on this topic the details of crack initiation mechanisms in addition to the exact role of environmental and operational factors on crack initiation are not thoroughly understood. Most previous laboratory tests have been done in aggressive loading conditions and ignored the effect of coatings and cathodic protections (CP).

  In order to simulate the conditions responsible for crack initiation, a novel testing setup capable of simulating the synergistic effects of coating disbondment, cathodic protection and cyclic loading was implemented. Using this setup and long term laboratory tests near-neutral pH SCC initiation mechanisms and the effect of some environmental and operational factors on crack initiation were investigated. It was found that near-neutral pH SCC initiation does not necessarily occur in near-neutral pH environments as commonly believed. Depending on the level of CP and CO2 in the underground environment, different localized environments with varying pH values from near-neutral to high values above 10 can form under the disbonded coatings. This significantly affected the corrosion and near-neutral pH SCC initiation mechanisms. These investigations brought out new findings about the effect of environment and operations on near-neutral pH SCC initiation.

• Subjects / Keywords

  • Cathodic Protection
  • Pipeline steels
  • Near-neutral pH Stress Corrosion Cracking
  • Pitting Corrosion
  • Coating Disbondment

• Graduation date

  Fall 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3K99N

• 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.