Assessment of corrosion defects on high-strength steel pipelines

• Main Author: Xu, Luyao
• Other Authors: Cheng, Frank
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Graduate Studies 2013
• Subjects: Mechanical; Pipeline; Corrosion; Finite Element Modelling; Arctic
• Online Access: http://hdl.handle.net/11023/883; https://doi.org/10.11575/PRISM/25027

With the rapidly increasing energy demand, the oil/gas production and pipeline activities have been found in remote regions, such as the Arctic and sub-Arctic regions in North America, which are featured with geological hazards and are prone to large ground movement. The soil induced strain, combined with internal pressure, results in a complex stress/strain condition on pipelines, especially at corrosion defects. It has been demonstrated that the presence of corrosion defect constitutes one of the main threats to pipeline safety. The local stress concentration developed at defect further accelerates the localized corrosion. Moreover, the applied cathodic protection (CP) can be shielded, or at least partially shielded, at corrosion defect. To date, there has been no systematic investigation on the synergism of mechanical and electrochemical factors on localized corrosion reaction at defect. The intrinsic science of this problem has remained unknown, and assessing and predictive models that can be used in practice for pipeline integrity management have been lacking. In this research, various macro- and micro-electrochemical measurements, mechanical testing, and numerical simulation were combined to study the synergism of internal pressure, soil strain and local stress concentration on corrosion at defect on X100 high-strength steel pipelines, and develop theoretical concepts and predictive models to provide guidelines and recommendations to industry for an improved integrity management of pipelines. A mechano-electrochemical (M-E) effect concept, which was built upon the mechanical-electrochemical interaction on metallic corrosion, is proposed to illustrate quantitatively pipeline corrosion under complex stress/strain conditions. Under elastic deformation, the mechanical-electrochemical interaction would not affect pipeline corrosion at a detectable level. However, the plastic formation is able to enhance pipeline corrosion remarkably. Quantitative relationships between the electrochemical potential of steel and ...