Effect of CO2 and R-ratio on near-neutral pH stress corrosion cracking initiation under a disbonded coating of pipeline steel

This study investigates the role of CO2 and cyclic stress R-ratio (R = minimum stress/maximum stress) on near-neutral pH SCC initiation mechanism(s) under a disbonded coating of pipeline steel protected by cathodic protection (CP). It was found that depending on CO2 concentration and level of CP, different localized environments with various pH could be formed under the disbonded coating. When cyclic loading was applied, different SCC initiation mechanisms were involved depending on the pH of the localized environments. Reducing the R-ratio had different effects on the initiation mechanisms. (C) 2011 Elsevier Ltd. All rights reserved.