High-pH SCC: Temperature and Potential Dependence for Cracking in Field Environments

The objective of the work described in this paper was to establish the temperature and potential dependence for propagation of high-pH stress corrosion cracking (SCC) in field environments encountered on TransCanada PipeLine’s system in western Canada. Potentiodynamic and potentiostatic polarization techniques were used to identify the electrochemical potential range for performing SCC tests in the simulated field electrolytes. A slow strain rate technique was used for the SCC assessment. A standard 1N Na₂CO₃ – 1N NaHCO₃ solution was included in the test program as a control. The more dilute simulated field electrolyte was a less potent cracking environment than the 1N Na₂CO₃ – 1N NaHCO₃ solution in that the potential range for cracking was narrower and the maximum cracking velocity was lower at a given temperature. The center of the potential range for cracking with the simulated field electrolyte was consistently more negative than with the 1N Na₂CO₃ – 1N NaHCO₃ solution. This may increase the likelihood that the pipe-to-soil potential of a cathodically protected pipeline lies in the cracking range.