JD Mollard and Associates

This study was undertaken to assess the relationship between sessional fluctuations in electrical ground conductivity and stress corrosion cracking (SCC) in TransCanada’ Pipeline’s Main Line Valve section 31 (MLV 31) located near Brandon, MB.

The study involved acquisition and analysis of seasonal electrical ground conductivity data (collected with Em38 and Em31 instruments) along MLV 31 in November, February, May and August. Analysis suggested that there may be an association between seasonal changes in electrical ground conductivity and seasonal fluctuations in soil moisture at pipe depth. Geological and hydrogeological conditions at the Brookdale SCC failure site, and at other known SCC sites in MLV 31, led to the hypothesis that the development of SCC at these sites was in part influenced by fluctuating water table and soil moisture.

This hypothesis was validated by evaluating the condition of pipeline at several locations and relating it to the site conditions defined by EM survey data. The study showed that, with the exception of the Brookdale site, all known significant SCC sites could be differentiated from non-SCC and insignificant SCC sites by distinctive ranges of EM38dd vertical (1.5 m depth) and EM31-MkII vertical (6 m depth) conductivity values.

Application of these criteria to the entire study area were then used to identify locations where there may be a higher likelihood of finding significant SCC. Based on study results, several suggestions were made for follow-up studies to further improve the understanding of factors affecting SCC susceptibility in MLV31 and models to locate sites with higher SCC susceptibility.

Pipeline location studies                   Electromagnetic ground conductivity meters