There has been multiple reported and documented external stress corrosion cracking (SCC) of above-ground carbon steel pipelines within the past 5 years for a number of in-situ oilsands operators. Majority of these failures were on pipeline carbon steel grades API 5L or Z245.1 with specified minimum yield strength (SMYS) 52 ksi or higher, but there were also reports of external SCC on A106 Gr B and A234 WPB steel grades. All the cracks manifested on the bare (uncoated) Outside Diameter (OD) surface of the pipe, and all were associated with wet mineral wool insulation. Common features include operating temperature between 70°C and 160°C, intergranular cracking morphology, and exposed to wet mineral wool insulation with vintage post 2005.
Previously, SCC of carbon steel pipelines has been commonly reported and investigated for buried pipelines. There is limited information in the industry however on SCC of above ground carbon steel pipelines. Extensive field and lab tests were performed to understand the mechanism, in conjunction with technical studies/literature reviews. This paper provides a summary aimed at increasing the awareness of the industry with this new damage mechanism, and improve public safety.
There are hundreds of kilometers of above-ground carbon steel pipelines located in 32 in-situ oilsands facilities operated by 18 producers in Alberta Canada, with a total thermal oilsands capacity (operating) of 1.8 million barrels per day [1]. A typical in-situ oilsands operation is for recovering bitumen located 75 meters or more below the surface, by the injection of steam. See figure 1.
The first in-situ oilsands operations were commissioned in 1985 in Cold Lake, Alberta. Until recently, there were no reported cases of external SCC of above ground carbon steel pipelines. The first documented external intergranular SCC associated with wet mineral wool was in 2015 for an A234 WPB fitting installed in 2009.
