SCC Inspection and Mitigation Program on Suncor OSPL Pipeline: Field Data Trends and Observations

This paper reviews a recent extensive Stress Corrosion Cracking (SCC) inspection and mitigation program on Suncor Energy’s NPS 16 Oilsands Pipeline (OSPL). The primary focus of the paper will be on the findings, trends, and observations obtained from the actual “as found” field data. Suncor’s SCC management philosophy will also be discussed, including in-line inspection, engineering analysis, data collection and defect mitigation. Suncor Energy owns and operates the 426 km NPS 16” (406.4 mm) OSPL system from the Suncor Oilsands site north of Fort McMurray to Edmonton, Alberta, Canada. The pipeline operates as a batched system and transports a range of products from heavy viscous crude oil, light synthetic crude, naptha and diesel to natural gas liquids (NGL). This pipeline experienced a rupture in August of 2004. The cause of failure was determined to be near-neutral pH Stress Corrosion Cracking (SCC). An extensive excavation and inspection program was undertaken following a comprehensive in-line inspection (ILI) program to detect any crack, metal loss and geometry features. A total of 282 crack field and crack-like features as well as 57 notch-like and non-decidable features were excavated and inspected. A number of trends and observations were identified during the inspection and assessment program. Most of the SCC occurred in an area immediately downstream of a newly commissioned pump station. Also, all SCC was detected in thin wall pipe sections and no SCC was identified in heavy wall pipe sections. Most of the SCC occurred in locations with moderate well to rapidly drained glaciofluvial sands and loamy sands. Field observations and findings along with post rupture metallurgical analysis agreed with recent published developments in the mechanism of near-neutral pH SCC. Suncor completed an extensive integrity program in a relatively short period of time (less than a year). All crack-field and crack-like defects as identified by the UltraScan CD tool were mitigated. Suncor plans to continue their integrity program to ensure the continued safety and integrity of their pipeline facilities.