In its investigation report released today, the Transportation Safety Board of Canada cited a number of causal factors that led to the February 2013 crude oil pipeline leak near Wrigley, Northwest Territories. The report highlights the use of methanol as a drying agent following pneumatic testing and high residual tensile stresses in the vicinity of the girth weld as contributing factors to the internal stress corrosion cracking which caused the leak.
On 8 February 2013, a pipeline crew was performing a planned investigative dig at km post 391 of Enbridge Pipelines Inc.'s Line 21 as part of its integrity management program. During the excavation, odours and crude oil sheen were noticed. Further examination revealed a crack on the pipe surface near a girth weld. Although no freestanding oil was present, approximately 54 m3 of oil-contaminated soil was removed from the site during clean up.
The investigation determined that the pipeline failure was a result of internal stress corrosion through 98% of the pipe wall thickness, and had likely initiated prior to Line 21 being commissioned in 1985. The investigation also determined that the methanol used as a drying agent following the pneumatic test at the time of construction had likely produced an internal pipe environment conducive to the initiation and propagation of stress corrosion cracking. The crack propagated through the remaining 2% of the pipe wall thickness as a result of fatigue caused by normal pipeline operations.
The National Energy Board issued Order AO-002-SO-E102-2011 on 22 March 2013, requiring Enbridge to complete an additional engineering assessment on the Wrigley-Mackenzie segment of Line 21 to evaluate the fitness-for-service of that segment from a leak-dependent perspective; to submit an assessment of currently available leak detection technologies to determine which is most applicable to Line 21; to submit a plan outlining how and when it will implement the selected technology; to conduct a leak detection and soil contamination assessment at any remaining excavation sites that would not be assessed before the spring 2013 break-up; and to continue to consult with potentially affected people about the incidents and remediation to be taken on Line 21. Enbridge has since complied with all conditions of the Order.
Adapted from press release by Joe Green
Read the article online at: https://www.oilfieldtechnology.com/exploration/05122014/wrigley-enbridge-investigation-pipeline-leak-crack-canada-1094/