The Transportation Safety Board of Canada (TSB) recently released its investigation report (P22H0023) into a pipeline rupture that resulted in an explosion and fire near Fox Creek, Alberta.
On the morning of April 7, 2022, a natural gas pipeline operated by NOVA Gas Transmission Ltd. ruptured. The escaping gas ignited and resulted in a fire that burned a 12,000-m2 area. The fire self-extinguished after the flow of gas was stopped by manually closing isolating valves upstream and downstream of the rupture.
There were no injuries, and no evacuation was required.
TSB’s investigation found that the pipeline ruptured due to reduced pipe wall strength caused by external corrosion. The pipeline’s external coating system had degraded over time, exposing the surface of the pipe to the external soil environment.
An impressed current cathodic protection (CP) system had been installed to protect the pipe surface from corrosion in the event of degradation or failure of the external coating. But in this occurrence, the CP system was not adequately protecting the exposed surface of the pipe as intended.
The pipeline’s proximity to a nearby third-party pipeline—combined with a degraded pipe coating, low soil resistivity, and an incomplete electrical CP bond—contributed to stray current interference, according to the TSB. This led to accelerated external corrosion of the pipeline at the occurrence location.
Currently, there is no centralized system in Canada for consolidating information about pipeline CP system locations and operating characteristics. If pipeline operators are not fully aware of the operating characteristics of third-party CP infrastructure located in close proximity to their pipelines, CP effectiveness may be compromised, according to the TSB. In turn, this increases the risk of corrosion.
After the occurrence, NOVA Gas Transmission Ltd. replaced the damaged sections of pipe and initiated steps to permanently shut down the entire pipeline.
For more information, visit www.tsb.gc.ca/eng.