Lessons learned from Enbridge's Kalamazoo River spill
Enbridge is hoping to turn the page today as the company announced it reached a settlement with the US Environmental Protection Agency and the Department of Justice on the 2010 oil spill that occurred in Marshall, Michigan. The rupture of Line 6B spilled 20,000 barrels into the Kalamazoo River and remains one of the largest and costliest inland oil spills in US history.
How it all unfolded
On Saturday July 25, 2010, control room operators in Edmonton began preparing for a 10 hour shutdown of the Line 6B pipeline, a 455 km section of the Lakehead System which crosses the state of Michigan joining Griffith, Indiana, to Sarnia, Ontario. The shutdown started at 5:55 pm ET.
As per normal procedures, the control room operator proceeded to shut the pumps down sequentially in the direction of flow, starting at the Griffith pumphouse, followed by a shutdown of the La Porte pumps. The operator then began to apply backpressure to the system by closing off an isolation valve just upstream of the Stockbridge pumphouse, increasing the line pressure from 50 to 200 psig and redirecting flow to the Stockbridge storage tanks. The Niles and Mendon pump stations were then shutdown.
Unbeknownst to the crew in Edmonton, a rupture occurred within minutes just upstream of the Marshall pumphouse, causing the Marshall pumps to automatically shutdown. Although a flood of alarms came through the control panel, they were dismissed as the "normal" low pressure warnings which occur during shutdowns due to pump cavitation. Cavitation (or loss of suction) occurs during a phenomenon known as column separation, where the pressure in the pipeline drops below the vapour pressure of the liquid, causing the pipe contents to vapourize. The operator cleared the alarms and proceeded to close the isolation valves near the Niles pump station in preparation for the pending shutdown and inspection. Line 6B was down for 10 hours, as per the regularly scheduled maintenance outage.
A foul smell reported but no leak found
Later that evening, the Marshall City Fire Department was dispatched in response to reports of very strong odours detected near the Marshall airport. Both the fire department and Michigan Gas Utilities technicians scanned the area for oil or gas leaks but found nothing. More 911 complaints came through over the next 14 hours, but the dispatcher repeatedly informed the callers that the area had already been surveyed and no leaks had been found.
Although Enbridge had provided training to emergency responders in the Marshall area in February 2010, the firefighters were seemingly unaware of the nearby oil pipeline and did not search along the Line 6B right-of-way. They also did not contact Enbridge.
After the outage, Line 6B restarts
Early Monday morning, Enbridge operators began preparing Line 6B for a restart. The Niles pump station was to remain out of service for inspection. As the pumps were restarted, more low pressure alarms came flooding through the control panel. Once again, the operators dismissed the alarms and attempted to increase the pressure to clear any air pockets and re-establish flow.
As per normal procedures, the operators performed a material balance (measuring flow through the pumps versus flow received into the storage terminals) and discovered a large mismatch. The shift team lead ordered the shutdown of the pipeline. After consultation with the control centre supervisor, the team concluded this was a case of severe cavitation, where the "missing" crude volumes were filling the empty air pockets in the pipeline instead of filling the tanks. At about 7am Monday morning, the operators attempted a second restart of the pipeline.
Once again, numerous alarms came through the control room as the operators attempted to increase the pressure to re-establish flow. The pumps were again shutdown since the pipeline was unable to attain sufficient pressure to pump the crude to the Sarnia terminal.
A phone call to Chicago
A few hours later, the Edmonton team phoned the Chicago regional manager and asked for someone to walk the line. The Chicago manager replied that there had been no reports of oil spills or suspicious odours and this was probably just a case of faulty instrumentation. He suggested another attempt at restarting the pipeline.
About an hour later, a phone call was finally dispatched to the control centre in Edmonton confirming a major spill had occurred in Marshall, Michigan. Isolations valves were immediately closed. Enbridge would spend the next several years cleaning up the spill, remediating the land and repairing the damage to their reputation. The spill site stretched over 60 kms, impacting marshlands, residential areas, farmland and businesses. Enbridge would eventually buy out several homes located near the affected areas.
The root cause
Line 6B was a 30" pipeline constructed out of 1/4" carbon steel coated with a polyethylene tape with an adhesive backing. The US National Transportation Safety Board (NTSB) concluded that the tape had disbonded in the failed section, causing moisture to become trapped between the surface of the pipe and the tape. The moisture caused the pipe to corrode externally, rendering the pipe's cathodic protection circuit useless. The section of pipe that failed was less than 7 feet in in length.
Line 6B was first installed in 1969. Coating technology has advanced considerably since then. The coatings available today follow the pipe’s contours better and are more resistant to disbonding. Some of the newer coatings also allow cathodic protection to reach the pipe. The entire 455 km length of Line 6B has since been fully replaced in 2014.
Internal procedures not followed
Enbridge's internal procedures required all pipeline operations to be stopped after 10 minutes of uncertain operating status. The "10-minute rule" was implemented in 1991 after 40,000 barrels of oil were spilled in Grand Rapids, Minnesota. However, line start-ups and shutdowns often result in low pressure warnings and material balance mismatches, making operating status difficult to assess. The NTSB concluded that the Enbridge crew had become accustomed to ignoring the 10-minute rule when column separation was suspected.
Isolation valves contained the spill, but . . .
About 80% of the spilled volumes (or 16,000 barrels) occurred during the two failed attempts to restart the line. As is the case with most industrial accidents, the most serious incidents tend to occur during system start-ups or shutdowns, when abnormal operating conditions are very difficult to assess.
Diluted bitumen versus "normal" conventional crude
At the time of the rupture, two batches of crude were in the pipeline: the Cold Lake Blend and Western Canadian Select. The Marshall spill has sparked many debates over whether diluted bitumen is more hazardous or corrosive than conventional oil. However, investigations by the NTSB clearly states the mode of failure was external pipe corrosion, not internal.
Turning the page
Enbridge has spent $1.2 billion to date on clean-up, environmental assessments and public awareness campaigns. The company has made numerous changes to its pipeline inspections, emergency response procedures and operating practices in light of the Kalamazoo River spill. Enbridge has committed to memorializing the Marshall spill, resolving to prevent such an event from occuring in the future.