Enbridge Line 3 runs 337 miles across Northern Minnesota, passing through the state’s cleanest waters and wetlands; future spills are a major concern.
Pipe corrosion is one source of spills, along with such things as faulty welds or damage from heavy equipment working in the pipeline corridor.
Here’s a quick primer on corrosion.
Pipes are made of steel. It took a lot of energy to turn the ore into high-grade metal. This metal wants to go back to its natural (low energy) state and corrode back to the ore it began as. Pipeline companies have to keep adding energy to prevent corrosion.
Along the pipeline route you will see boxes on electrical poles, called rectifiers. Wires go underground and connect to the pipe and devices called anode beds. The anodes corrode much more quickly than the steel pipe and direct the corrosion there, and away from the pipe.
On the Line 3 project, the pipes have been coated with either a green- or brown-colored epoxy, applied at the factory. This application is never 100 percent perfect. The coating often has microscopic holes, called “holidays.” These spots are susceptible to corrosion and must be patched before the pipe is installed. Construction workers chalk circles on a pipe to indicate holidays that need to be fixed before final installation.
A significant portion of the new Line 3 route is in a brand new pipeline corridor following overhead high-voltage power lines. Electrical interference from these power lines can corrode pipes very quickly. The company has had to install extra equipment to mitigate the electrical interference along this corridor.
For more, here’s how the natural gas industry explains electrical interference.
Above-ground piping will have a different anti-corrosion coating. Sometimes this will be a silver-colored paint. Sometimes the pipe is covered with insulation,which can be another source of corrosion if moisture gets in between the insulation and the pipe.
Piping is above-ground at pump stations. These pumps are needed to keep the viscous tar sands crude moving through the pipe.
Some of this above ground pipe allows the company to inspect inside the pipe, using a device referred to in the trade as a “pig.” It’s an instrument that can be run inside the pipe between pump stations, looking for corrosion. Pipeline operators are required to periodically inspect the pipes on the inside and schedule repairs as needed.
We know some of the pipes being used for Line 3 have sat outside in the elements for years, degrading their protective coatings. Enbridge has done some recoating. Still, it’s a matter of concern.