Protecting what matters
The Line 5 Straits of Mackinac crossing: How we safeguard the Great Lakes
The Straits of Mackinac, where Lake Huron and Lake Michigan meet, support recreation, commerce and a Michigan way of life.
The Straits are a natural treasure—a place worth protecting. That's why we take special precautions with our dual Line 5 pipelines—which travel a distance of 4.5 miles along the bottom of the Straits—to protect this resource.
Keeping a watchful eye
We monitor Line 5 around the clock, using specially trained staff and sophisticated computer modelling systems.
All system alarms generated by our automated leak detection equipment, and relayed to our control center staff, are assumed to be leaks until they are conclusively proven otherwise.
Enbridge personnel also perform aerial line patrols at the Straits every two to three weeks.
No Anchor Zone
The Line 5 Straits of Mackinac crossing is in a No Anchor Zone, and identified as such in National Oceanic and Atmospheric Administration (NOAA) navigation charts. The zone is identified as such with lighted signs near both shores.
There are also several high-voltage lines that cross the Straits in the vicinity, and the water current at the Straits is relatively fast--which also discourages ships from anchoring in the area.
More importantly, the heavy pipe wall thickness, high ductility, low diameter-to-wall-thickness ratio, and low operating stresses of the Line 5 Straits crossing all provide a substantial margin of safety against any anchor strike threat.
A low-pressure environment
Line 5 is tested and permitted to run at 600 pounds per square inch (PSI), but actually operates at 150 PSI—or 25% of the maximum operational pressure (MOP)—to reduce strain on the system.
To put that in context, a garden hose pushes water through at 40 to 80 PSI.
A closer look
We make regular visual inspections of the twin pipelines’ exterior, using expert divers and remotely operated submersibles, for a thorough look at the twin 20-inch-diameter lines and their immediate environment along the bottom of the Straits.
We use the information that we collect to strengthen underwater supports for the lines.
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Examining the pipe, inch by inch
In-line inspection tools regularly travel through Line 5, providing a level of detail similar to MRIs in the medical industry. These high-tech tools, operated by companies such as Baker Hughes, a GE company, allow us to examine the interior walls of our pipes inch by inch, and alert us to features that may require a closer look.
These third parties conduct the inspection and provide us data on the pipe’s condition. We then submit their findings to the federal regulator.
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A sturdy support network
Through our Line 5 span management program, we monitor the length of unsupported pipeline spans, and make necessary repairs to prevent the movement of the pipes along the lakebed.
Support anchors, consisting of 10-foot steel screws, are augered into the lake bed, and support a steel saddle that secures the twin lines in place.
Since GPS data was first collected more than a decade ago, there has been no measurable movement of the pipes under the Straits.
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Safety in the Straits
This is a special place. And that’s why we take special precautions to continue the safe and reliable operation of Line 5, and protect the Straits of Mackinac.
Automatic isolation valves
We have isolation valves, located on either side of the Straits, that close automatically upon detection of a sudden change in pressure, with full closure occurring within three minutes.
These valve sites are equipped with backup power systems and check valves that will provide automatic protection in the event of a main power interruption.
Intelligent Valve Placement
Isolation valves, which control or stop the flow of crude oil, are a key piece of pipeline safety equipment.
Enbridge has isolation valves at regular intervals along Line 5 through Michigan, and across our North American pipeline system. We monitor our system 24/7/365, and we can remotely close a valve immediately on detection of a potential problem—with full closure within three minutes of activation.
Deep cover
The twin pipes enter the Straits of Mackinac at a depth of 40 to 50 feet, protecting Line 5 from incidents involving anchors or moving ice packs. The pipes are laid in a dredged ditch to a depth of 65 feet.
At depths of more than 65 feet, the pipes are secured to the lakebed with heavy-duty steel screw anchors.
An engineering marvel
The Line 5 Straits crossing was considered an engineering marvel in its day, and still exceeds today’s standards for pipeline safety.
Bechtel Corporation, which built the Hoover Dam, and Merritt-Chapman & Scott, which built the Straits of Mackinac suspension bridge, were intricately involved in the Line 5 Straits crossing’s construction.
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An impermeable coating
The fiber-reinforced enamel coating used along the Line 5 Straits crossing is widely recognized as one of the most robust pipeline protection materials in the world.
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Built to last
Line 5 is built from specially manufactured steel, formed from a molten “billet” to produce seamless piping.
The Line 5 Straits crossing also features heavier-walled pipe. At a minimum of 0.812 inches, it is much thicker than required by the line’s operation or today’s regulatory requirements.
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