Design and construction



Built to last: exceptional engineering, extraordinary standards.

Line 5 was built to last. In 1953, Enbridge's Line 5 Straits of Mackinac crossing was built to extraordinary standards, using the finest engineering expertise from across the United States. The twin pipelines under the Straits have not experienced any leaks in six decades of operation – a testament to their design, construction, and maintenance regimen. Line 5 was built for an underwater environment, and still exceeds today's standards for pipeline safety.

Tested to withstand up to four times its operating pressure

Bechtel Corporation – one of the most respected firms in the world, with the Hoover Dam among its achievements – managed the engineering, procurement, and construction of the pipeline. The underwater contractor for the Line 5 Straits crossing was Merritt-Chapman & Scott, the same company that built the iconic suspension bridge over the Straits of Mackinac, and the Line 5 crossing uses the same steel as the bridge. 

The design of the Line 5 Straits crossing was coordinated, and underwent peer review, by engineering specialists from Bechtel, the University of Michigan's Department of Naval Architecture and Marine Studies, and Columbia University's Civil Engineering Department.

Key safety features in the design of the twin pipelines included:

  • Specially manufactured steel, formed from a molten “billet” to produce seamless piping;
  • Heavier-walled pipe. At a minimum of 0.812 inches, the Line 5 Straits crossing is the thickest-walled pipe in our entire North America-wide network, and is much thicker than required by the line’s operation or today’s regulatory requirements;
  • An external coating of fiber-reinforced enamel, recognized as one of the most robust pipeline protection materials.

Before it began operation, Line 5 underwent extensive pressure testing with water (hydrostatic testing) multiple times, at more than twice the maximum operating pressure (MOP) of the line and up to four times the typical normal operating pressure of the pipes.

The twin lines also enter the Straits at a depth of 40 to 50 feet, protecting Line 5 from incidents involving anchors or moving ice packs, and were laid in a dredged ditch to a depth of at least 65 feet.