Energy giant Enbridge Inc. has commenced work on a $6.5-billion project that will replace over 1,000 miles of its Line 3, a crude oil pipeline the company says is at risk for corrosion due to failures in its protective coating.The first segment to be built in the Canadian section of the project will comprise about a quarter of the total length, starting at the line’s origin in Hardisty, AB. The pipeline carries crude from the Alberta oilsands to Wisconsin, via Saskatchewan, Manitoba, a small section of North Dakota and Minnesota. In replacing the original Line 3, which went into service in 1968, Enbridge will also be increasing the pipeline’s capacity; the original 34-in. line will be replaced with a new 36-in. line that’s expected to nearly double the volume of oil transported daily. Line 3 was originally built to transport 760,000 barrels per day of light, medium and heavy crudes. In 2010, Enbridge voluntarily limited the line to 390,000 barrels per day of light crude only. The new pipeline is expected to initially transport 760,000 barrels per day again. Its full design capacity will be 844,000 barrels per day. Line 3, unlike a number of the company’s other pipelines, was protected with a tapecoat, which has disbonded from the pipeline steel. Enbridge says the coating failure has sped corrosion rates, causing concerns over deterioration in the line. The company plans to construct the new pipeline of high-strength GX-70 steel, with a nominal wall thickness of 0.515 in. (with stretches made of thicker pipeline when necessary, such as segments installed via road bore or horizontal directional drilling). The mainline will be coated with 14 mils of epoxy bonding, and stretches installed via trenchless methods will be coated with 50 mils.