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Walter Kresic, vice president of pipeline integrity for Enbridge Energy, discusses the company's biennial inspection of its Line 5 underwater oil pipeline in the Straits of Mackinac. Chad Livengood, The Detroit News

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Mackinaw City — A small two-engine aluminum boat trolled across the Straits of Mackinac Thursday morning towing an orange torpedo-looking watercraft.

When the boat reached the southern pier of the Mackinac Bridge, a worker untied the tow line. Moments later, the autonomous underwater vehicle dove below on a mission to examine a pair of aging five-mile pipelines carrying 540,000 barrels of oil and liquid natural gas each day under the bucolic waterway that divides Michigan’s two peninsulas.

The crew is studying the external integrity of Enbridge Energy’s Line 5, the twin 63-year-old oil pipelines that have come under increased scrutiny because of its age and its location in the fast-moving currents of a body of water connecting Lakes Michigan and Huron. Many Michigan environmental activists have called for the shutdown of the pipelines.

Ballard Marine Construction, a firm based in Washington state, is conducting the weeklong examination of Line 5 for Enbridge using the autonomous underwater vehicle and a remote-operated vehicle to get high-tech sonar scans and video images of the outside of the pipeline.

The sonar and video images will show pipeline operators at Alberta-based Enbridge whether there is any corrosion or obstructions entangled in the pipelines. They also ensure the steel pipes are properly anchored to the floor of Lake Michigan.

Enbridge conducts the external inspection every two years and is required to inspect the internal integrity of the pipelines at least every five years, though the company says the tests of the thickness of the pipe walls are done more frequently.

“We know through many of years of inspecting the pipe how changes occur and how the conditions very specific to the pipe behave. … There’s very little change that happens over two years,” Walter Kresic, vice president of pipeline integrity for Enbridge, said Thursday before joining the Ballard Marine crew for the daylong inspection.

“We’re constantly monitoring the condition of this pipe,” Kresic added.

A high risk

Thursday’s inspection came a day after the U.S. House of Representatives approved a four-year extension of a federal pipeline safety law with a new rule requiring Enbridge to inspect the internal and external integrity of the Line 5 pipelines at least once a year.

U.S. Rep. Candice Miller, R-Harrison Township, specifically drew attention to Enbridge’s Straits of Mackinac pipelines while speaking in favor Wednesday on the House floor of the Protecting Our Infrastructure of Pipelines and Enhancing (PIPES) Act.

“There is zero room for error in the Great Lakes,” Miller said. “There’s a 62-year-old pipeline that is called Line 5 that runs under the Straits of Mackinac, which is right in between Lake Huron and Lake Michigan. Any rupture there would be very, very difficult, if not impossible, to contain.”

The annual inspection requirement applies to pipelines that rest more than 150 feet under water. Line 5 runs to depths of up to 290 feet under water.

Miller helped secure the annual inspection requirement after introducing a separate bill calling for the U.S. Department of Transportation to conduct its own analysis within 18 months that could be used to shut down the pipeline if the federal government deemed it a risk to “life, property or the environment.”

“That got people moving around here a bit,” Miller said in a Thursday telephone interview.

The 645-mile-long Line 5 moves Canadian light crude oil and natural gas liquids used to produce propane and other petroleum products across the Upper Peninsula, under the Straits of Mackinac and south through the Lower Peninsula.

The pipeline then joins up with Enbridge’s Line 6B pipeline in Marysville, where the oil is sent south to refineries in Detroit and Toledo and the natural gas liquids are sent through a pipeline running under the St. Clair River’s bedrock to a propane refinery in Sarnia, Ontario.

The Straits of Mackinac section of Line 5 has come under intensifying scrutiny in recent years from environmentalists and politicians of all political stripes since the company’s Line 6B pipeline ruptured in July 2010 in Calhoun County, polluting the Kalamazoo River with 840,000 gallons of heavy crude — the largest in-land oil spill in U.S. history.

Kresic said Thursday Enbridge has “never had an incident” with Line 5 under the Straits of Mackinac and that there are control valves on both peninsulas to shut off the flow of oil “within a couple of minutes.”

“The lifespan of any engineering infrastructure is really indefinite as long as it’s maintained in a way that keeps it at the level we want it to be,” Kresic said. “What we’re seeing on this line is that it really is as good as new. It can go on operating indefinitely in this way as long as we continue to apply the programs that we’re applying.”

Tracking ‘every inch’

The crew from Ballard Marine began its diagnostics work earlier this week, battling waves up to 5 feet tall on Wednesday.

On Thursday morning, the straits were unusually calm as the crew prepared to launch the $2.1 million state-of-art autonomous underwater vehicle.

The underwater vehicle’s “flight” pattern is pre-programmed to slowly hover over the pipelines, making 16 total passes during multiple trips across the straits this week, said Chris Bauer, operations manager for Ballard Marine.

The two underwater vehicles collect structural data and images of “every inch of the pipeline,” Bauer said.

“When we do that, we’re inspecting all of the anchor supports very, very thoroughly for contact, stabilization, to make sure that they’re not leaning, that there’s no rope or wire wrapped around them,” Bauer said. “... That’s stuff we want to get cleared right away.”

The underwater imagery is melded with global positioning measurements for the pipelines to ensure anchors haven’t shifted in the lake bottom.

Bauer said the underwater images will help Enbridge ensure there’s no more than a 75-foot span between each anchor that supports the pipeline, which was constructed in 1953 using seamless sections of pipe, none of which have ever been replaced.

“From our point of view, that pipe, it’s unbelievable how good of shape that pipe is in,” Bauer said. “It’s in immaculate shape.”

clivengood@detroitnews.com

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