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Enbridge's 64-year-old underwater oil line passes safety test

A portion of a controversial liquids pipeline system traveling underneath the waterway connecting Lake Michigan and Lake Huron is fit for service, according to operator Enbridge Inc., which recently performed a successful pressure test on the line.

The oil and natural gas liquids pipeline system, known as Line 5, has drawn increased scrutiny in recent years because of its age and location. The system includes two parallel 20-inch-diameter pipes, and the recent pressure test confirmed that the western of the two lines is fit for service, Enbridge said in a June 12 email. Pressure tests are intended to verify the maximum safe allowable operating pressure of a pipeline and can reveal leaks on a line.

To do the test, the company pressurized the line to 1,200 pounds per square inch, or psi — significantly more than the 150 psi at which the pipe usually operates. The line was also tested at 1,200 psi when it was built in 1953, according to Enbridge.

The company plans to test the eastern line of the twin pipe system in the coming days.

"The hydrotest is an industry and regulatory accepted way of confirming that our past maintenance and inspection programs were and will continue to be effective in keeping Line 5 operating safely into the future," the company said in an email. "Enbridge is now focused on completing the second portion of our testing on the east Straits segment of Line 5 in the upcoming week. ... We will collaborate with the state to make the final hydrotest results for both East and West segments of Enbridge's Line 5 crossing at the Straits of Mackinac available when the final testing results are completed."

Enbridge did the recent pressure test while under observation by the U.S. Pipeline and Hazardous Materials Safety Administration, U.S. Environmental Protection Agency, state of Michigan and independent third-party contractors who report to the EPA, the company said.

Michigan officials have expressed concern about the Line 5 system in the past, and in 2016 they demanded that the company share more about the system's integrity and what risks it might pose to the environment and economy. The company has posted online the results of a number of its in-line inspections for the pipeline system. For instance, the company noted that it found more than 400 instances of so-called mill anomalies, which are those that arise as part of the manufacturing process. A majority of these were on the west Straits pipe, and the peak depths of mill anomalies on the east and west pipelines were 37% and 41% of the wall thickness, respectively, according to the company.

Enbridge and some of its related companies in July 2016 agreed in a settlement with federal agencies to pay for $177 million in system upgrades, penalties and government costs. Included in that agreement was an expectation that Enbridge would intensify spill-prevention work in Michigan's Straits of Mackinac, where Line 5 operates. The settlement was related to 843,444-gallon release from a Marshall, Mich., oil pipeline in July 2010 and a 269,934-gallon on a Romeoville, Ill., pipe in September 2010.

The past spills have caught the attention of environmental advocates, prompting the National Wildlife Federation in early 2016 to sue the federal pipeline safety regulator for having approved Enbridge's Line 5 facility response plans. Multiple federal lawmakers also questioned PHMSA's permitting for Line 5 back in 2013.