ST. PAUL, Minn. — An official with Enbridge Energy testified Wednesday that the company's aging Line 3 crude oil pipeline across northern Minnesota is increasingly subject to corrosion and cracking, and that its maintenance needs are expected to grow rapidly unless the company is allowed to replace it.

The testimony launched a 12-day, trial-like "evidentiary hearing" before Administrative Law Judge Ann O'Reilly will give officially recognized parties on both sides a chance to question the opposing side's witnesses. All 60 witnesses scheduled to testify —ranging from Enbridge officials to representatives of environmental, tribal, labor and oil industry groups — filed written testimony earlier, so the focus is on cross-examination.

That means Enbridge officials and their consultants will face potentially sharp but also arcane questioning as they try to persuade O'Reilly to recommend the state Public Utilities Commission grant a certificate of need for the project. Such recommendations can carry a lot of weight in Minnesota's regulatory proceedings, but the PUC is an independent body that will make its own decision.

That's scheduled to happen in late April.

Line 3 carries crude oil from Alberta through North Dakota and Minnesota to Enbridge's terminal in Superior, Wisconsin. Enbridge wants to replace 282 miles of the 1960s-era pipeline in Minnesota with a new 337-mile pipeline on a partially different route that would take it through the pristine Mississippi River headwaters region and areas where Native American tribes still hold treaty rights, including prime wild rice lakes. Construction is already underway in Canada and Wisconsin.

Leadoff witness Laura Kennett, supervisor of pipeline asset integrity projects for Calgary, Alberta-based Enbridge, testified that most of the current Line 3 is coated with polyethylene tape, "similar to how tape is wrapped on a hockey stick." But she said the tape is coming loose, leaving the pipeline increasingly vulnerable to corrosion and stress cracking. She also said the welding method used back then also makes it more susceptible to cracking.

Enbridge has projected that it would need to excavate segments of the current pipeline for checks and repairs around 7,000 times in the next 15 years, she said. But a new Line 3 would use state-of-the-art epoxy coating, modern welding methods and thicker, stronger steel, she said.

Among the parties granted formal "intervenor" status is a racially diverse group of 13 people in their teens and 20s, Youth Climate Intervenors. So the cross-examiners Wednesday included 23-year-old Brent Murcia, of Minneapolis. During his brief opportunity he asked Kennett whether the current pipeline would eventually enter a "terminal phase." She replied that it would, but it hasn't yet.

"The Youth Climate Intervenors are here today to highlight the impacts the pipeline will have for young people and future generations due to climate change," Murcia explained during a break. "We're so excited to be heard in this process because young people aren't usually heard in the process."

While an earlier set of public hearings across the state to gather input from the general public turned raucous, opponents Wednesday were content to watch quietly. They included American Indians in T-shirts and jackets recalling last year's protests on the Standing Rock Reservation over the Dakota Access pipeline. They also included activist Winona LaDuke, who carried a feather from an eagle that she said died in the Canadian tar sands, a gift to her from Athabascan Indians.

A different administrative law judge, Eric Lipman, recommended Wednesday that the PUC formally declare that the final environmental impact statement for the project meets the legal requirements. But he also noted that the adequacy of the document — which runs over 2,000 pages plus around 12,000 pages of appendices — was "vigorously disputed."