Engineer James Mihell of Dynamic Risk Assessment Inc. says there is a 1 in 60 probability that the section of Enbridge Energy Inc.'s Line 5 pipeline running through waters that connect lakes Huron and Michigan will fail between now and 2053.
The state hired the analysts to assess potential energy delivery alternatives in the area.
Environmental activists have accused Dynamic Risk of underestimating the potential of a spill, saying the report "is the oil industry's version of protecting the Great Lakes." Mihell disputed suggestions the firm was low-balling or sugar-coating the risk.
"What we're talking about are very significant consequences," he said.
The report detailed threats that could increase the failure probability of the existing straits section of Line 5, including mechanical damage, weather and incorrect operations. It concluded the passage of time wasn't a major risk itself.
Analysts didn't recommend a specific course of action by the state, but described several alternatives to the pipeline section, including construction of a new tunnel or trench crossing at the same location.
Enbridge consistently has defended the integrity of the pipeline. Officials said the report confirms that Line 5 "could safely operate well into the foreseeable future."
"What is important to note is that the alternatives analysis report found that time has had no bearing on the condition of the pipe," Enbridge spokesman Ryan Duffy said in a statement. "Enbridge's inspection, monitoring and modernization efforts continue to help Line 5 in the Straits operate safely and reliably."
The straits section carries up to 540,000 barrels of light crude oil and natural gas liquids daily.