MACKINAW CITY, MI -- What happened to the west leg of Line 5?
Of the 22 anchor supports that Enbridge Inc. is seeking permission to install on the twin 20-inch pipelines crossing underneath the straits of Mackinac, 17 of them are on the west leg.
Of those, five of the proposed anchors are clustered along several hundred feet of the west leg just north of where inspection reports show the pipeline is bent and "ovalized," a term for a section of pipe that's been misshapen enough to lose its roundness.
Documents show that section of pipe is bent in five places and ovalized twice. It's not known for sure how the deformities happened, but Enbridge says they are nothing to worry about, pointing to recent pressure testing as evidence the pipeline is in good shape.
However, inspection reports show that both ovalizations have worsened slightly since 2013.
The anomalies are documented in 2013 and 2016 inspection reports generated by sending "geoppig" robots inside the pipeline to check for problems. The anomalies are also referenced in the 2017 draft analysis of Line 5 released by Dynamic Risk Assessments, which speculates the bends occurred during 1953 construction.
But a retired fluid dynamics expert who has exhaustively studied Line 5 suspects that underwater currents long ago scoured a large section of lake bottom from underneath the pipe, leaving it free-spanning with nothing underneath to support its weight.