Federal regulators say corrosion tests done as recently as last year found "metal loss anomalies" along the pipeline that sent thousands of gallons of oil rushing into the Kalamazoo River this week.

Just two weeks ago the pipeline's owner notified the government it was considering replacing section of pipe rather than repairing it, regulators say.

Late Wednesday, the Pipeline and Hazardous Materials Safety Administration or PHMSA -- a division of the U.S. Department of Transportation -- sent Enbridge Energy Partners Ltd a corrective action order in the wake of the spill, spelling out the steps that must be taken before the pipeline is reopened.

It also ordered that the secton of failed pipe be given to the National Transportation Safety Board for testing and a 20-year review of any problems along Line 6B of the 1,900-mile Lakehead System be provided.

The rest of the line was also ordered evaluated.

No cause has yet been determined for the spill. On Wednesday, the Free Press found two PHMSA reports from early this year raising concerns about aspects of the Lakehead System -- one about the safety of particularly kind of pre-1970 pipe that was used at the site of a spill in North Dakota and another questioning corrosion monitoring systems along the same line, 6B, where the west Michigan spill occurred.

No mention of either was made in Wednesday's corrective action order, but it did appear the section of pipe where the incident occurred was of a different kind than that which ruptured in North Dakota. As for Line 6B, the order said it had been most recently assessed for corrosion in June 2009 and October 2007.

While the order did not list the results of that testing, it did indicate there were some concerns. It said that on July 15 of this year -- 11 days before the spill -- Enbridge notified PHMSA of "an alternative remediation plan" to correct "metal loss anomalies" found in the testing. The company was considering pipe replacement instead of repair and that it would take some time to complete.

It was not immediately known whether those anomalies were found in the area of the spill or if that was a piece of the pipeline under consideration for replacement.

A message for comment left with Enbridge's media line was not immediately returned.

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