Line 3 is old, it's corroding, and it's at the end of it's life.

Enbridge representative Laura Kennett has said,

"Line 3 has experienced an accelerated rate of deterioration associated with external corrosion, Stress Corrosion Cracking, and long-seam cracking due to the disbonded coating and fatigue growth of defects in the flash welded long seams. I consider Line 3 to be in the deterioration stage (Stage 3),as external corrosion growth is increasing in an exponential fashion. Therefore, Line 3 is on a path of ever increasing repairs to mitigate operating risk until it is replaced."

Line 3 is in a corridor called the Enbridge Mainline System, with 6 pipelines in total – Lines 1, 2, 3, 4, 67, and 13.   

Many governmental reports and newspaper articles refer to Lines 3 and 4 as a single unit. Together they are responsible for a number of spills and catastrophes including the explosion in Clearbrook in 2007 that killed two workers. 

Line 3 is also responsible for the largest inland oil spill in US history. Many people are familiar with the Kalamazoo River spill (1.1 million gallons), which the media continues to falsely reported as the largest, but Line 3's little known disaster spilled more than 1.7 million gallons of crude oil near Grand Rapids, Minnesota in 1991. Enbridge is now operating Line 3 at the absolute minimum pressure possible.

2 defects that make line 3 particularly susceptible to ruptures:

1. Defective Steel

Long-seam cracking on Line 3 is attributable to defects from the original manufacturing method of the pipe and the impact of higher operating pressures and pressure cycles.  Manufacturing and construction defects can be the initiation point of cracks, which can grow through repeated stress called “fatigue” in steel.

Some of the manufacturing defects on Line 3 are “hook cracks.”  Hook cracks develop when impurities in the steel become trapped in the weld. The photo shows an example of hook cracks in a cross-section of a pipe weld. In this example, we can see one of the hook cracks has led to a crack that reached all the way through the entirety of the pipe wall. 

The majority of this pipe was flash welded, a pipe manufacturing process that has an inherently higher susceptibility to the formation of defects along the long seam of the pipe.  This combination of these defects and internal pipeline pressure developed into long-seam cracking are directly responsible for the historical ruptures of the Line 3 pipeline.

2. Defective Coating

On Line 3 in Minnesota, 84 percent of the coating is Polyethylene (“PE”) tape,  which has been found to "disbond" or peel from the pipe, leading to corrosion of the pipe walls. This PE tape was documented as a cause of the rupture that spilled near Hardisty, Alberta in 2001. It was also documented as a major cause of corrosion on Enbridge’s Line 9 pipeline, during their recent application to the TSB of Canada to reverse the direction of that line. The defective coating on Line 3 has caused:

  • External corrosion on over 50 percent of its pipe sections between welds (referred to as “pipe joints”).  
  • Ten times as many corrosion anomalies per mile (with a depth of more than 20 percent of the pipe wall thickness) than any other Enbridge pipeline in the same corridor.  

  • Stress Corrosion Cracking affecting over 15 percent of the pipe joints, and five times as many SCC anomalies per mile (with a depth of more than 10 percent of the pipe wall thickness) than any other Enbridge pipeline in the same corridor.

Along Line 3, soils have expanded and contracted from seasonal changes in temperature and moisture, and the friction between the pipe and soils with high clay content has stretched the tape coating and caused it to wrinkle.   Pipelines in soils with more clay, such as parts of western Minnesota, exhibit more stretching of the tape coating because those soils are more prone to movement from settling and wetting. The photo below shows an example of the effect of soil stress on Line 3’s tape coating


External corrosion is the oxidation of the steel and loss of metal on the exterior of the pipeline.  External corrosion on Line 3 is primarily attributed to the coating disbonding from the external surface of the pipe.  Disbonded coating creates entry points for water, oxygen, bacteria and acidic compounds in soil to access the surface of the steel and initiate corrosion.