ENBRIDGE ENERGY, LIMITED PARTNERSHIP

Incident Narrative

ON FEBRUARY 15 AT APPROXIMATELY 14:15 LOCAL TIME, WHILE HYDRO VACUUMING TO INVESTIGATE AN INTEGRITY DIG SITE ON LINE 5 AT MP 1606, THE CONTRACT INSPECTOR NOTICED A HEAVY CRUDE OIL ODOR AND CONTACTED ENBRIDGE PERSONNEL. THE LINE WAS IMMEDIATELY SHUT DOWN, AND PIPELINE MAINTENANCE PERSONNEL WERE DISPATCHED TO THE SITE TO INVESTIGATE. FURTHER EXCAVATION AND INVESTIGATION CONFIRMED CONTAMINATED SOIL AND THE PRESENCE OF A SMALL WEEPING DEFECT ON THE PIPE BODY. A PLIDCO SLEEVE WAS INSTALLED AND THE LINE RESTARTED ON FEBRUARY 17 UNDER A TEMPORARY OPERATING PRESSURE RESTRICTION. THE CAUSE OF THE LEAK IS STILL UNDER INVESTIGATION AND A SUPPLEMENTAL REPORT WILL BE FILED ONCE THE INVESTIGATION IS COMPLETE. MONITORING WELLS HAVE BEEN INSTALLED AND A LONG TERM IMPACT ASSESSMENT WILL BE COMPLETED. ENBRIDGE SELF-IMPOSED TEMPORARY OPERATING PRESSURE RESTRICTIONS TO ALLOW COMPLETION OF ADDITIONAL ILI ANALYSIS AND REVIEW OF THE CORRESPONDING DIG/FEATURE INVESTIGATIONS TO IDENTIFY WHETHER THERE WERE ILI FEATURES EXHIBITING SIMILAR CHARACTERISTICS ON LINE 5, AND IF SO, EXCAVATE AND EXAMINE THOSE FEATURES. ENBRIDGE COMPLETED THE FIELD EXAMINATION AND INTEGRITY ASSESSMENTS ON FOUR FEATURES WHICH EXHIBITED ILI SIGNATURES SIMILAR TO THE 1606 FEATURE. BASED ON THE FURTHER INVESTIGATION, ENBRIDGE CONFIRMED THESE INDICATIONS DID NOT POSE A THREAT TO THE INTEGRITY OF LINE 5, AND THE TEMPORARY SELF-IMPOSED OPERATING PRESSURE RESTRICTIONS WERE REMOVED MARCH 7, 2012. PLANS ARE IN PLACE FOR REMOVAL AND ANALYSIS OF THE REPAIRED LEAKING FEATURE LATER THIS YEAR. APPROXIMATELY 400 TONS OF CONTAMINATED SOIL WAS REMOVED FROM RELEASE SITE. UPDATE 10-10-13 THE RESULTS OF THE METALLURGICAL ANALYSIS INDICATE THAT THE METALLURGICAL CAUSE OF THE LEAK WAS A CRACK THAT INITIATED FROM A STRESS CONCENTRATION AT A WELD REPAIR, PROPAGATED BY DUCTILE TEARING THROUGH 80% OF THE WALL THICKNESS, AND ULTIMATELY FAILED BY FATIGUE. THE DUCTILE TEAR WAS MOST LIKELY INDUCED DURING THE COLD EXPANSION OF THE PIPE JOINT DURING MANUFACTURE OR DURING THE INITIAL HYDROTEST OF THE LINE FOLLOWING CONSTRUCTION IN 1953. THE TEAR PROVIDED AN INITIATION SITE FOR FATIGUE CRACK GROWTH THAT PROPAGATED THROUGH THE PIPE WALL DURING SERVICE, RESULTING IN A LEAK OF THE PIPE SECTION.