GREAT LAKES GAS TRANSMISSION CO

Incident Narrative

ON MARCH 16, 2015, LOCAL TRANSCANADA EMPLOYEES WERE NOTIFIED BY A LOCAL UTILITY EMPLOYEE OF A POSSIBLE GAS LEAK AT GREAT LAKES GAS TRANSMISSION COMPANY'S (GLGT) MAIN LINE VALVE 1-2 LOCATED AT APPROXIMATE MILEPOST 33.40 IN KITTSON COUNTY, MINNESOTA. TRANSCANADA EMPLOYEES FROM THE GLGT ST. VINCENT COMPRESSOR STATION NEAR ST. VINCENT, MINNESOTA, RESPONDED TO THE REPORT AND ARRIVED AT THE MLV SITE AT 1:20 PM CDT. WHEN EMPLOYEES ARRIVED AT THE MLV SITE, THEY OBSERVED THE VALVE SITE TO BE PARTIALLY FLOODED AND GAS BUBBLES TO BE EMANATING FROM NEAR THE BASE OF THE UPSTREAM 20-INCH BLOWDOWN VALVE (1-2-2Y) ON THE 200 LINE PIPELINE. USE OF A GAS DETECTOR REVEALED LOW LEVELS (APPROXIMATELY 10% LEL) OF GAS NEAR THE LEAK SITE. THE UPSTREAM PIPELINE SECTION BETWEEN MLV 1-1-2 TO MLV 1-2-2 WAS THEN SHUT IN AND ISOLATED FROM THE PIPELINE SYSTEM. AFTER PUMPING THE FLOODWATER FROM THE VALVE SITE, IT WAS DETERMINED THAT THE LEAK WAS ORIGINATING FROM A FILLET WELD ON A 2-INCH WELD-O-LET THAT CONNECTED A 2-INCH POWER GAS LINE TO THE 20-INCH BLOWDOWN RISER. THE UPSTREAM PIPELINE SECTION WAS THEN BLOWN DOWN TO ATMOSPHERIC PRESSURE. THIS POWER GAS LINE WAS CONNECTED TO THE RISER AT GROUND LEVEL. BECAUSE THIS CONNECTION WAS SITUATED AT GROUND LEVEL, IT WAS DETERMINED THAT OVER TIME FROST HEAVE PLACED STRESSES ON THE POWER GAS LINE, EVENTUALLY RESULTING IN THE FORMATION OF A CRACK ON THE LOWER SIDE OF THE SUBJECT FILLET WELD AND THE EVENTUAL LEAK. BASED ON THIS INFORMATION, THE POWER GAS CONNECTION TO THE DOWNSTREAM BLOWDOWN RISER WAS ALSO INSPECTED, WHICH REVEALED THE COATING TO BE CRACKED ON THE SIMILAR FILLET WELD AS THE UPSTREAM LOCATION. NONDESTRUCTIVE TESTING OF THIS WELD REVEALED THAT THE WELD WAS NOT CRACKED. NONE-THE-LESS, BASED ON THESE FINDINGS, IT WAS DETERMINED THAT BOTH THE UPSTREAM AND DOWNSTREAM POWER GAS CONNECTIONS WOULD BE REPLACED. AT THIS POINT, THE DOWNSTREAM PIPELINE SECTION BETWEEN MLV 1-2-2 AND MLV 1-3-2 WAS SHUT IN, ISOLATED FROM THE PIPELINE SYSTEM, AND BLOWN DOWN TO ATMOSPHERIC PRESSURE. IN ADDITION TO THE REPLACEMENT OF THE POWER GAS PIPING, SECTIONS OF BOTH THE UPSTREAM AND DOWNSTREAM 20-INCH RISERS WERE REPLACED BECAUSE THE POWER GAS CONNECTIONS WERE RELOCATED TO MORE SUITABLE LOCATIONS ON THE FACILITY PIPING, MITIGATING THE EFFECTS OF ANY FUTURE FROST HEAVE ACTIVITY. REPAIR ACTIVITIES WERE COMPLETED AND THE FACILITIES PLACED BACK INTO SERVICE ON MAY 14, 2015.