COLUMBIA GULF TRANSMISSION, LLC

Incident Narrative

COLUMBIA GULF TRANSMISSION, LLC, A TC ENERGY COMPANY, OPERATES AND MAINTAINS STANTON COMPRESSOR STATION LOCATED IN STANTON, KENTUCKY. ON SATURDAY NOVEMBER 19TH, 2022 A TC ENERGY CLEANING CONTRACTOR HEARD GAS VENTING INTO THE ATMOSPHERE WHILE PERFORMING THEIR DUTIES AT STANTON COMPRESSOR STATION. THE CONTRACTOR IMMEDIATELY CONTACTED COMPRESSOR STATION PERSONNEL; THE STATION PERSONNEL RESPONDED TO THE GAS RELEASE AT STANTON COMPRESSOR STATION AND ADDRESSED THE UNINTENDED RELEASE OF NATURAL GAS THAT WAS VENTING FROM UNIT 108 BLOWDOWN DISCHARGE STACK. THE STATION PERSONNEL INSPECTED AND SECURED THE AREA TO ENSURE THAT IT WAS SAFE; THEN THEN IDENTIFIED VALVES TO ISOLATE THE GAS LINE. THE LINE WAS ISOLATED AT 14:30 EASTERN TIME. ONCE THE LINE WAS ISOLATED THE STATION OPERATING PERSONNEL BEGAN TROUBLESHOOTING THE ISSUE. ALL ALARMS WERE CLEARED AT THE CONTROL PANEL, FUNCTIONAL TESTS WERE COMPLETED WITH NO NEW ERRORS GENERATED TO ENSURE NORMAL OPERATION OF THE STATION. PRELIMINARY INVESTIGATION IDENTIFIED THE PROBABLE CAUSE THAT LED TO THIS UNINTENDED RELEASE AT UNIT 108 WAS DUE TO A LOSS OF POWER TO A PROGRAMMABLE LOGIC CONTROLLER (PLC) AND RELAY FAILURE. THE LOSS OF POWER TO THIS PLC CAUSED THE COMPRESSOR UNIT BLOW DOWN VALVE (AOV 8810) TO REMAIN OPEN. THE VALVE REMAINED OPEN FOR 50 MINUTES RESULTING IN AN ESTIMATED TOTAL GAS LOST OF 5,328.8 MCF. THE PRESSURE OF THE LINE AT THE TIME OF THE INCIDENT WAS 779 LBS. RELAY K340-2B DID NOT UNLATCH FROM ITS N/C STATE AFTER LOSING ITS POWER OR DE-ENERGIZED STATE TO N/O WHICH WOULD HAVE ALLOWED UNIT SUCTION/DISCHARGE VALVES TO BECOME CLOSED OR INTO A FAIL TO CLOSE/SHUT PHASE PER DESIGN. THIS WOULD HAVE PREVENTED GAS FROM VENTING TO ATMOSPHERE VIA UNIT FOUR INCH BLOWN DOWN SILENCER STACK. WITH POWER RESTORED & RELAY REPLACED, THE REMAINING SECTION OF CIRCUIT WAS TESTED TO MAKE SURE PROPER PANEL FEEDBACK, CONTINUITY TEST TO YARD VALVES COMPONENTS WAS VERIFIED AND SUCCESSFUL.