ENABLE GAS TRANSMISSION, LLC

Incident Narrative

AN ESD WAS ACTIVATED AT THE ENABLE GAS TRANSMISSION (EGT) HINTON TURBINE COMPRESSOR STATION. THE STATION ESD ACTIVATED OPENING THE 6"" AND 2"" STATION VENT VALVES. THE STATION MAIN LINE SUCTION BLOCK VALVE TIED TO EGT LINE AD-WEST DID NOT CLOSE. ENABLE GAS CONTROL RECEIVED ALARMS AND IMMEDIATELY NOTIFIED OPERATIONS TO INVESTIGATE THE INCIDENT. THE OPERATIONS TEAM VERIFIED THE STATION ESD VENTS WERE IN THE OPEN POSITION AND CLOSED THE MAIN LINE SUCTION BLOCK VALVE SECURING THE STATION. AS A RESULT, ROUGHLY 23,000 MCF OF NATURAL GAS VENTED TO THE ATMOSPHERE UNINTENTIONALLY. ENABLE CONTACTED THE NRC TO PROVIDE NOTICE OF INCIDENT ON MARCH 14TH (#1300269) AND A 48 HR. FOLLOW UP (#1300352) ON MARCH 15TH. IT WAS LATER DETERMINED THAT A POWER GAS SUPPLY VALVE, WHICH IS ALSO THE SUPPLY GAS FOR THE STATION ESD SYSTEM, WAS IN THE CLOSED POSITION. THE CLOSED POWER GAS SUPPLY VALVE ISOLATED NOT ONLY THE ACTUATOR SUPPLY GAS TO THE STATION MAIN LINE SUCTION VALVE, BUT ALSO ISOLATED THE ESD PILOT SUPPLY GAS. IT IS ASSUMED THAT THERE WAS A SMALL LEAK ON THE POWER SUPPLY/ESD SUPPLY GAS PIPING THAT CAUSED THE ESD PILOT PRESSURE TO FALL BELOW THE ESD PRESSURE SWITCH SETPOINT. WHEN THE PRESSURE SETPOINT OPENS THE ELECTRIC SIDE OF THE ESD SYSTEM WILL TRIGGER AN ESD AND VENT THE REMAINING ESD PILOT PRESSURE CAUSING THE STATION ESD VALVES TO ACTUATE. PRIOR TO THE ESD (3/10/2021), ANNUAL VALVE MAINTENANCE OCCURRED AT THE INACTIVE HINTON TURBINE COMPRESSOR STATION. ALL STATION VALVES WERE OPERATED AND LUBRICATED DURING MAINTENANCE THIS DAY, INCLUDING THE POWER GAS SUPPLY VALVE. ON THIS DAY, THE TECHNICIAN STATED HE FOUND THE POWER GAS SUPPLY VALVE IN THE CLOSED POSITION. ALTHOUGH IT WAS CLOSED, THE TECHNICIAN PERFORMED THE REQUIRED MAINTENANCE AND LEFT THE VALVE IN A CLOSED POSITION. IT CANNOT BE DETERMINED WHEN THE VALVE WAS INADVERTENTLY CLOSED. BASED ON THE FINDINGS, OQ DISQUALIFICATIONS WERE RECOMMENDED ON OQ TASK 007 OPERATE VALVES FOR 2 ENABLE OPERATIONS EMPLOYEES AS NEITHER ONE RECOGNIZED THE SUPPLY GAS VALVE BEING IN THE WRONG POSITION, OR THAT THE POWER SUPPLY GAS LINE WAS LEAKING PRIOR TO THE MAINTENANCE AND VALVE OPERATION.