TENNESSEE GAS PIPELINE COMPANY

Incident Narrative

AT APPROXIMATELY 06:00 HOURS, 11/28/2018, A TGP EMPLOYEE ARRIVED AT STATION 71 AND DISCOVERED NATURAL GAS BLOWING FROM THE 2-INCH UNIT VENT VALVE ON COMPRESSOR UNIT 1B. THE EMPLOYEE IMMEDIATELY CONTACTED THE STATION SUPERVISOR FOR EVENT NOTIFICATION. THE STATION SUPERVISOR IMMEDIATELY DISPATCHED ADDITIONAL EMPLOYEES TO ASSIST. THE STATION E&C TECHNICIAN ARRIVED AT STATION 71 AT 6:20 HOURS AND CONFIRMED NATURAL GAS BLOWING FROM THE 2-INCH UNIT VENT VALVE AND DISCOVERED THE UNIT DISCHARGE VALVE WAS OPEN. AT 6:25 HOURS, THE MANUAL LOCKING VALVE BENEATH THE 2-INCH UNIT VENT VALVE WAS CLOSED THEREBY TERMINATING THE NATURAL GAS RELEASE. THE 2-INCH UNIT VENT VALVE WAS ALSO CLOSED. THE UNIT HAD PREVIOUSLY BEEN BLOWN DOWN FROM AN EARLIER EMERGENCY SHUTDOWN (ESD) TEST AND WAS LEFT WITH THE 2-INCH VENT VALVE IN THE NORMAL OPEN POSITION. AS PART OF POST INCIDENT INVESTIGATION, PRESSURE TRENDING INFORMATION WAS ANALYZED AND IT WAS DETERMINED THE DISCHARGE VALVE OPENED AT 3:25 HOURS AND REPORTABLE VOLUME WAS MET AT 04:35 HOURS. INVESTIGATION ALSO IDENTIFIED ICE HAD FORMED IN THE CONTROL SYSTEM OF THE UNIT 1B DISCHARGE VALVE, IMPAIRING ITS OPERATION, ALLOWING THE DISCHARGE VALVE TO OPEN PREMATURELY THEREFORE ALLOWING NATURAL GAS TO VENT THROUGH THE OPEN 2-INCH UNIT VENT VALVE TO ATMOSPHERE. POST EVENT REPAIRS INCLUDED THE CONTROL SYSTEM OF THE UNIT DISCHARGE VALVE WAS BLOWN CLEAN, FREE OF MOISTURE, AND THE CONTROL SYSTEM FILTER WAS REPLACED. PRIOR TO RETURN TO SERVICE, THE 2-INCH UNIT VENT VALVE WAS CONFIRMED RETURNED TO THE OPEN POSITION, ALSO THE MANUAL LOCKING VALVE BENEATH THE 2-INCH UNIT VENT VALVE WAS CONFIRMED RETURNED TO THE OPEN POSITION. THE UNIT SUCTION AND THE UNIT DISCHARGE VALVES WERE CONFIRMED PROPERLY CLOSED. COMPRESSOR UNIT 1B WAS CONFIRMED SAFE AND READY TO RETURN TO SERVICE AS NEEDED ON 11/28/2018. SINCE 11/28/2018, OPERATIONS HAS REVISED THE WINTERIZATION PLAN FOR STATION 71 TO INCLUDE INSPECTION OF VALVE CONTROL SYSTEMS TO DISCOVER CONDENSATE ISSUES AND ELIMINATE THE ISSUES BEFORE FREEZING CONDITIONS BEGIN. PLEASE NOTE THE FOLLOWING REQUESTED INFORMATION: THE ORIGINAL NRC REPORT NUMBER IS 1231460. THE UPDATED INFORMATION NRC REPORT NUMBER IS 1231506. THE REQUIRED PHMSA 48-HOUR NRC REPORT NUMBER IS 1231637.