TENNESSEE GAS PIPELINE COMPANY

Incident Narrative

TUESDAY, DECEMBER 11 (DETERMINED WEDNESDAY, DECEMBER 12, THROUGH TRENDING): A SOLENOID OPERATED VALVE ACTUATOR IN THE TENNESSEE GAS PIPELINE COMPANY (TGP) STATION 860 BUILDING B FAILED, ALLOWING THE SUPPLY PRESSURE TO OPEN THE LOAD VALVE TO BUILDING B'S COMPRESSOR UNIT 1B (UNIT 1B) UNIT 1B WAS NOT RUNNING AND WAS IN A NORMAL AVAILABLE-DEPRESSURIZE STATE AT THE TIME OF THE ACTUATOR FAILURE, NO ONE HAD BEEN IN BUILDING B ON DECEMBER 11 OR 12 PRIOR TO THE EVENT, THEREFORE THE ACTUATOR FAILURE WAS NOT DISCOVERED UNTIL DECEMBER 12. WEDNESDAY, DECEMBER 12: MORNING OF DECEMBER 12 - TECHNICIAN WAS CALIBRATING PRESSURE TRANSMITTERS IN THE STATION 860 YARD. FOLLOWING COMPANY PROCESS AND PROCEDURES, HE BYPASSED THE PRESSURE TRANSMITTERS PRIOR TO PERFORMING CALIBRATION. THE CONTROL LOGIC FOR THE STATION 860 CONTROLS QUERIED EACH TRANSMITTER FOR PRESSURES. WHEN THE COMPUTER DID NOT RECEIVE PRESSURE INFORMATION FROM THE THREE DISABLED PRESSURE TRANSMITTERS, IT ISSUED A DEFAULT PRESSURE OF 1000PSIG IN ORDER TO INITIATE A STATION SHUTDOWN DUE TO HIGH-PRESSURE CONDITION. 08:29A - STATION 860 SHUT DOWN. ALL UNITS IN BOTH BUILDINGS A AND B SHUTDOWN. 10:09A - LOCAL FIELD OPERATIONS DISCOVERED THE UNIT 1B VENT VALVE OPEN AND RELEASING GAS TO ATMOSPHERE. THE VALVE WAS IMMEDIATELY SHUT IN AND MANAGEMENT WAS NOTIFIED. 10:58A - GAS LOSS CALCULATIONS FINALIZED RESULTING IN AN ESTIMATED 4,529 MCF TOTAL UNINTENTIONAL RELEASE OF GAS. POST EVENT REPAIRS/ACTIONS: THE BUILDING B LOAD VALVE WAS PLACED IN MANUAL MODE, AND THE VENT VALVE WAS PLACED BACK IN OPERATION AND CLOSED. A NEW VALVE ACTUATOR HAS BEEN ORDERED AND REPAIRS ARE SCHEDULED FOR COMPLETION BEFORE THE END OF JANUARY 2019. BUILDING A WAS PLACED BACK IN OPERATION. POST EVENT EVALUATION - GAS RELEASE: WHEN THE UNIT 1B PLC RECEIVES THE SHUTDOWN COMMAND, IT SHUTS THE UNIT DOWN AND OPENS THE 2-INCH VENT VALVE, RELEASING THE GAS FROM UNIT 1B. IN THIS INSTANCE, THERE SHOULD NOT HAVE BEEN ANY GAS TO RELEASE BECAUSE OF THE AVAILABLE-DEPRESSURIZE STATE OF THE UNIT BUT BECAUSE THE ACTUATOR FAILURE CAUSED THE LOAD VALVE TO OPEN, THE LOAD VALVE FED GAS TO THE VENT VALVE. NOTE THAT BUILDING A CONTROL PROGRAMMING VARIES FROM BUILDING B CONTROL PROGRAMMING IN THAT BUILDING A SHUTS DOWN THE UNITS WITHOUT VENTING GAS. POST EVENT EVALUATION - STATION 860 SHUT DOWN: THE EMPLOYEE WAS FOLLOWING ESTABLISHED PROCESS AND PROCEDURE FOR CALIBRATING THE STATION TRANSMITTERS. THE SITE-SPECIFIC PROCEDURES FOR CALIBRATING THE STATION PRESSURE TRANSMITTERS DID NOT ADDRESS CONTROL SYSTEM SETTINGS WHEN BYPASSING THE PRESSURE TRANSMITTERS. THE SITE-SPECIFIC JOB PROCEDURE HAS BEEN UPDATED TO REFLECT THE ADDITIONAL CALIBRATION REQUIREMENTS PRIOR TO ACTUAL TESTING OF PRESSURE TRANSMITTERS. ADDITIONAL NOTES: 48-HOUR UPDATE NRC 1232934 PART A4 ESTIMATED BASED ON 100 MINUTES RELEASE = 4529 MCF. 3000MCF MET IN APPROX. 1 HOUR 21 MIN.