TENNESSEE GAS PIPELINE COMPANY

Incident Narrative

IN THE TGP STATION 823 A-1 COMPRESSOR BUILDING, A GAS DETECTOR UNIT PROVIDE ALARM AT 20% LFL. THE ON DUTY OPERATOR SAFELY ENTERED THE BULDING TO STOP UNIT #4A BUT THE GAS DETECTOR UNIT SENSED 40% LFL AND INITIATED A COMPLETE STATION ESD. THE UNIT #4A, #2 CYLINDER HEAD END UNLOADER VALVE STEM HAD A PACKING LEAK OF APPROXIMATELY 5 MCF. DURING THE STATION ESD PROCESS WHICH STOPPED THE UNIT, THE PIPING SYSTEM DID NOT FULLY ISOLATE AS VALVE 823-AD1 DID NOT COMPLETELY CLOSE. OPERATION STAFF DETERMINED IT WAS SAFE TO CLOSE VALVE 823-AD1 THEREFORE TERMINATING THE RELEASE OF NATURAL GAS TO ATMOSPHERE. NOTIFICATIONS WERE MADE TO THE NRC AND TO THE LOUISIANA STATE POLICE AS REQUIRED. INVESTIGATION FOUND THE CYLINDER HEAD END UNLOADER POCKET PISTON SET SCREW HAD BACKED OUT ALLOWING A NUT TO LOOSEN; PULSATION CAUSED THE POCKET PISTON TO DISENGAGE; THE MISSING PISTON ALLOWED THE VALVE STEM TO OVER TRAVEL ALLOWING GAS TO VENT AROUND THE GLAND AND OUT TO ATMOSHPERE THROUGH AN UNLOADER WEEP HOLE. VALVE 823-AD1, SLIGHTLY OFF CLOSE LIMITS, ALLOWED ADDITIONAL VENTING OF NATURAL GAS BEFORE OPERATION STAFF SAFELY CLOSED THE VALVE. THE VALVE SET LIMITS HAVE BEEN RESET AND THE VALVE ASSEMBLY INPSECTED. THE HEAD END UNLOADER HAS BEEN REPAIRED. INSPECTION OF OTHER HEAD END UNLOADER COMPONENTS FOUND TWO OTHER UNITS WITH LOOSE SET SCREWS; THESE UNITS HAVE ALSO BEEN REPAIRED.