TENNESSEE GAS PIPELINE COMPANY

Incident Narrative

ON SUNDAY FEBRUARY 21ST, AT 13:20 EST THE HEBRON WITHDRAWAL RELIEF VALVE (313C-103) AT TENNESSEE GAS PIPELINE'S (TGP) LITTLE ACRE STORAGE FACILITY ACTUATED. AT THE TIME OF EVENT, THE TGP OPERATOR, WORKING FROM COMPRESSOR STATION 313, RECOGNIZED A FLOW CHANGE AND INITIATED INVESTIGATION. SIMULTANEOUSLY, A NATIONAL FUEL GAS (NFG) OPERATOR, WORKING IN THE AREA OF THE LITTLE ACRE FACILITY, HEARD THE RELEASE AND CONTACTED THE ON-DUTY TGP OPERATOR AT 13:21 EST. THE TGP OPERATOR NOTIFIED OPERATIONS SUPERVISOR AND ON-CALL OPERATIONS SPECIALIST AT 13:25 EST. AFTER CONFIRMING ASSET OWNERSHIP, PERFORMING SAFE APPROACH PROTOCOLS, AND CONFIRMING PRESSURE WAS BELOW ESTABLISHED MAOP, THE TGP OPERATIONS SPECIALIST ISOLATED RELIEF VALVE AT APPROXIMATELY 13:51 EST. LINE PRESSURE AT THE TIME OF EVENT WAS 1161 PSIG AND SET PRESSURE OF RELIEF VALVE WAS 1250 PSIG. AT 17:20 EST, AN INTERNAL EMERGENCY RESPONSE LINE (ERL) CALL COMMENCED AND DURING THAT CALL, TGP PERSONNEL ANNOUNCED THAT IT HAD DETERMINED THE RELEASE VOLUME EXCEEDED 3,000 MSCF. AT 17:34 EST, TGP NOTIFIED THE NRC (REPORT NO. 1298603) OF THE EVENT AND ESTIMATED THE TOTAL GAS LOSS AT GREATER THAN 3,000 MSCF. THE TOTAL UN-INTENTIONAL GAS LOSS WAS LATER DETERMINED TO BE 28,216 MSCF AND REPORTED TO THE NRC (REPORT NO. 1298717) AS A 48-HR UPDATE. IMMEDIATE CAUSE OF THE RELIEF VALVE MALFUNCTION INCLUDED ICE BUILD-UP WITHIN THE POWER GAS TUBING LINE RUNNING FROM THE BODY OF THE RELIEF VALVE TO PILOT CONTROL. THE POWER GAS TUBING LINE BROKE OFF WHERE THE TUBING THREADS INTO THE VALVE BODY DUE TO THE BUILD-UP OF ICE INSIDE THE TUBING AND RELIEF VALVE BODY. FAILURE OF THE RELIEF VALVE PILOT CONTROL LINE, WHICH SUPPLIES PRESSURE TO THE TOP OF THE VALVE, KEEPING IT IN THE CLOSED POSITION, ULTIMATELY REMOVED PRESSURE FROM THE TOP OF THE RELIEF VALVE AND ALLOWED THE RELIEF VALVE SEAT TO LIFT, INITIATING THE RELEASE. THE ICE FORMATION WITHIN THE POWER GAS TUBING AND RELIEF DEVICE RESULTED FROM EXCESS HYDRATE FORMATION DUE TO EXTREMELY COLD AMBIENT TEMPERATURES LEADING UP TO THE EVENT. THE ROOT CAUSE OF THE ICE FORMATION WAS INSUFFICIENT METHANOL DRIPS TO BREAK THE FORMATION OF HYDRATES IN THE SYSTEM. FOLLOWING THE EVENT, THE FREQUENCY OF METHANOL DRIP INSPECTIONS CHANGED FROM WEEKLY TO EVERY OTHER DAY FOR THOSE LOCATIONS WITH A HISTORY OF HYDRATE PRODUCTION DURING COLD AMBIENT TEMPERATURES.