TENNESSEE GAS PIPELINE COMPANY

Incident Narrative

AT 10:23 AM CST ON 12/28/2021 RELIEF VALVES 96-1A AND 96-2A ACTIVATED IN THE STATION YARD OF STATION 96 IN CAMPBELLSVILLE, KENTUCKY VENTING NATURAL GAS TO THE ATMOSPHERE. THESE VALVES ARE LOCATED 34-FEET APART ON COMMON DISCHARGE PIPING AND ARE 8-INCH MERCER BRAND VALVES. COMPANY PERSONNEL ON SITE VERIFIED THAT STATION DISCHARGE PRESSURE DID NOT EXCEED MAOP AND REDUCED HORSEPOWER IN AN EFFORT TO REDUCE PRESSURE AND ALLOW THE VALVES TO RESET. WHEN THE RELIEF VALVES DID NOT RESET THE MANUAL VALVES, LOCATED BELOW THE RELIEF VALVES, WERE CLOSED AT 10:29 AM CST. THE INTERNAL EMERGENCY RESPONSE LINE (ERL) CALL NOTIFICATION WAS INITIATED PER COMPANY PROCEDURES TO DISCUSS THE INCIDENT. IT WAS DETERMINED ON THE CALL THAT THE QUANTITY OF GAS RELEASED WOULD MEET THE PHMSA-REPORTABLE THRESHOLD AND THE NRC AND PHMSA ACCIDENT INVESTIGATION DIVISION WERE BOTH NOTIFIED. THE INVESTIGATION INTO THE INCIDENT BEGAN THE SAME DAY AS THE EVENT. STATION PERSONNEL ALONG WITH THE RELIEF VALVE VENDOR, TESTED THE VALVE SETPOINTS. THE NORMAL SET-POINT FOR THESE VALVES IS 772 PSIG AND BOTH VALVES WERE SERVICED ON 9/21/2021 BY OPERATOR QUALIFIED PERSONNEL, WHO LEFT THE VALVES AT 772 PSIG. BENCH TESTING THE VALVES SHOWED THAT VALVE 96-1A RELIEVED AT 743 PSIG AND VALVE 96-2A RELIEVED AT 738 PSIG. THE RELIEF VALVES WERE CALIBRATED TO 772PSIG, PLACED BACK INTO SERVICE, AND THE HORSEPOWER RETURNED TO NORMAL OPERATIONS. THE MERCER VALVE REPRESENTATIVES PROVIDED MERCER VALVE CO., INC. TECHNICAL BULLETIN ETB00013, PUBLISHED ON JULY 31, 2015 AFTER THE INSTALLATION DATE OF VALVES 96-1A AND 96-2A, INDICATING THAT EXCESSIVE VIBRATION ON THE RELIEF VALVES PILOTS CAN LEAD TO A REDUCTION DRIFT OF THE SET-POINT PRESSURE REQUIRED TO ACTIVATE THE RELIEF VALVE. THEY INDICATED THAT THE VALVES ARE ALSO SUSCEPTIBLE TO PULSATION IN THE PILOT SENSING LINES WHEN LOCATED CLOSE TO COMPRESSION. IT IS BELIEVED THAT THE DRIFTING SET POINT AND PILOT SENSING LINE PULSATION LED TO THE ACTIVATION OF THESE VALVES AT A LOWER PRESSURE THAN THE NORMAL SETPOINT. ON JANUARY 12, 2022, BASED ON THE INPUT FROM THE VALVE REPRESENTATIVES, THE PILOTS ON THE RELIEF VALVES WERE REPLACED AND DAMPENERS WERE INSTALLED TO ENSURE PULSATION DOES NOT PLAY A FACTOR IN THE FUTURE. ADDITIONAL REMEDIAL ACTIONS WILL BE EVALUATED TO ADDRESS THE SET-POINT DRIFT. UNTIL ADDITIONAL REMEDIAL ACTIONS ARE ASSESSED, THE TESTING FREQUENCY FOR THESE VALVES WILL BE INCREASED FROM ANNUALLY TO MONTHLY.