TRANSCONTINENTAL GAS PIPE LINE COMPANY

Incident Narrative

OPERATORS AT MARKHAM GAS PROCESSING PLANT 0.6 MILES NORTH OF STATION 24 NOTICED AN INLET PRESSURE DROP. GOING OUTSIDE OF CONTROL ROOM THEY HEARD AND SAW GAS VENTING FROM BLOW DOWN SILENCER AT STATION 24. OPERATOR WENT TO STATION 24, VERIFIED THE EBD VALVE THAT HAD OPENED, AND OPERATED THE GAS-POWERED ACTUATOR TO CLOSE THE VALVE. THE VALVE WAS CLOSED COMPLETELY AND RELEASE STOPPED. THE CAUSE OF THE RELEASE WAS DUE TO A EIM VALVE ACTUATOR THAT MOVED AN EBD VALVE OPEN WITHOUT RECEIVING ANY SIGNAL TO DO SO. WHILE WE KNOW THE ACTUATOR WAS THE CAUSE WE DO NOT YET KNOW WHY THE ACTUATOR OPERATED. WE HAVE COMPLETED A TEMPORARY MOC, ISOLATED THE VALVE, AND REMOVED THE EIM GAS-POWERED ACTUATOR OFF OF THE VALVE. WE ARE STILL TRYING TO ARRANGE FOR A QUALIFIED SHOP TO INSPECT THE ACTUATOR TO DETERMINE THE ISSUE THAT CAUSE IT TO MOVE THE VALVE. WE INTEND TO HAVE A WILLIAMS REPRESENTATIVE PRESENT DURING THE INVESTIGATION TO VERIFY THE FINDINGS. 1/17/2019 - INITIAL GAS LOSS CALCULATIONS WERE ESTIMATED AT 1MMCF ON 10/23. UPON EXPORT OF DATA FROM THE CONTROL SYSTEM AT STATION 24 AND FURTHER ANALYSIS COMPLETED ON 10/26, IT WAS DETERMINED THE RELEASE VOLUME EXCEEDED 3 MMCF. PIPELINE SAFETY NOTIFIED THE NRC UPON RECEIPT OF THE CORRECTED CALCULATION. 6/10/2019 THE INSPECTION REPORT BY THE THIRD PARTY VENDOR- CI ACTUATION- DID NOT REVEAL ANY CAUSE OR ADDITIONAL INFORMATION. WILLIAM'S TECHS HAD PULLED AND INSPECTED THE SPOOL PIECE JUST AFTER THE EVENT. NOTHING WAS FOUND AT THAT TIME THAT WOULD INDICATE A FAILURE. BECAUSE THE SPOOL WAS PREVIOUSLY INSPECTED BY WILLIAMS PERSONNEL CI ACTUATION WAS NOT ABLE OR WILLING TO DETERMINE CAUSE OF FAILURE. NOTE FROM THIRD PARTY VENDOR: ""ON FRIDAY DECEMBER 13TH, 2018 AT WILLIAMS PARTNERS FACILITY IN MARKHAM TEXAS, I DISASSEMBLED CUSTOMERS GAS OPERATED EMERGENCY BLOWDOWN EIM 1/4 TURN ACTUATOR FOR INSPECTION OF ITS COMPONENTS TO DETERMINE THE CAUSE OF ACTUATOR REPORTEDLY TRAVELING OPEN WITHOUT PROCESS CONDITIONS DICTATING THAT IT DO SO. UPON COMPLETING DISASSEMBLY OF THE SUBJECT ACTUATOR, SEVERAL WILLIAMS EMPLOYEES AND MYSELF VISUALLY INSPECTED ALL ACTUATOR COMPONENTS FOR ANY INDICATION OF EXCESSIVELY WORN, DEFECTIVE, OR FAILED PARTS. NONE WERE FOUND. I WAS AT THIS TIME INFORMED BY WILLIAMS EMPLOYEES THAT FOLLOWING ACTUATORS UNDESIRABLE OPERATION, BUT PRIOR TO MY DISASSEMBLY AND INSPECTION, MULTIPLE O-RINGS ON THE ACTUATOR MOUNTED TRAVEL CONTROL VALVE WERE REMOVED AND REPLACED WITH NEW TO PREVENT A RE-OCCURRENCE OF THE ABOVE NOTED UNDESIRED OPERATION. DUE TO FUNCTION CRITICAL PARTS (CONTROL VALVE O-RINGS) BEING REPLACED WITH NEW FOLLOWING THE SUBJECT INCIDENT, BUT PRIOR TO MY INSPECTION, I AM UNABLE TO PROVIDE AN EVIDENCE BACKED CAUSE OF THE AFOREMENTIONED UNDESIRED FUNCTION."" EIM GAS-POWERED ACTUATORS THAT ARE ON THE EBD SYSTEM ARE OBSOLETE AND HARD TO OBTAIN REPAIR PARTS. PARTS ARE EXPECTED BY CI ACTUATION THIS WEEK (WEEK OF 6/10) AND WILL BE INSTALLED IMMEDIATELY ONCE RECEIVED. RETURN TO SERVICE EXPECTED WITHIN THE NEXT TWO WEEKS.