NORTHWEST PIPELINE LLC

Incident Narrative

ON DECEMBER 19, 2022 WILLIAMS GAS CONTROL SENT A START COMMAND TO UNIT 1 AT VERNAL COMPRESSOR STATION, LOCATED ON THE NORTHWEST PIPELINE SYSTEM. SHORTLY AFTER THE START COMMAND WAS SENT, GAS CONTROL RECEIVED A VOLTAGE IMBALANCE ALARM. GAS CONTROL FURTHER INVESTIGATED THIS ALARM VIA THE HMI SYSTEM AND NOTICED THAT THE UNIT 1 LOADING VALVE WAS ISSUING A COMMAND DISAGREE ALARM. IT WAS ALSO NOTED AT THIS TIME THAT THE HMI SCHEMATIC SHOWED THE LOADING VALVE WAS OPEN (IT SHOULD'VE BEEN CLOSED). GAS CONTROL CALLED THE LOCAL ON-CALL TECHNICIANS TO HEAD TO THE SITE TO INVESTIGATE. WHEN OPERATIONS PERSONNEL ARRIVED ON SITE THEY WERE ABLE TO CONFIRM THAT THE LOADING VALVE WAS IN FACT OPEN AND VENTING GAS TO THE ATMOSPHERE. IT WAS DISCOVERED THAT THE VALVE WAS FROZEN IN THE OPEN POSITION. THE TECHNICIANS QUICKLY ACTED TO CLOSE THE LOADING VALVE BY WARMING THE VALVE AND MANUALLY MOVING IT TO THE CLOSED POSITION, CAUSING THE VENTING TO STOP. ONCE THE VALVES WERE COMPLETELY THAWED, OPERATIONS AND GAS CONTROL MANUALLY AND REMOTELY OPENED AND CLOSED THE VALVE TO ENSURE THAT PROPER FUNCTION HAD BEEN RESTORED. OVER THE NEXT SEVERAL HOURS, OPERATIONS WORKED WITH TECH SERVICES TO DEVELOP AN ACCURATE ESTIMATE FOR THE QUANTITY OF GAS THAT WAS RELEASED. A FINAL NUMBER OF 3,790 MSCF WAS CALCULATED. SINCE THE INITIAL OCCURRENCE, THE VALVE HAS OPERATED CORRECTLY EACH TIME AN OPEN / CLOSE COMMAND HAS BEEN ISSUED. ADDITIONAL DETAIL ADDED 02/13/23: THE LOADING VALVE IS A 2' VALVE THAT IS USED TO PURGE AND BRING THE COMPRESSOR UP TO PIPELINE PRESSURE BEFORE THE MAIN UNIT VALVES CAN BE OPENED. THIS IS A FAIL CLOSED VALVE THAT USES PNEUMATIC POWER TO OPEN. ICING WAS PRESENT IN THE OPERATOR AND PNEUMATIC VENT, HOLDING THE VALVE IN THE OPEN POSITION. AFTER HEAT WAS APPLIED TO REMOVE THE ICE, THE VALVE WAS ABLE TO BE MOVED AND CYCLED NORMALLY.