NORTHWEST PIPELINE LLC

Incident Narrative

ON 03/09/2024, AT 2:45 AM, THE CISCO COMPRESSOR STATION SUFFERED A POWER OUTAGE ON THE ESD SYSTEM STRING, TRIGGERING AN UNINTENDED EMERGENCY SHUTDOWN (ESD) RESULTING IN A RELEASE OF 45 MMCF OF NATURAL GAS. WILLIAMS GAS CONTROL RECEIVED AN ALARM INDICATING THE CISCO COMPRESSOR STATION EXPERIENCED A FACILITY ESD EVENT. THE COMPRESSOR STATION WAS PRESSURIZED BUT NOT RUNNING AT THE TIME. PIPELINE CONTROL IMMEDIATELY NOTIFIED OPERATIONS, WHO DECIDED TO WAIT UNTIL DAYLIGHT TO RESPOND. THE DECISION WAS BASED ON PERSONAL SAFETY RISKS FROM NAVIGATING THE TERRAIN, AND THE BELIEF THAT THE STATION WAS STABILIZED DUE TO FAIL-SAFE VENT VALVES AND THE SUCTION AND DISCHARGE ISOLATION VALVES ON THE UPSTREAM AND DOWNSTREAM SIDE OF THE STATION. THE SCADA SYSTEM INDICATED GAS PRESSURE ON THE MAINLINE SEGMENT AT CISCO COMPRESSOR STATION WAS DECLINING AND AT 3:45 AM, THE CONTROLLER CONTACTED OPERATIONS TO FURTHER INVESTIGATE. AN OPERATIONS TECHNICIAN ARRIVED ONSITE ABOUT AN HOUR LATER. THE TECHNICIAN IDENTIFIED THE STATION DISCHARGE VALVE OPEN AND GAS VENTING THROUGH THE 8"" BLOWDOWN. PIPELINE CONTROL REMOTELY CLOSED A MAINLINE BLOCK VALVE TO LIMIT THE RELEASE OF GAS AT 6:10 AM. THE ONSITE TECHNICIAN MANUALLY SHUT IN THE FACILITY TO STOP THE GAS RELEASE AT 6:18 AM. THE OPERATIONS TEAM PERFORMED SIGNIFICANT TESTING AND TROUBLESHOOTING TO IDENTIFY THE CAUSE OF THE ESD AND THE FAILURE OF THE STATION DISCHARGE VALVE. THIS REVEALED A LOOSE CONNECTION ON A POWER JUMPER WIRE THAT SUPPLIES POWER TO THE ESD-RELATED RELAY STRINGS, WHICH GAVE THE INDICATION OF A POWER LOSS AND TRIGGERED THE ESD. ONE OF THE STATION'S DISCHARGE VALVES FAILED TO PROPERLY CLOSE DURING THE ESD DUE TO A SOLENOID MALFUNCTION ON THE DISCHARGE VALVE. AFTER THESE CAUSES WERE IDENTIFIED, FUNCTION TESTS WERE COMPLETED PRIOR TO RETURNING THE COMPRESSOR STATION TO SERVICE.