NORTHWEST PIPELINE LLC

Incident Narrative

ON 9/4/19, WILLIAMS NORTHWEST PIPELINE (NWP) CUSTOMER (AVISTA) GAS CONTROL REPORTED HIGH PRESSURE ALARM TO THE NWP CONTROL ROOM AT 04:04 PT. THE NWP PIPELINE CONTROLLER CONTACTED THE ON-CALL TECHNICIAN AND DISPATCHED HIM TO THE SITE AT 04:14 PT TO INVESTIGATE. THE TECHNICIAN ARRIVED ONSITE AT 04:55 PT TO FIND THE NWP RELIEF VALVE VENTING. THE TECHNICIAN MOVED FLOW FROM PRIMARY RUN TO SECONDARY RUN. THIS LOWERED PRESSURE TO 340 PSIG AND THE RELIEF VALVE RE-SEATED AND STOPPED BLOWING. THE TECHNICIAN ISOLATED, LOCKED OUT AND DEPRESSURIZED THE PRIMARY METER RUN AT 05:10 PT. THE TECHNICIAN DISASSEMBLED THE MOONEY REGULATOR PILOT AND BOOT TO INVESTIGATE. THE TECHNICIAN FOUND A LARGE AMOUNT OF ICE BUILT UP ON PILOT STEM. THE RESULTS OF THE INVESTIGATION WERE: THE REGULATOR PILOT FAILURED DUE TO ICE IN PILOT, CAUSING RISE IN PRESSURE AND THE RELIEF VALVE TO OPERATE. THE ICE IN THE PILOT WAS DETERMINED TO BE CASUED BY DITHIAZINE BUILD UP IN PILOT FILTER AND FILTERS FAILURE TO CONTAIN THE HYDRATES CREATED BY THE THE REACTION OF THE FILTER MEDIA REMOVING THE DITHIAZINE. PROPER REPAIRS WERE MADE ON 9/4/19 INCLUDING: 1) A NEW SULFUR FILTER WAS INSTALLED; AND 2) AN ADDITIONAL DESICANT FILTER IN SERIES AFTER THE SULFUR FILTER TO CAPTURE HYDRATES. NRC REPORTING: AT 08:45, WILLIAMS ENGINEERING PERSONNEL DISCOVERED THE ESTIMATED VOLUME OF GAS RELEASED EXCEEDED THE 3,000 MCF REPORTING THRESHOLD. AS A RESULT, THE WILLIAMS SECURITY OPERATION CENTER NOTIFIED THE NRC AT 09:31 (INCIDENT REPORT # 1257199). A 48-HOUR UPDATE REPORT (INCIDENT REPORT # 1257382) WAS MADE TO THE NRC ON 9/5/19 AT 16:06. AT THE TIME OF THE INCIDENT, THE NWP SCADA MONITORING WAS TEMPORARILY DISABLED DUE TO SCHEDULED MAINTENANCE. PREARRANGED PLANS WERE CONFIRMED BEFORE BEING DISABLED THAT AVISTA WOULD MONITOR AND NOTIFY NWP CONTROL ROOM AS APPROPRIATE. AFTER SCHEDULED MAINTENANCE CONCLUDED, THE NWP SCADA RETURNED TO FULL SERVICE.