NORTHWEST PIPELINE LLC

Incident Narrative

8:55 PM 6-23-17 A LANDOWNER CALLED NOTIFYING GAS CONTROL THAT THERE WAS A BLOWING GAS SOUND COMPARED TO A JET ENGINE. GAS CONTROL NOTIFIED FIELD OPERATIONS. OPERATIONS RESPONDED WITHIN ONE HOUR AND FOUND RELIEF VALVE BLOWING AS DESIGNED. FIELD OPERATOR SHUT IN BOTH REGULATORS CAUSING RELIEF VALVES TO STOP BLOWING AT 10:15 PM. FIELD OPERATORS DISCOVERED THAT BOTH MOONEY REGULATORS ONSITE HAD TEARS IN THE DIAPHRAGM CAUSING THEM TO FAIL AND LET GAS PRESSURE PAST THEM. FIELD OPERATORS REPLACED THE DIAPHRAGMS AND DOUBLE CHECKED DELIVERY PRESSURE. PRESSURE SHOWED 295 PSI. RELIEF VALVES WERE SET AT 319 AND 321 PSI. NUCLA LATERAL OPERATES AT 300 PSI MAOP. EMPLOYEES VERIFIED DELIVER PRESSURE WAS CURRENT AND ALL VALVES AT STATION WERE LEFT IN NORMAL OPERATING POSITION. LINE PUT BACK IN SERVICE AT 11:20 PM 6-23-17. INITIAL CALCULATIONS OF GAS VOLUMES RELEASED USING TIME GAS CONTROL WAS NOTIFIED AS EVENT START WERE UNDER THE 3,000 MCF REPORTING CRITERIA SO AN NRC NOTIFICATION WAS NOT MADE. ON 6-27-17 IT WAS CONFIRMED WITH THE LANDOWNER THAT GAS WAS BLOWING AT THE LOCATION FROM APPROXIMATELY 10:00 AM 6-23-17 UNTIL THE REGULATORS WERE SHUT IN AT 10:15 PM. WITH THIS ADDITIONAL INFORMATION THE 3,000 MCF REPORTING CRITERIA WAS EXCEEDED BY GAS ESCAPING THE RELIEF VALVE AS DESIGNED. AT 12:32 PM 6-27-17 AN INITIAL NRC NOTIFICATION, # 1182427, WAS MADE, AT 10:02 AM 6-28-17 A FOLLOW UP NRC NOTIFICATION, # 1182511, WAS MADE.