NORTHERN NATURAL GAS CO

Incident Narrative

"AT 14:05 HOURS ON AUGUST 6, 2025, A NORTHERN NATURAL GAS OPERATIONS TECHNICIAN DISCOVERED A RELIEF VALVE VENTING AT THE MINNEAPOLIS, MINNESOTA NO. 1R (STATION NO. 753160) IN CARVER, MINNESOTA. THE OPERATIONS TEAM CONTACTED THE LOCAL FIRE DEPARTMENT AND SHERIFFS DEPARTMENT TO SUPPORT WITH THE CLOSING OF COUNTY ROAD 40. THE ROAD WAS SUCCESSFULLY CLOSED AT 14:24 HOURS UNTIL THE OPERATIONS TEAM WAS ABLE TO DIVERT FLOW THROUGH THE STATION BYPASS AND SUCCESSFULLY STOPPED THE RELIEF VALVE VENTING AT 14:28 HOURS. THE COUNTY ROAD WAS THEN REOPENED AT 14:35 HOURS. DURING THE ONSITE INSPECTION OF THE RELIEF VALVE THE OPERATIONS TEAM, IT WAS BELIEVED THAT THE RELIEF VALVE AND RELIEF PILOT VALVE WERE DAMAGED BY DEBRIS PREVENTING IT FROM RESEATING AND CLOSING. THE DEBRIS WAS SUSPECTED TO HAVE ORIGINATED FROM RECENT NEARBY CONSTRUCTION ON THE PIPELINE. WHEN THE REGULATOR STRAINERS WERE EXAMINED, THEY WERE FOUND TO HAVE BECOME DISLODGED, RELEASING ANY DEBRIS THEY HELD. THE RELIEF VALVE AND RELIEF VALVE PILOT WERE REBUILT ON-SITE AND VERIFIED FOR PROPER OPERATION. AT 17:00 HOURS ON AUGUST 7, 2025, THE STATION WAS PUT BACK INTO NORMAL OPERATIONS. FOLLOWING THE INCIDENT, THE RELIEF VALVE PILOT WAS SENT TO THE VENDOR TO BE EXAMINED BY A MATERIAL SPECIALIST. THE SPECIALIST FOUND THAT THE PILOT DISK HAD WEAKENED CAUSING THE PILOT TO FAIL OPEN DAMAGING THE RELIEF VALVE BOOT DUE TO THE HIGH VELOCITY OF GAS VENTING THROUGH THE RELIEF VALVE. THIS STYLE OF PILOT DISK WAS KNOWN BY SPECIALIST TO WEAKEN OVER TIME, AND IT IS NO LONGER BEING USED BY THE VENDOR. NORTHERN NATURAL GAS IS LOOKING AT REPLACING ALL PILOT DISKS OF THIS STYLE."