NORTHERN NATURAL GAS CO

Incident Narrative

ON JULY 1, 2022, AT 0528 HOURS, OGDEN FIELD TEAM, WAS NOTIFIED BY A NEIGHBOR OF BLOWING GAS AT THE OGDEN, IOWA, COMPRESSOR STATION. TECHNICIAN ARRIVED AND OBSERVED GAS BLOWING OUT OF THE VALVE-29 REGULATOR BUILDING. IN ORDER TO ISOLATE THE LEAK AND GAIN ACCESS TO THE BUILDING THE TEAM HAD TO BLOW DOWN APPROXIMATELY 10 MILES OF 20-INCH PIPE ON THE M520B BETWEEN THE OGDEN COMPRESSOR STATION AND VALVE NUMBER TWO, NORTH OF THE STATION. ONCE THE LINE WAS BLOWN DOWN THE TEAM WAS ABLE TO ACCESS THE BUILDING AND FOUND A 1-INCH VALVE AND NIPPLE HAD SEPARATED FROM A 8-INCH BLIND FLANGE JUST ABOVE WHERE THE THREADS ENGAGED THE FLANGE. THE REMAINING PIECE OF NIPPLE WAS EXTRACTED FROM THE FLANGE AND A 1-INCH BULL PLUG WAS INSTALLED. THE M520B WAS RETURNED TO SERVICE ON JULY 1, 2022, AT 1630 HOURS. AT 13:26, PRELIMINARY GAS LOSS CALCULATIONS WERE COMPLETED. THE CALCULATION SHOWED THE REPORTING THRESHOLD WAS MET AT 11:05. WITH THAT CONFIRMATION, THE NRC WAS NOTIFIED AT 13:49. A TRAINING SESSION FOR PIPELINE CONTROL VALVE/REGULATOR VIBRATION RISK AWARENESS COMPLETED IN SEPTEMBER, 2022. THIS INCLUDED A TECHNICAL BULLETIN REVIEW AND DISCUSSION OF KNOWN ASSOCIATED CURRENT AND PRIOR ISSUES TO INCREASE AWARENESS AND RECOGNITION AND REMEDIATION.