NORTHERN NATURAL GAS CO

Incident Narrative

"ON MARCH 11, 2025, AT 1335 HOURS, A TECHNICIAN ARRIVED ON-SITE AT THE BLOOMING PRAIRIE, MN BRANCH LINE REGULATOR STATION (MNR-0103) FOR REGULAR MAINTENANCE AND FOUND BUBBLES COMING UP FROM BELOW GROUND NEAR PIPELINE FACILITIES. A PLAN WAS DEVELOPED TO REDUCE PRESSURE FOR INVESTIGATION AND EVALUATION OF THE CAUSE OF THE LEAK. THIRD-PARTY CONTRACTORS WERE MOBILIZED TO PREFORM EXCAVATION AND REPAIRS. AFTER EXCAVATION, IT WAS DETERMINED THAT A 1/4-INCH NIPPLE ON THE CBC01 VALVE BODY BLEED RISER HAD CRACKED AND WAS LEAKING. ON MARCH 13, 2025, AT 1240 HOURS, REPAIRS WERE COMPLETED WITH NEW COMPONENTS AND TESTED FOR LEAKS. LEAK CHECKS WERE PERFORMED AT 100PSIG INTERVALS AS PRESSURE WAS RESTORED WITH NO LEAKS IDENTIFIED. FIELD OPERATIONS COMPLETED RETURNING THE MNB73202 PIPELINE BACK TO REGULAR OPERATING CONFIGURATION AND PRESSURE ON MARCH 13, 2025, AT 1813 HOURS. INVESTIGATION CONCLUDED THE BODY BLEED RISER WAS NOT SUFFICIENTLY SUPPORTED AND DUE TO YEARS OF GROUND FREEZE AND THAWS, THE NIPPLE BODY CRACKED CAUSING THE EVENT. THE REPLACEMENT BODY BLEED RISER WAS INSTALLED WITH A RIGID CONNECTION TO PREVENT REOCCURRENCE."