NORTHERN NATURAL GAS CO

Incident Narrative

ON MARCH 14, 2016 AT ABOUT 17:00 HOURS LOCAL RESIDENTS AND EMERGENCY RESPONDERS NOTIFIED THE OPERATIONS COMMUNICATION CENTER OF A VISIBLE AND AUDIBLE LEAK IN THE MIDDLE OF A FARM FIELD ABOUT 1.5 MILES SOUTH OF HOWARD LAKE, MINNESOTA. THE LEAK WAS CAUSED BY A CRACK IN THE 3-INCH BRANCH LINE. THE BRANCH LINE CONTAINED OBVIOUS THIRD PARTY DAMAGE. WE BELIEVE THE LANDOWNER WAS DEEP TILLING IN THE LATE 1960'S OR 70'S WHEN HE STRUCK AND BENT THE BRANCH LINE. AFTER NEARLY 50 YEARS, THE DAMAGE FINALLY REACHED CRITICAL FLAW SIZE AND A 1/16-INCH WIDE BY 2-INCH LONG CRACK OPENED. GAS PRESSURE IN THE PIPELINE DROPPED TO AS LOW AS 611 PSI WHERE IT REMAINED. NORTHERN LET THE LEAK CONTINUE UNTIL THE SECTION COULD BE ISOLATED AND BYPASSED USING LINE STOPPING EQUIPMENT. THE SECTION OF PIPE WAS REPLACED AND THE LINE RETURNED TO SERVICE ON MARCH 18, 2016 WITHOUT ANY INTERRUPTION OF SERVICE TO CUSTOMERS. A SECTION OF THE DAMAGED SECTION WAS SENT TO A METALLURGICAL LABORATORY FOR ANALYSIS BUT IT IS HIGHLY UNLIKELY THEY WILL BE ABLE TO DETERMINE WHEN THE DAMAGE OCCURRED.