NORTHERN NATURAL GAS CO

Incident Narrative

AT 1405 ON SUNDAY, OCTOBER 27, 2013 NORTHERN NATURAL GAS COMPANY'S OPERATION COMMUNICATION CENTER (24 HOUR EMERGENCY) RECEIVED A PHONE CALL FROM A NEIGHBOR STATING THAT THERE WAS A VERY LOUD NOISE COMING FROM THE INTERCONNECT WITH NORTHERN BORDER PIPELINE. LOCAL EMPLOYEES WERE NOTIFIED AND RESPONDED WITHIN 30 MINUTES. THE INTERCONNECT IS ABOUT 1.5 MILES EAST OF WELCOME, MN WHERE EMPLOYEES LIVE. THE LOCAL EMPLOYEES IMMEDIATELY INVESTIGATED THE CAUSE. THE RELIEF IS SET TO RELIEVE AT 830 PSI BUT WAS OPEN AND RELEASING NATURAL GAS TO THE ATMOSPHERE AT 770 PSI. THE RELIEF VALVE RESET AUTOMATICALLY WHEN THE PRESSURE DROPPED TO 740 PSI AFTER NORTHERN BORDER SHUT OFF ITS DELIVERY. THE METER AND REGULATING STATION NORMALLY OPERATES BETWEEN 770 AND 780 PSI. CHANGES TO DELIVERY VOLUMES OCCUR OFTEN. THE GAS CONTROL LOG DID NOT INDICATE A DROP IN PRESSURE FOR THE 30 MINUTES THE RELIEF VALVE WAS OPEN. THE LOCAL EMPLOYEES DISASSEMBLED THE PILOT AND FOUND DIRT AND MOISTURE INSIDE THAT MUST HAVE CAUSED THE RELIEF VALVE TO OPEN AT THE LOWER PRESSURE. THE PILOT WAS REPAIRED, REINSTALLED AND TESTED. THE EMPLOYEES LEFT AFTER THEY VERIFIED THAT EVERYTHING WAS BACK TO NORMAL, AROUND 1800 HOURS. THE ATTACHED PRESSURE LOG SHOWS THAT NORTHERN NATURAL GAS CONTROLLERS CALLED NORTHERN BORDER GAS CONTROLLERS TO CEASE DELIVERIES UNTIL NORTHERN NATURAL EMPLOYEES COULD APPROACH THE RELIEF VALVE AND AFFECT REPAIRS. NORTHERN BORDER RETURNED TO NORMAL OPERATION AFTER THE PILOT WAS REPAIRED AND TESTED. LOCAL EMPLOYEES NOTIFIED NORTHERN NATURAL GAS CONTROL WHO NOTIFIED NORTHERN BORDER GAS CONTROL.