NORTHERN BORDER PIPELINE COMPANY — Gas transmission and gathering — incident on 2011-07-05

Gas transmission and gathering incident in SACO, PHILLIPS County, MT. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 27090 NATURAL GAS released, $75,000 reported property damage. Operator-reported incident data submitted to PHMSA, generally within 30 days. Records may be supplemented or corrected and do not represent final agency causal findings.

Report number: 20110264.

Operator ID: 13769.

Reported incident date: 7/5/2011 23:00.

Location detail: 0.00

Cause detail: MALFUNCTION OF CONTROL/RELIEF EQUIPMENT

Cause detail: THE 1/4" PILOT VALVE SUPPLY PRESSURE TUBING FAILED, RESULTING IN THE ACTIVATION OF THE MAIN LINE RELIEF VALVE (PSV-5014) AT THE MONCHY FACILITY. TECHNICIAN DISASSEMBLED PILOT VALVE TO INVESTIGATE FOR DAMAGE AND FOUND O-RING FROM THE NOZZLE & SEAT OF PILOT RELIEF VALVE HAD DEGRADATED TO THE POINT OF ALLOWING GAS FLOW IN THE PILOT RELIEF VALVE. THIS RESULTED IN THE PILOT RELIEF VENT LINE TO VENT AT LINE PRESSURE. THE VENTING CAUSED THE VIBRATION ON THE SUPPLY TUBING WHICH IN TURN RUPTURED FROM THIS EXTREME VIBRATION. WHEN THE SUPPLY TUBING FAILED THE 8" RELIEF BECAME UNSEATED AND CAME FULLY OPEN. THIS PILOT RELIEF VALVE IS CALIBRATED & TESTED ANNUALLY AND IS RE-KITTED WITH A PILOT SOFT GOODS KIT ANNUALLY.

PHMSA trend classification: significant incident, not serious.

PHMSA standardized cause: EQUIPMENT FAILURE — MALFUNCTION OF CONTROL/RELIEF EQUIPMENT.

PHMSA indexed costs: $911,600 reported total cost, $626,357.729 in 1984 dollars, $822,057.272 in current-year dollars.

PHMSA trend flags, standardized causes, and indexed costs are analytical fields added to operator-reported incident data. They do not represent final agency causal findings.