WILLISTON BASIN INTERSTATE PIPELINE CO — Gas transmission and gathering — incident on 2011-10-06

Gas transmission and gathering incident in POWELL, PARK County, WY. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 3800 NATURAL GAS released, $2 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: 20110383.

Operator ID: 22655.

Reported incident date: 10/6/2011 0:46.

Location detail: 0+00

Cause detail: MALFUNCTION OF CONTROL/RELIEF EQUIPMENT

Cause detail: A DOWNSTREAM STATION REGULATOR #6 (R6) WENT CLOSED DUE TO THE WARM NIGHT TEMPERATURES WHICH REQUIRED A MINIMAL AMOUNT OF GAS TO HOLD THE BILLINGS LINE. THE UPSTREAM REGULATOR #5 (R5)WAS LEAKING ENOUGH GAS TO CREATE AN EXCESS PRESSURE BUILD UP ON THE "SHUT-IN" DRY BED DEHY INLET PIPING. RELIEF VALVE #12 (RV12) OPENED AS DESIGNED AT A SCADA REPORTED PRESSURE OF 719 PSIG TO PROTECT THE MAOP (720 PSIG) OF THE DRY BED DEHY PIPING. AFTER THE RELIEF VALVE OPENED RELEASING GAS, A 1/4 INCH PIPE NIPPLE BROKE OFF ON THE RELIEF VALVE PIPING SUPPLYING PILOT GAS TO THE RELIEF VALVE. THE PIPE NIPPLE THAT FAILED SUPPLIED PILOT GAS TO THE RELIEF VALVE WHICH RESULTED IN LOST PILOT PRESSURE AND PREVENTED THE RELIEF VALVE FROM RESEATING. ONCE THE OPERATOR REACHED THE STATION, THE DEHY PRESSURE WAS VERIFIED AND THE VALVE SUPPLYING GAS TO THE RELIEF VALVE AND PILOT VALVE WAS CLOSED. THE DEHY WAS THEN SHUT IN. ACCORDING TO SCADA TRENDING, GAS VENTED FOR 1 HR AND 15 MINUTES. THE ESTIMATED VOLUME RELEASED WAS CALCULATED TO BE APPROXIMATELY 3,800 MCF WHICH EXCEEDS THE REPORTABLE INCIDENT THRESHOLD OF 3,000 MCF. THE OVERPRESSURE CONDITION RESULTED FROM A LEAKING REGULATOR, NOT BY ACTIONS OF THE GAS CONTROLLER OR STATION PERSONNEL. GAS CONTROL DOES NOT HAVE SUPERVISORY CONTROL OF ANY STATION REGULATORS AND THE STATION WAS UNATTENDED AT THE TIME OF THE INCIDENT. THE PIR CALCULATED IN THIS REPORT WAS BASED ON A 3" BLOW DOWN STACK AND 720 PSIG MAOP. APPENDED PART E5F TO TRANSMISSION SYSTEM PER DOT EMAIL REQUEST FROM BLAINE KEENER ON 3/4/13.

PHMSA trend classification: not significant, not serious.

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

PHMSA indexed costs: $13,531 reported total cost, $9,479.615 in 1984 dollars, $11,694.499 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.