QUESTAR PIPELINE COMPANY — Gas transmission and gathering — incident on 2011-09-28

Gas transmission and gathering incident in INDIANOLA, UTAH County, UT. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 2280 NATURAL GAS released, $0 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: 20110380.

Operator ID: 12874.

Reported incident date: 9/28/2011 9:50.

Cause detail: MALFUNCTION OF CONTROL/RELIEF EQUIPMENT

Cause detail: SUPPLEMENTAL BEING FILED TO CLARIFY THE CAUSE OF THE INCIDENT. DISCHARGE PRESSURES FROM THISTLE CREEK COMPRESSOR STATION WERE OPERATING NEAR THE PRE-SET RELIEF POINT OF THE THERMAL RELIEF VALVE OFF THE DISCHARGE GAS COOLERS. THE RELIEF VALVE BEGAN TO RELIEVE. THE SITUATION WAS IDENTIFIED BY AN OPERATING EMPLOYEE THE NEXT MORNING. THE RELIEF VALVE WAS ISOLATED, MANUALLY RESEATED, AND TESTED TO BE WITHIN 5% OF ITS INTENDED SET-POINT. IT WAS RESET A LITTLE HIGHER, WITHIN DOT LIMITS, AND OPERATING PRESSURES HAVE NOT BEEN NEAR THE SETPOINT SINCE THE INCIDENT OCCURED. INITIALLY, THE ESTIMATED GAS RELEASE WAS 3.79 MMSCF, BUT UPON FINALIZING THE VENTED GAS CALCULATION, IT WAS DETERMINED THAT THE TOTAL VOLUME OF RELEASED GAS WAS 2.28 MMSCF. QUESTAR PIPELINE COMPANY IS FILING THIS REPORT TO FOLLOW-UP WITH THE REPORT MADE TO THE NRC, THOUGH THE FINAL VENTED GAS VOLUME WAS DETERMINED TO BE BELOW THE REPORTING THRESHOLD FOR UNINTENTIONAL RELEASES.

PHMSA trend classification: not significant, not serious.

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

PHMSA indexed costs: $8,900 reported total cost, $6,194.654 in 1984 dollars, $7,804.788 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.