NORTHERN NATURAL GAS CO — Gas transmission and gathering — incident on 2015-04-04

Gas transmission and gathering incident in Not Within a Municipality, DELEWARE County, IA. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 3448 NATURAL GAS released, $1,200 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: 20150051.

Operator ID: 13750.

Reported incident date: 4/4/2015 19:27.

Location detail: 54.51

Cause detail: OTHER EQUIPMENT FAILURE

Cause detail: A NEAR-BY RESIDENT REPORTED A NOISE AT THE EARLVILLE, IOWA, COMPRESSOR STATION AT 19:30 HOURS ON 4/4/15. OPERATIONS RESPONDED AND AND FOUND THE FISHER 399 FUEL RUN RELIEF VALVE VENTING. OPERATIONS ISOLATED THE FUEL RUN TO STOP THE VENTING GAS. INVESTIGATION FOUND THE FISHER 6356EBH RELIEF VALVE PILOT WAS NOT HOLDING THE SET POINT AND OPERATING PREMATURELY. OPERATIONS REPLACED THE FISHER 6358EBH-5 PILOT WITH A NEW ASSEMBLY. THE NEW ASSEMBLY WAS TESTED AND VERIFIED AT THE SET POINT OF 450 PSIG. DISASSEMBLY OF THE FISHER 6358EBH PILOT DISCOVERED A FAILED O-RING UNDER THE DIAPHRAGM. THE FAILED O-RING IS ATTRIBUTED TO THE PREMATURE OPERATION OF THE RELIEF VALVE. A TREND OF THE FUEL RUN PRESSURE WAS REVIEWED AND A PRESSURE DROP WAS OBSERVED AT 15:52 HOURS ON 4/4/15. WE DETERMINED THIS WAS THE TIME THAT THE RELIEF VALVE STARTED VENTING. THE SCADA SYSTEM HAD A HIGH ALARM SET AT 490 PSIG AND THE PRESSURE NEVER EXCEEDED 435 PSIG, SO NO ALARM NOTIFICATION WAS RECEIVED. THE ALARM HAS BEEN ADJUSTED TO 425 PSIG TO PREVENT FUTURE OCCURANCES WITH NO ALARM NOTIFICATIONS.

PHMSA trend classification: not significant, not serious.

PHMSA standardized cause: EQUIPMENT FAILURE — OTHER EQUIPMENT FAILURE.

PHMSA indexed costs: $9,940 reported total cost, $8,603.856 in 1984 dollars, $11,456.279 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.