PHMSA Report 20140070 - NORTHERN NATURAL GAS CO — Gas transmission and gathering — incident on 2014-06-05 | Regulus

Gas transmission and gathering incident in DES MOINES, POLK County, IA. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 6392 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: 20140070.

Operator ID: 13750.

Reported incident date: 6/5/2014 8:15.

Location detail: 2777

Cause detail: MALFUNCTION OF CONTROL/RELIEF EQUIPMENT

Cause detail: DURING A CONSTRUCTION PROJECT TO REPLACE A RELIEF VALVE, THE NEW VALVE VENTED APPROXIMATELY 6.4 MMCF IN NATURAL GAS. THE INVESTIGATION CONCLUDED THAT THERE WAS GAS SEEPAGE BY THE CONTROL VALVES THAT CAUSED THE DOWNSTREAM PRESSURE TO REACH 130 PSIG, RESULTING IN THE ACTIVATION OF THE NEW RELIEF VALVE. THIS BUILDUP IN PRESSURE WAS CONCLUDED TO OCCUR BETWEEN THE FIVE MINUTE SCANS BEFORE 0820 HOURS ON JUNE 5, 2014. IT WAS CONCLUDED THAT THE SEATS ON THE CONTROL VALVES WERE THE CAUSE OF THE VALVES NOT HOLDING, WHICH HAVE SINCE BEEN REPLACED. ADDITIONAL OUTSIDE CONDITIONS MAY HAVE CONTRIBUTED TO THE EVENT, BUT ARE NOT THE ROOT CAUSE. DURING THE INSTALLATION OF A RELIEF STACK TO THE NEW RELIEF VALVE, VIBRATION OF THE INSTALLATION MAY HAVE ADJUSTED THE SET POINT OF THE RELIEF VALVE. IT WAS CONCLUDED THAT THE VIBRATION OF THE RELIEF VALVE POPPING OPEN AND CLOSED DID WALK THE SET SCREW OUT FROM 0820 TO 1100 HOURS WHEN THE INVESTIGATIVE TEAM HEARD A DISTINCTIVE SOUND DIFFERENCE IN THE RELIEF VALVE VENTING. AFTER THE SOUND OF GAS VENTING CHANGED, A TECHNICIAN NOTICED THE SET SCREW FOR THE RELIEF VALVE ON THE GROUND AT 1100 HOURS. THE INVESTIGATIVE TEAM RE-INSERTED THE SET SCREW AND REPAIRED THE CONTROL VALVES BEFORE RETURNING THE DELIVERY POINT BACK INTO SERVICE.

PHMSA trend classification: not significant, not serious.

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

PHMSA indexed costs: $34,229 reported total cost, $22,875.523 in 1984 dollars, $30,817.06 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.