NORTHERN NATURAL GAS CO
gas_transmission Incident —
Incident Information
| Report Date | — |
| Operator | NORTHERN NATURAL GAS CO |
| Commodity | — |
| Pipeline Type | gas_transmission |
Location
| State | |
| Coordinates | 40.90005, -96.17875 |
Cause
| Cause | EQUIPMENT FAILURE |
| Subcause | — |
Casualties
| Fatalities | 0 |
| Injuries | 0 |
Costs
| Property Damage | — |
| Lost Commodity | — |
| Public/Private Damage | — |
| Emergency Response | — |
| Environmental Remediation | — |
| Other Costs | — |
Location Map
Incident Narrative
ON SEPTEMBER 19, 2018, OPERATIONS PERSONNEL WERE MAKING PLANED PRESSURE ADJUSTMENTS TO THE OMAHA 3RD BRANCH LINE TO RAISE PRESSURE FROM 725 TO 775 PSIG. THE MAOP IS 800 PSIG. WHEN PRESSURE REACHED 750 PSIG, THE RELIEF VALVE BEGAN TO VENT. OPERATIONS PERSONNEL ISOLATED THE RELIEF VALVE AND THE VENTING STOPPED. VENTING OCCURRED FOR APPROXIMATELY 5 MINUTES. APPROXIMATELY 3,869 MCF OF GAS WAS RELEASED. THE CAUSE OF THE RELIEF VALVE TO VENT BELOW SET POINT WAS VIBRATION CREATED BY THE V250 CONTROL VALVE AND THE FACILITY PIPING. THE ENERGY TRANSFERRED IN THE FORM OF VIBRATION OVER TIME LOOSENED THE LOCKING NUT ON THE PILOT SET POINT ADJUSTMENT STEM. THIS ALLOWED THE STEM TO BACK OUT, CHANGING (LOWERING) THE SET POINT. CONTRIBUTING CAUSES MAY HAVE BEEN THE INCREASED CONTROL VALVE NOISE LEVEL DUE TO A CHANGE IN OPERATING PRESSURES (INCREASED PRESSURE DROP DURING CONSTRUCTION ACTIVITIES) AND/OR INSUFFICIENT TORQUE ON THE LOCK NUT WHEN PREVIOUSLY TESTED. ADDITIONAL IMPACT TO THE RELIEF VALVE ASSEMBLY WAS DUE TO THE IMPROPER DESIGN OF THE VENT PIPING AND SUPPORT STRUCTURE, WHICH ENHANCED THE SIDE THRUST WHEN THE RELIEF VALVE OPENED.
About This Pipeline Incident
Pipeline incident data is reported to the Pipeline and Hazardous Materials Safety Administration (PHMSA). All significant incidents involving fatalities, injuries, or property damage over $50,000 must be reported.