NORTHERN NATURAL GAS CO

Incident Narrative

ON DECEMBER 23, 2011, AT 8:58 A.M., THE CLIFTON COMPRESSOR STATION EXPERIENCED AN UNPLANNED EMERGENCY SHUTDOWN DUE TO A SEAL OIL FIRE IN COMPRESSOR BUILDING 5. THE SEAL OIL FIRE OCCURRED ON UNIT 31, A G.E. FRAME III 9100-HORSEPOWER TURBINE COMPRESSOR, BETWEEN THE UNIT POWER TURBINE AND THE COMPRESSOR. THE FIRE AND GAS DETECTION SYSTEM DETECTED THE SEAL OIL FIRE IMMEDIATELY AND ACTIVATED THE STATION EMERGENCY SHUTDOWN SYSTEM, WHICH FUNCTIONED AS DESIGNED AND SAFELY SHUT DOWN THE UNIT AND THE STATION. ALL EMERGENCY VALVES TRAVELED TO THE CORRECT POSITION FOLLOWING ACTIVATION. THE ELECTRICAL POWER TO UNIT 31 WAS MANUALLY ISOLATED AND LOCKED OUT BY OPERATIONS PERSONNEL, AS IT IS NOT TRIPPED BY THE EMERGENCY SHUTDOWN SYSTEM. THIS IS BY DESIGN TO AVOID CATASTROPHIC DAMAGE TO THE TURBINES, DUE TO LACK OF LUBE OIL DURING POST-TRIP SPIN DOWN. AFTER ENSURING CONDITIONS WERE SAFE, CLIFTON VOLUNTEER FIRE DEPARTMENT PERSONNEL ENTERED THE BUILDING AND EXTINGUISHED THE RESIDUAL BURNING SEAL OIL. UNIT 31 WAS ON-LINE DECEMBER 23, 2011, WHEN THE FITTING FAILURE OCCURRED. ON DECEMBER 22, 2011, AT 3:45 P.M., OPERATIONS PERSONNEL PERFORMED A DAILY WALK THROUGH WHILE THE UNIT WAS DOWN AND NO ABNORMAL CONDITIONS WERE IDENTIFIED. THE UNIT WAS STARTED REMOTELY BY GAS CONTROL AT 3 A.M. DECEMBER 23, 2011, AND NO WALK THROUGH WAS CONDUCTED BEFORE THE 8:58 A.M. SHUTDOWN. THE FITTING THAT FAILED IS BELIEVED TO BE PART OF THE ORIGINAL 1970 INSTALLATION. THE CAUSE OF THE FIRE WAS DUE TO A FAILURE IN THE THREADED 1-INCH-DIAMETER END OF A 2- TO 1-INCH-DIAMETER SWEDGE FITTING, THAT THREADED INTO THE BOTTOM OF THE SEAL OIL PRESSURE REGULATOR. THE FITTING FAILURE ALLOWED HIGH PRESSURE COMPRESSOR SEAL OIL TO SPRAY ONTO THE BACK OF THE TURBINE EXHAUST AND IGNITE. SUPPLEMENTAL/FINAL REPORT TO ORGINAL REPORT NO. 20120010 - 15427, REPORT DATE 01/20/2012 - A METALLURICAL ANALYSIS OF THE FAILURE OF THE THREADED FITTING BY AN OUTSIDE METALLURICAL LABORATORY INDICATES THAT THE ROOT CAUSE WAS FROM THE FITTING BEING IN STRESS BINDING POSITION AND METAL FATIGUE OF THE THREADS. THIS EVENT IS CONSIDERED COMPLETE WITH NO FUTHER ACTIONS PENDING OR PLANNED. SUPPLEMENTAL/FINAL: UPDATED REPORT 20120010 DATED 1/20/2012 PER PHMSA REQUEST BY INDICATING IN PART E5F TRANSMISSION.