NORTHERN NATURAL GAS CO

Incident Narrative

ON JANUARY 10, 2010, AT APPROXIMATELY 21:24 P.M. A FIRE WAS DISCOVERED, BY A NORTHERN NATURAL GAS COMPANY EMPLOYEE, AT THE REDFIELD UNDERGROUND STORAGE FIELD, LOCATED NEAR REDFIELD, IOWA, IN THE SL PETER UNDERGROUND STORAGE FORMATION AT WHAT IS CALLED THE MAHER #3 WELL SITE IN SECTION 12, T19N, R29W, DALLAS COUNTY, IOWA. THERE WAS NO EXPLOSION, NO INJURIES, NO EVACUATIONS AND NO LOSS OF SERVICE TO CUSTOMERS. AT APPROXIMATELY 24:00 HOURS THE ST PETER FORMATION PIPELINE SYSTEM PORTION, OF THE STORAGE FIELD, WAS ISOLATED AND PRESSURE WAS BLOWN DOWN ON THE PIPING TO 5 PSIG TO ENABLE SAFE CLOSURE OF THE MAHER #3 WELL HEAD VALVE (SEE PAGE 2, ITEM 15A). THE FIRE WAS EXTINGUISHED BY 01:50 A.M. THE FIRE DESTROYED THE WELL HOUSE BUILDING AND ALL OF THE COMPONENTS WITHIN THE BUILDING BUT THE WELL HEAD VALVE AND PIPING WERE UNAFFECTED. THE PORTION OF THE ST. PETER PIPING, THAT WAS ISOLATED IN ORDER TO FACILITATE REDUCTION IN PRESSURE FOR THE CLOSURE OF THE MAHER #3 WELL HEAD VALVE, WAS RETURN TO NORMAL OPERATION PRESSURES AT APPROXIMATELY 12:00 A.M. ON MONDAY, JANUARY 11TH (SEE PAGE 2, ITEM 15B). PRELIMINARY RESULTS OF A POST INCIDENT INVESTIGATION IDENTIFIED THAT THE GAS LEAKAGE APPEARED TO BE FROM A BROKEN ONE-INCH UNION ON THE WELL SEPARATOR DRAIN LINE. THE UNION'S THREADS APPEARED TO BE STRIPPED OR PULLED. AT THE TIME OF THE EVENT THE AMBIENT TEMPERATURE WAS 21 DEGREES FAHRENHEIT AND THE WIND WAS OUT OF THE WEST AT APPROXIMATELY 14 MILES PER HOUR. IT IS POSSIBLE THAT FREEZING AND HEAVING MAY HAVE CREATING SUFFICIENT THERMAL STRESS WHICH CONTRIBUTED TO THE SEPARATION OF THE THREADS ON THE ONE-INCH UNION. THE NIGHT BEFORE THE FAILURE THERE WAS AN APPROXIMATE LOW TEMPERATURE OF - 19 DEGREES FAHRENHEIT IN THE AREA. ADDITIONAL METALLURGICAL FAILURE ANALYSIS IS BEING CONDUCTED TO ASSIST WITH DETERMINING WHETHER THERMAL STRESS FROM THE COLD TEMPERATURES COULD BE A ROOT CAUSE FOR STRIPPING OF THE THREADS AND THE UNION'S FAILURE. FINAL REPORT: A METALLURGICAL EXAMINATION OF THE FAILED ONE-INCH UNION INDICATED THAT TWO PORTIONS OF THE UNION'S THREADS DEMONSTRATED ROLLED DAMAGE TO THE TOP OF THE THREADS, WHICH INDICATES THE COMPONENT PULLED OVER THE PEAK OF THE THREAD AS IT DISENGAGED. AN EXAMINATION OF THE THREADS ALSO INDICATES ONE FLATTENED/ROUNDED LOCATION THAT MAY HAVE BEEN DAMAGED OR IMPROPERLY MACHINED PREVIOUS TO THE FAILURE. THE FITTING WAS INSTALLED IN 2006, AND MAY HAVE BEEN FAULTY AND THE FROZEN CONDITION OF THE DRAIN LINE, ON DECEMBER 10, 2010, MOST LIKELY CREATED THERMAL STRESS, WHICH RESULTED IN FAILURE OF THE FITTING. AS A MEASURE TO PREVENT RECURRENCE, ALL WELL SEPARATOR DRAIN LINES AT THE REDFIELD, IOWA UNDERGROUND STORAGE FACILITY WERE DISSEMBLED AND INSPECTED. NO OTHER ISSUES OR PROBLEMS WERE FOUND. THE FIRE APPEARS TO HAVE STARTED IMMEDIATELY AS THERE WAS NO INDICATION OF AN EXPLOSION. THE WIRING IN THE CONDUIT, STATIC ELECTRICITY OR SPARKS FROM THE BUILDING STRUCTURE OR THE ONE-INCH PIPE STRIKING OTHER PIPING WHEN IT SEPARATED WAS THE LIKELY IGNITION SOURCE. THIS EVENT IS CONSIDERED COMPLETE AND CLOSED. SUPPLEMENTAL/FINAL TO REPORT 20100019 PER PHMSA REQUEST IDENTIFIED PART E5F AS TRANSMISSION.