NORTHERN NATURAL GAS CO

Incident Narrative

ON AUGUST 7, 2012 AT APPROXIAMTELY 9:15 A.M. LOCAL TIME A SECTION OF 10-INCH DIAMETER PIPELINE IDENTIFIED AS RDU30801 NEAR MILE POST 0.34 AT THE REDFIELD, IOWA UNDERGROUND STORAGE FACILITY RUPTURED. THE PIPELINE FAILURE RESULTED IN A FIRE WHICH WAS EXTINGUISHED AT 10:51 A.M. LOCAL TIME WHEN THE FAILED SECTION OF PIPELINE WAS ISOLATED. EMERGENCY RESPONDERS FROM DALLAS COUNTY IOWA SECURED THE AREA UNTIL THE FIRE WENT OUT. PRESSURE ON THE LINE AT THE TIME OF THE FAILURE WAS APPROXIMATELY 1,254 PSI. THE MAXIMUM ALLOWABLE OPERATING PRESSURE FOR THE PIPELINE IS 1,385 PSI. INTERNAL CORROSION IS BELIEVED TO BE THE ROOT CAUSE OF THE PIPELINE FAILURE. THERE WERE NO INJURIES, NO EVACUATIONS AND NO LOSS OF SERVICE TO CUSTOMERS. TWO MIDAMERICAN ENERGY COMPANY UTILITY POWER POLES WERE DAMAGED. THE RUPTURE MEASURED APPROXIMATELY 48 FEET 4-INCHS IN LENGTH. A SECTION OF THE DAMAGED PIPE WAS IDENTIFIED AS THE RUPTURE ORIGIN. THE LINE OF FRACTURE TRAVELED LONGITUDINALLY THROUGH A SECTION OF CORRODED PIPE APPROXIMATELY 12-INCHS IN LENGTH. THE INTERNAL CORROSION OCCURRED AT THE 6 O'CLOCK POSITION WITH ABOUT 90% WALL LOSS. THE INVESTIGATION INDICATED THE FRACTURE EXTENDING WEST FROM THE RUPTURE SITE STOPPED AT A GIRTH WELD. THE FRACTURE EAST ENDED IN THE MIDDLE OF THE JOINT. NO EXTERNAL CORROSION OR EVIDENCE OF THIRD-PARTY DAMAGE WAS FOUND. THE INCIDENT WAS REPORTED TO THE NATIONAL RESPONSE CENTER (TICKET NUMBER 1020240) DATED 07-AUG-12. THE INCIDENT WAS ALSO REPORTED TO THE IOWA UTILITIES BOARD IN DES MOINES, IOWA AND THE PIPELINE AND HAZARDOUS MATERIALS SAFETY ADMINISTRATION IN KANSAS CITY. ADDITIONAL INVESTIGATION IS IN PROGRESS AS WELL AS FOLLOW UP ANALYSIS BY OUTSIDE LABORATORIES. IN ORDER TO ENSURE THAT THERE ARE NOT SIMILAR ISSUES REMAINING AT THE FACILITY NORTHERN IS NOW CONDUCTING IN-LINE INSPECTION OF SIMILAR PIPELINE SEGMENTS AT THE FACILITY. BAKER HUGHES IS THE INLINE INSPECTION CONTRACTOR. SUPPLEMENTAL/FINAL: SECTION 15 ENTERED DATE AND TIME OF RETURN TO SERVICE, PART B ITEM 11, CORRECTED DEPTH-OF-COVER, PART D ITEM 7 ENTERED FINAL ESTIMATED PROPERTY DAMAGE COSTS (7A THROUGH 7E). PART G ENTERED CAUSE OF INTERNAL CORROSION. APPROXIMATELY 108 FEET OF NEW COATED 10-INCH PIPE WAS INSTALLED AT THE RUPTURE SITE. AN ILI OF THE COMPLETE LINE WAS COMPLETED, WHICH RESULTED IN AN APPROXIMATE REPLACEMENT OF AN ADDITIONAL 100 FEET OF COATED 10-INCH PIPE. THE COMPLETE LINE WAS SUCCESSFULLY HYDRO-TESTED. THE LINE WAS PURGED AND PUT BACK INTO SERVICE AT APPROXIMATELY 13:30 ON SEPTEMBER 15, 2012. SUPPLEMENTAL/FINAL: UPDATED REPORT PER PHMSA REQUEST TO INDICATE TRANSMISSION IN E5F ON REPORT 20120086 DATED 8/28/2012.