NORTHERN NATURAL GAS CO

Incident Narrative

ON OCTOBER 8, 2013 AT APPROXIMATELY 10:40 PM (22:40) NORTHERN'S 30-INCH BEAVER TO MULLINVILLE (OKM10703-M680C) C-LINE FAILED. THE FAILURE RESULTED IN A RELEASE OF NATURAL GAS AND A SUBSEQUENT FIRE. THE FAILURE OCCURRED IN A CULTIVATED FIELD LOCATED IN HARPER COUNTY, OKLAHOMA NEAR MILE POST 34.22. THE AREA IS WEST OF US HIGHWAY 283 AND SOUTH OF E0040 ROAD. THE FAILURE DID NOT CAUSE ANY INJURIES OR EVACUATIONS. WHILE THE FIRE DESTROYED SOME CROPS, NO OTHER PROPERTY DAMAGE WAS REPORTED. NORTHERN'S SHIFT OPERATOR LOCATED AT THE BEAVER COMPRESSOR STATION DISCOVERED THE PRESSURE ON THE BEAVER TO MULLINVILE M680C LINE WAS DECREASING AT AN ABNORMAL RATE. HE WAS ALSO ABLE TO SEE THE FIRE IN THE DISTANCE. THE FAILED SECTION WAS SUBSEQUENTLY ISOLATED WHEN THE UPSTREAM AND DOWNSTREAM MAINLINE VALVES WERE CLOSED. THE INVESTIGATION TEAM BEGAN TO EXAMINE THE SITE AND COLLECT EVIDENCE ON OCTOBER 9. THE FAILURE HAD OPENED A HOLE ALONG THE RIGHT-OF-WAY ABOUT 45 FEET AT ITS WIDEST AND 200 FEET LONG. SEVERAL SECTIONS OF PIPE HAD BEEN EJECTED FROM THE DITCH. ALL OF THE FAILED PIPE WAS SENT TO STRESS ENGINEERING SERVICES IN HOUSTON, TEXAS FOR EXAMINATION. THE PIPE WAS RECEIVED IN HOUSTON ON OCTOBER 13. STRESS DETERMINED THAT THE FAILURE WAS A DIRECT RESULT OF AN AREA OF EXTERNAL CORROSION ABOUT 9 INCHES LONG BY 3 INCHES CIRCUMFERENTIALLY. ON OCTOBER 16, 2013, NORTHERN RECEIVED APPROVAL FROM THE SW REGION OF PHMSA TO RETURN THE PIPELINE TO SERVICE.