CENTERPOINT ENERGY GAS TRANSMISSION

Incident Narrative

ON 01/11/11 AT 17:30 A THIRD PARTY CALLED CEGT SYSTEM CONTROL AND REPORTED A PIPELINE BLOWOUT OFF OF FM-31 TRAVELING SOUTH ON FM-31 FROM DEBERRY, TX ON LEFT SIDE OF ROAD ABOUT 1 MILE NORTH OF FM-123. AT 17:35 CEGT SYSTEM CONTROL DISPATCHED A CEGT FIELD TECHNICIAN TO INVESTIGATE AND VERIFY THE LEAK. AT 20:05 CEGT TECHNICIANS REPORTED TO SYSTEM CONTROL THAT THE LEAK IS JUST OFF A DIRT ROAD WITH TWO ENTRANCES. THE LEAK IS IN THE WOODS WITH NO STRUCTURES IN THE AREA OR, BUT GAS WAS BLOWING ACROSS THE ROAD. IT WAS STILL NOT DETERMINED IF THE LEAK BELONG TO CEGT AND SINCE IT WAS DARK IT WAS DECIDED TO MONITOR THE LOCATION OVER NIGHT. AT 20:50 CEGT TECHNICIANS REPORTED TO SYSTEM CONTROL THAT BOTH ENTRANCES TO THE DIRT ROAD LEADING INTO THE LEAK ARE BLOCKED OFF AND WILL BE MANNED OVER NIGHT. ON 01/12/2011AT 07:53 SYSTEM CONTROL AND OPERATIONS HELD A CALL TO PLAN THE STEPS NEEDED TO DETERMINE IF THE LEAK WAS ON A CEGT PIPELINE. AT 10:15 SYSTEM CONTROL NOTIFIED NRC OF THE LEAK AND INDICATED CEGT WAS IN THE PROCESS OF DETERMINING IF THE LEAK WAS ON CEGT'S PIPELINE. AT 10:45 VALVES WERE SHUT ISOLATING THE PIPELINE SEGMENT WITH THE POSSIBLE LEAK AND IT WAS DETERMINED THAT THE LEAK WAS ON CEGT'S SYSTEM. VALVES WERE OPENED BACK UP, BUT THE PRESSURE WAS REDUCED FROM 300 LB. TO 250 LB. DUE TO A SIGNIFICANT LOAD IN SHREVEPORT AND THE SURROUNDING AREA, LOWERING THE PRESSURE WAS THE CHOSEN COURSE OF ACTION UNTIL NOTIFYING CUSTOMERS OF THE NEED TO REDUCE THEIR TAKES. CEGT CONTACTED THE LARGE INDUSTRIAL CUSTOMERS IN THE AREA TO REQUEST THEY REDUCE THEIR TAKES AND TO NOTIFY THEM THAT THEY MAY SEE LOWER PRESSURES BEGINNING AT 13:00. AT 16:00 THE LINE WAS BLOWN DOWN FROM 250# TO ZERO. A 26 FOOT SECTION OF THE PIPELINE WAS REMOVED AND REPLACED WITH TESTED EMERGENCY PIPE. AT 21:00 X-RAYS WERE COMPLETE THE LINE WAS PURGED AND PACKED. CONTROL OF THE PIPELINE WAS GIVEN BACK TO SYSTEM CONTROL AT 22:15. THE SECTION OF PIPE REMOVED THAT WAS REMOVED AND SENT TO KIEFNER & ASSOCIATES FOR METALLURGICAL ANALYSIS. THE CONCLUSION IS AS FOLLOWS: THE FAILURE WAS CAUSED BY A BUCKLE THAT FORMED IN THE PIPE WALL FROM COMPRESSIVE AXIAL OR BENDING STRESS ON THE PIPELINE. IT IS NOT KNOWN WHEN OR HOW THE BUCKLE WAS FORMED. THE FAILURE WAS CAUSED BY AXIAL TENSILE STRESS ACTING ON THE BUCKLED PIPE WHICH RESULTED IN A CIRCUMFERENTIALLY ORIENTED FRACTURE IN THE BOTTOM QUADRANT OF THE PIPE THAT EXTENDED FROM THE 3 TO 9 OCLOCK PIPE POSITIONS. BECAUSE THE FRACTURE PROPAGATED AFTER PENETRATING THE PIPE WALL, IT IS CLASSIFIED AS A RUPTURE RATHER THAN A LEAK, EVEN THOUGH THE PIPELINE WAS NOT COMPLETELY SEPARATED. THE BUCKLE WAS POSITIONED IN AN AREA OF REDUCED WALL THICKNESS NEAR THE END OF A JOINT OF PIPE A FEW INCHES AWAY FROM A GIRTH WELD. THE GIRTH WELD ITSELF WAS NOT INVOLVED IN THE FAILURE. THE CURVATURE STRAIN WITH THE BUCKLES PROFILE WAS DETERMINED TO BE 9 PERCENT USING THE TEMPLATE OVERLAY METHOD , WHICH EXCEEDS THE 6 PERCENT STRAIN SAFE LIMIT. THE PIPE JOINT WHICH CONTAINED THE FAILURE MET THE REQUIREMENTS OF THE APPROPRIATE EDITION OF API 5L. NO OTHER DEFECTS WERE PRESENT NEAR THE FAILURE ORIGIN. LAB ANALYSIS CONCLUDE THAT THE PIPE JOINT SPECIMEN CONTAINING THE FAILURE MET THE REQUIREMENTS OF THE APPROPRIATE EDITION OF API 5L. TENSILE TEST RESULTS SHOWED A YIELD STRENGTH OF 41.800 PSI/API 5L REQUIREMENTS OF 30,0000 MINIMUM. API STD 5L, TENTH EDITION, AUGUST 1944 FOR LAP-WELDED, BESSEMER LINE PIPE.