ENABLE OKLAHOMA INTRASTATE TRANSMISSION, LLC

Incident Narrative

ON 7/26/2019 AT 06:10 RATE OF CHANGE ALARMS ALERTED THE SYSTEM CONTROLLER OF A POSSIBLE SITUATION WITH LINE 7. THE CONTROLLER STARTED TO DISPATCH O&M TECHS TO INVESTIGATE THE CAUSE OF THE ALARMS. AT 6:20 A LANDOWNER CALLED SYSTEM CONTROL TO NOTIFY OF A JET ENGINE NOISE ON HIS PROPERTY. O&M TECHNICIANS DISCOVERED THE RUPTURE SITE TO BE ON A LARGE RANCH NEAR HOMINY, OKLAHOMA. THE AREA IS A CLASS 1 LOCATION AND THERE WERE NO INJURIES, EVACUATIONS, FIRES, OR FATALITIES. VALVES WERE SHUT AND THE LINE WAS ISOLATED AT 07:57. THE NRC WAS NOTIFIED ON 7/26/19 AT 07:47 (NRC# 1253231). A 48 HOUR FOLLOW UP CALL WAS PROVIDED TO THE NRC ON 7/27/19 AT 15:57 (NRC# 1253370). THE FAILED SECTION OF PIPE WAS REMOVED AND SENT TO A LAB FOR METALLURGICAL ANALYSIS. THE RESULTS OF THE METALLURGICAL FAILURE EXAMINATION INDICATED: -THE PIPE FAILED DUE TO NEAR NEUTRAL STRESS CORROSION CRACKING FROM A BREAK IN THE OD SURFACE COATING THAT ALLOWED THE PIPE TO BE EXPOSED TO THE ELEMENTS. -STRAIGHT, WIDE CRACKS WERE OBSERVED WITH VERY LITTLE BRANCHING. THESE ARE A HALLMARK FEATURE OF NEAR-NEUTRAL STRESS CORROSION CRACKING. -EXPOSURE TO THE ELEMENTS CAUSED PITTING CORROSION, WHICH ACTED AS NUCLEATION SITES FOR STRESS CORROSION CRACKING. -THE FAILURE INITIATION REGION EXHIBITED A PRE-EXISTING CRACK THAT HAD PROPAGATED APPROXIMATELY 80% OF THE PIPE WALL THICKNESS AT THE TIME OF FAILURE. -IN ADDITION, THE OD SURFACE OF THE PIPE EXHIBITED A COLONY OF CRACKS PROPAGATING PARALLEL TO THE FRACTURE SURFACE. THE REGIONS OF THE PIPE IMMEDIATELY ADJACENT TO THE FAILURE INITIATION REGION DID NOT EXHIBIT PITTING CORROSION, INDICATING THAT THE INITIAL REGION OF COATING DAMAGE WAS SMALL AND LOCALIZED. 10/1/2019 SUPPLEMENTAL REPORT PART G.5.1 UPDATED TO DETERMINED BY METALLURGICAL ANALYSIS PART G.5.3 UPDATED TO STRESS CORROSION CRACKING PART H NARRATIVE UPDATED TO INCLUDE METALLURGICAL RESULTS