ENABLE GAS TRANSMISSION, LLC

Incident Narrative

ON MARCH 26TH, 2020 AT 13:15 ENABLE GAS TRANSMISSION LINE N EXPERIENCED A FAILURE IN CADDO PARISH LOUISIANA. THE FAILED SECTION WAS LOCATED IN A SEASONAL CREEK 12"" UNDERGROUND AND THE FAILURE OCCURRED NEAR THE 12 O'CLOCK AREA OF THE PIPE. THE FAILED SECTION WAS REMOVED AND SENT TO PRECISION ENGINEERING FOR METALLURGICAL ANALYSIS. THE NRC WAS NOTIFIED ON 3/26/2020 (NRC # 1274308). A 48 HR FOLLOW UP CALL WAS PROVIDED TO THE NRC ON 3/28/2020 (NRC # 1274411). ENABLE MIDSTREAM PARTNERS HAS NOT RECEIVED THE RESULTS OF THE LAB ANALYSIS. THE FAILURE INVESTIGATION IS ON-GOING. _______________________________________________________________________________________________________________________THE LAB ANALYSIS PERFORMED ON THE RUPTURED LINE PIPE INDICATE THAT THE INITIATION OF THE FRACTURE WAS DUE TO DUCTILE OVERLOAD. THE WALL THICKNESS OF THE LINE PIPE IN THE REGION OF THE FACTURE WAS FOUND TO HAVE BEEN REDUCED DUE TO HEAVY O.D. CORROSION AT THE 12 O'CLOCK POSITION (TOP OF LINE). THE WALL IN THIS REGION WAS REDUCED (WALL THICKNESS RANGING FROM 0.013 INCH TO 0.088 INCH MEASURED NEAR RUPTURE) TO THE POINT WHERE IT COULD NO LONGER SUPPORT THE HOOP STRESS GENERATED BY THE INTERNAL LINE PRESSURE (225 PSIG). BY USING THE BARLOW'S FORMULA AND THE TENSILE STRENGTH OBTAINED IN THE MECHANICAL TESTING, IT IS CALCULATED THAT WITH AN INTERNAL PRESSURE OF 225 PSIG AND A TENSILE STRENGTH OF 66,542 PSI, RUPTURE WOULD BE EXPECTED TO OCCUR AT A WALL THICKNESS OF APPROXIMATELY 0.027. THE ANALYSIS PERFORMED ON THE FAILED SECTION OF LINE N SHOW EXTENSIVE O.D. CORROSION OF THE TOP PORTION OF THE PIPE. WALL THICKNESS MEASUREMENTS CONFIRMED THE WALL LOSS WAS CONFINED TO THE 12 O'CLOCK POSITION OF THE PIPE. THIS SECTION OF LINE N WAS LOCATED IN A SEASONAL CREEK AREA WHERE THE PIPE IS BELIEVED TO HAVE BEEN 8-12 INCHES BELOW THE SURFACE PRIOR TO FAILURE. WHEN FULLY EVACUATED, STANDING WATER COULD BE SEEN INSIDE THE FAILED PIPE SEGMENT. THE GAS IN LINE N IS TARIFF QUALITY GAS INDICATING WATER WAS PRESENT ABOVE THE PIPE PRIOR TO RUPTURE. IT IS DETERMINED THAT 70 YEARS OF SEASONAL EXPOSURE TO WATER AND ATMOSPHERE, WITH COATING DETERIORATION AT THE 12 O'CLOCK POSITION, REDUCED THIS SECTION OF PIPE TO WHERE IT COULD NO LONGER SUPPORT THE HOOP STRESS GENERATED BY THE INTERNAL LINE PRESSURE (225 PSIG). ______________________________________________________________________________________________________________________ THE FAILED SECTION OF LINE HAS NEVER BEEN EXPOSED. ALONG WITH ANNUAL PATROLS THERE HAVE BEEN ADDITIONAL EXPOSURE INSPECTIONS ON THIS LINE. A CLOSE INTERVAL SURVEY WAS PERFORMED IN 2016 AND THE CREW DID NOT SEE ANY PIPE EXPOSED AND IN 2018 THE OPS SOUTHERN DIVISION LAUNCHED AN EXPOSED PIPE INITIATIVE. DURING THIS INITIATIVE THE FAILED SECTION WAS NOT SEEN OR DETERMINED TO BE EXPOSED. THERE WAS AN EXPOSURE ROUGHLY 700 FEET TO THE NORTH OF THE FAILURE SITE THAT WAS DISCOVERED IN 2006. THE EXPOSURE WAS ENTERED INTO MAXIMO, WORK ORDERS FOR INSPECTION WERE REGENERATED, AND THE COATING WAS REPAIRED IN 2013. THE SITE CONTINUES TO BE INSPECTED TODAY WITH WORK ORDERS BEING GENERATED FOR FOLLOW UP. IF THE FAILED SECTION WAS ABOVEGROUND, OR VISIBLE, WE WOULD HAVE SEEN IT. THE EXPOSURE WOULD HAVE FOLLOWED THE SAME INSPECTION PROCESS AS THE EXPOSURE 700 FEET DOWNSTREAM. MOST LIKELY THE FAILURE SITE HAS ALWAYS BEEN COVERED BY WATER AND A SMALL AMOUNT OF SOIL. WHEN THE FAILED SECTION WAS REPLACED TAPE COULD BE SEEN ON THE PIPE THROUGH THE ENTIRE EXCAVATION (ROUGHLY 90'). ALSO, IN LOOKING AT EXPOSED SECTIONS OF ORIGINAL LINE N PIPE, THE TAPE HAS BEEN PRESENT AT OTHER LOCATIONS AS WELL. TAPE WAS NOTED ON DOCUMENTATION FOR THE EXPOSURE MENTIONED ABOVE, AS WELL AS, SEEN ON A DIRECT ASSESSMENT DIG NEAR THE SHREVEPORT AREA. DUE TO THE ABOVE EXAMPLES THE TEAM BELIEVES THE TAPE IS PART OF ORIGINAL CONSTRUCTION.