SOUTHERN NATURAL GAS CO

Incident Narrative

ON MARCH 23, 2015, A NATURAL GAS LEAK WAS DISCOVERED ON THE SOUTHERN NATURAL GAS SOUTH MAIN LINE LOOP AT THE INTERCONNECT WITH DSM CHEMICAL TAP. THE SOUTH MAIN LINE LOOP WAS DEPRESSURIZED AND REMOVED FROM SERVICE AND REPAIRS WERE INITIATED. A CRACKED WELD WAS DISCOVERED ON THE HOT TAP FITTING. THE SECTION OF PIPE CONTAINING THE HOT TAP ASSEMBLY WAS REPLACED WITH NEW PRETESTED SEGMENT OF PIPE. SNG WILL COMPLETE INSTALLATION OF A NEW HOT TAP ASSEMBLY. NO CUSTOMER SERVICE WAS IMPACTED BY THE INCIDENT. AN INVESTIGATION INTO THE ROOT CAUSE OF THE INCIDENT IS CURRENTLY UNDERWAY. THE METALLURGICAL REPORT REGARDING THE NPS 16 X NPS 6 HOT TAP FITTING AT THE DSM CHEMICAL METER STATION AT MP 491.127 IN RICHMOND COUNTY, GA ON THE SOUTHERN NATURAL GAS (SNG) SOUTH MAIN LOOP LINE WAS COMPLETED JUNE 2015. THE SIGNIFICANT CONCLUSIONS PRESENTED IN THE REPORT INCLUDED THE FOLLOWING: - THE HOT TAP FITTING LEAKED AT THE TOE OF THE CIRCUMFERENTIAL FILLET WELD JOINING THE FITTING TO THE IN-SERVICE PIPE. - THE LEAK WAS DUE TO A HYDROGEN CRACK AT THE TOE OF THE WELD. - THE UNUSUALLY HIGH CARBON EQUIVALENT OF THE IN-SERVICE PIPE WAS A SIGNIFICANT FACTOR CONTRIBUTING TO THE CRACKING. THE ROOT CAUSE INVESTIGATION IDENTIFIED THE UNUSUALLY HIGH CARBON EQUIVALENT OF THE IN-SERVICE PIPE AS A SIGNIFICANT FACTOR CONTRIBUTING TO THE CRACKING. A REVIEW OF AVAILABLE RECORDS WAS COMPLETED FOLLOWING THE ROOT CAUSE INVESTIGATION TO IDENTIFY ANY OTHER SEGMENTS ON THE SOUTH MAIN LOOP LINE, WITH SAME VINTAGE OF PIPE AND TAPS, THAT MAY EXIST AND REQUIRE FURTHER INVESTIGATION OR MONITORING. FROM A REVIEW OF THE AVAILABLE RECORDS, NO OTHER HOT-TAPS ON PIPE CONTAINING A HIGH CARBON EQUIVALENT WERE IDENTIFIED. FROM THIS REVIEW, SNG DETERMINED THAT OTHER TAPS OR CONNECTIONS WERE EITHER WELD-IN FITTINGS, WHICH ARE NOT AS PRONE TO HYDROGEN CRACKING, OR WERE INSTALLED ON A DIFFERENT VINTAGE OF PIPE.