SOUTHERN NATURAL GAS CO

Incident Narrative

ON DECEMBER 26, 2020, SOUTHERN NATURAL GAS COMPANY (SNG) COMPRESSOR STATION KNOWN AS ELLERSLIE COMPRESSOR STATION ON THE SOUTH MAIN SYSTEM NEAR MILEPOST 311 EXPERIENCED AN EMERGENCY SHUT DOWN (ESD) EVENT. AT 05:19-HOURS, GAS CONTROL RECEIVED A SCADA ALARM. THE CONTROLLER ON DUTY, USING THE CALL-OUT SYSTEM, NOTIFIED THE PROPER OPERATIONS PERSONNEL AT THAT TIME. AT 06:04-HOURS, OPERATIONS PERSONNEL ARRIVED AT ELLERSLIE COMPRESSOR STATION AND CONFIRMED NATURAL GAS WAS VENTING. UPON SAFELY ENTERING THE COMPRESSOR STATION PROPERTY, THE OPERATIONS PERSONNEL BEGAN INSPECTING THE COMPRESSOR STATION TO DETERMINE WHY NATURAL GAS WAS STILL VENTING FOLLOWING THE ESD FUNCTION. OPERATIONS PERSONNEL FOUND VALVE #19 WHICH IS PART OF THE ESD SYSTEM LOCATED IN THE SUCTION SIDE OF THE STATION PIPING, HAD NOT FULLY CLOSED. OPERATIONS PERSONNEL MANUALLY CLOSED VALVE #19 AND THE STATION WAS SHUT DOWN AT 6:30-HOURS. FIELD OPERATIONS INITIATED THE EMERGENCY RESPONSE LINE (ERL) PROCESS FOLLOWING INTERNAL PROCEDURES AND THE INCIDENT WAS DEEMED REPORTABLE DURING THE ERL CALL. AS PART OF SNG'S POST INCIDENT INVESTIGATION PROCESS THE OPERATIONS PERSONNEL ON SITE DISCOVERED AN EXIT POINT IN THE COMPRESSOR STATION YARD WITH SOME ICE FORMED NEAR AN UNDERGROUND ESD FACILITY PIPE. SNG STARTED THE EXCAVATION PROCESS TO IDENTIFY THE SOURCE OF THE UNDERGROUND LEAK. AFTER EXPOSING THE UNDERGROUND ESD PIPE, SNG DISCOVERED THAT THE 1/2-INCH ESD PIPE HAD A CRACK IN A THREADED CONNECTION. DURING THE ROOT-CAUSE ANALYSIS IT WAS DETERMINED THAT THE CRACKED UNDERGROUND ESD PIPE WAS THE CAUSE OF THE ESD EVENT. FURTHERMORE, THE ANALYSIS ALSO REVEALED THAT VALVE #19 DID NOT FULLY CLOSE AS DESIGNED ALLOWING THE VOLUME OF GAS RELEASED TO BE ABOVE THE PHMSA REPORTABLE THRESHOLD. OPERATIONS MANAGEMENT EXPEDITED A CONTRACTOR TO COME ON SITE AND REPAIR THE BURIED 1/2-INCH ESD LINE. THE CRACKED PIPE WAS SENT TO A LAB FOR FURTHER ASSESSMENT AND THE LINE REPAIR WAS COMPLETED ON DECEMBER 26, 2020. OPERATIONS PERSONNEL CHECKED AND CYCLED VALVE #19 WITH NO ISSUE. VALVE #19 IS CLOSED AND LOCKED OUT OF SERVICE. SNG OPERATIONS HAS ORDERED A NEW SHAFER OPERATOR FOR 2021 INSTALLATION. WITH GENERAL SAFETY INSPECTION OF THE COMPRESSOR STATION AND COORDINATION WITH GAS CONTROL, THE COMPRESSOR STATION RETURNED TO SERVICE AT 22:15-HOURS, DECEMBER 26, 2020. THE LABORATORY ANALYSIS OF THE 1/2-INCH ESD LINE PIPE SPECIMEN DETERMINED THE CRACK OCCURRED BECAUSE OF HIGH CYCLE, LOW NOMINAL STRESS BENDING FATIGUE INITIATING IN THE ROOT OF THE THREADS. THE ANALYSIS ALSO NOTED THE STEEL PIPE CHEMISTRY DID NOT MEET ASTM A53 GRADE B STANDARDS DUE TO HIGHER PHOSPHORUS CONTENT. HOWEVER, TESTING FOUND THE TENSILE STRENGTH OF THE STEEL MEETS THE MINIMUM REQUIREMENTS OF ASTM A53 GRADE B. THE 1/2-INCH ESD LINE WAS PROMPTLY REPAIRED TO RETURN THE STATION TO SERVICE.