SOUTHERN NATURAL GAS CO

Incident Narrative

THE MASTER FUEL GAS LINE AT THE PEARL RIVER COMPRESSOR STATION SUPPLIES FUEL GAS TO TWO (2) GENERAL ELECTRIC TURBINES, AN EMERGENCY ELECTRIC POWER GENERATOR, AND DOMESTIC HEAT FOR TWO (2) STATION BUILDINGS. ON JANUARY 16, 2015, A LOCAL RESIDENT REPORTED THE SOUND OF GAS AT THE STATION TO SOUTHERN NATURAL GAS PIPELINE COMPANY, LLC (SNG). SNG GAS CONTROL RESPONDED BY DISPATCHING A LOCAL SNG FIELD TECHNICIAN AND HE IMMEDIATELY ISOLATED THE FUEL GAS METER RUN TO STOP THE FLOW OF GAS SINCE HE OBSERVED THE RELIEF VALVE ON THE FIRST CUT OF THE MASTER FUEL RUN REPEATEDLY ACTIVATING AND RESETTING AT THE DESIGNATED SET-POINTS. IT SHOULD BE NOTED THAT THE STATION COMPRESSION WAS OFF-LINE DURING THE EVENT. THE RESPONDING FIELD TECHNICIAN OBSERVED ICE BUILD-UP ON THE FIRST-CUT, REGULATOR SENSING LINE WHICH CAUSED THE REGULATOR TO MALFUNCTION AND THE RELIEF VALVE TO ACTUATE. THE ESTIMATED GAS VOLUME RELEASED, USING METER STATION FLOW DATA, WAS 8,151 MSCF OVER A 23 HOUR PERIOD FROM 20:15 HOURS LOCAL TIME ON JANUARY 15, 2015 TO 19:05 HOURS LOCAL TIME ON JANUARY 16, 2015 WHEN SNG PERSONNEL ISOLATED THE FUEL METER STATION. THE RESULTS OF THE INVESTIGATION BY SNG, COMPLETED ON JANUARY 30, 2015, SHOWED THAT ALTHOUGH A FUEL GAS HEATER WAS INSTALLED TO HEAT FUEL GAS FOR THE COMPRESSOR STATION, WHEN THE STATION TURBINES ARE OFFLINE, THE RESULTING LOW FUEL GAS FLOW (FOR DOMESTIC PURPOSES ONLY) CAN ENABLE THE FUEL TEMPERATURE TO DROP, ESPECIALLY ON COLD DAYS, BEFORE THE GAS REACHES THE MASTER FUEL METER. SNG CONCLUDED THAT DURING EXTENDED PERIODS OF BELOW-FREEZING TEMPERATURES, WITH LOW FLOW, THE FUEL TEMPERATURE CAN DROP AND CAUSES ICE BUILD-UP ON THE REGULATOR PILOT SENSING LINE. SNG WILL COMPLETE THE FOLLOWING CORRECTIVE ACTIONS TO MINIMIZE THE EFFECTS OF FREEZING ON THE REGULATOR SENSING LINES AND INCREASE SITUATIONAL AWARENESS OF GAS RELEASE FROM OPP ON THE FUEL GAS SYSTEM: 1) INSTALLATION OF CATALYTIC HEATERS ON PILOT REGULATOR SENSING LINES TO PREVENT ICE BUILD-UP DURING CONDITIONS OF LOW GAS FLOW AND LOW AMBIENT TEMPERATURES. 2) INSTALLATION OF ADDITIONAL PRESSURE TRANSMITTER TO DETECT FLOW THROUGH THE MASTER FUEL METER RELIEVE VALVE AND GENERATE A SYSTEM ALARM WHEN THE PRESSURE APPROACHES THE RELIEF VALVE SET POINT. THIS WILL PROMPT A CALL-OUT TO STATION PERSONNEL.