ANR PIPELINE CO

Incident Narrative

ON THE MORNING OF APRIL 15, 2014, THE STATION TECHNICIAN ARRIVED AT GOODMAN COMPRESSOR STATION TO FIND GAS VENTING FROM THE STATION BLOWDOWN SILENCER. UPON FURTHER INVESTIGATION IT WAS FOUND THAT THE 8-INCH SUCTION BLOWDOWN VALVE WAS OPEN WITH NO ALARM OR SHUTDOWN INDICATION. THE 8"" SUCTION BLOWDOWN VALVE VENTED THE GAS INTO THE STATION BLOWDOWN SILENCER, WHICH LIMITS NOISE AND RESTRICTS FLOW VOLUME. IN ADDITION, THE STATION SUCTION AND DISCHARGE VALVES REMAINED OPEN, AS THE STATION HAD NOT SHUT IN. THE STATION TECHNICIAN IMMEDIATELY SHUT IN THE STATION, WHICH WAS NOT OPERATING AT THE TIME, AND ISOLATED IT FROM THE PIPELINE BY CLOSING THE STATION SUCTION AND DISCHARGE VALVES. GAS CONTROL WAS THEN NOTIFIED OF THE SITUATION. INVESTIGATION FOUND THAT THE STATION SUCTION BLOWDOWN VALVE PNEUMATIC PILOT PRESSURE SWITCH HAD ACTIVATED BECAUSE WATER HAD ACCUMULATED AND FROZE IN THE SWITCH AND PILOT GAS SENSING LINES RESULTING IN A LOSS OF PRESSURE TO THE SWITCH. THE LOSS OF PILOT GAS CAUSED THE PILOT PRESSURE SWITCH TO CHANGE STATE AND TO PNEUMATICALLY COMMAND THE BLOWDOWN VALVE TO ITS FAILSAFE POSITION, WHICH IS OPEN. LIQUIDS AND ICE WERE REMOVED FROM THE AFFECTED TUBING AND SWITCH, AS WELL AS FROM SIMILAR COMPONENTS ELSEWHERE AT THE STATION, THE AFFECTED BLOWDOWN VALVE WAS TESTED, AND STATION WAS PLACED BACK INTO SERVICE THE FOLLOWING WEEK. RECOMMENDATIONS HAVE BEEN MADE TO MODIFY THE TUBING TO THE AFFECTED SWITCHES TO ELIMINATE THE ACCUMULATION OF LIQUIDS. IN ADDITION, IT HAS BEEN RECOMMENDED TO MODIFY STATION CONTROL LOGIC TO SHUT DOWN THE STATION AND CLOSE THE STATION SUCTION AND DISCHARGE VALVES WHEN ANY BLOWDOWN VALVE INDICATES OPEN AND TO ANNUNCIATE AN ALARM TO GAS CONTROL.