MIDCONTINENT EXPRESS PIPELINE LLC

Incident Narrative

ON 06/27/2023 AT 12:00 PM, MIDCONTINENT EXPRESS PIPELINE (MEP) HAD A REPORTABLE GAS RELEASE THAT OCCURRED AT THE MEP 2 COMPRESSOR STATION WHEN THE ESD SYSTEM WAS ACTIVATED AND THE DISCHARGE SIDE OF THE ESD SYSTEM DID NOT OPERATE AS DESIGNED. THE ESD WAS ACTIVATED AS A RESULT OF LOSS OF UPS POWER SUPPLY. THE USE OF THE UPS POWER WAS INITIATED BY A TRIPPED ELECTRICAL BREAKER THAT WAS CAUSED BY AN ELECTRICALLY SHORTED AIR COMPRESSOR. THE ESD BLOCK VALVE THAT IS HELD CLOSED BY AN ENERGIZED SOLENOID, WHEN SUPPLIED BY COMMERCIAL OR UPS POWER. WHEN UPS BATTERIES WERE DRAINED, THE STATION LOST CONTROL POWER TO THE STATION COMPUTERS, PLCS AND UNIT HMIS. THE LOSS OF COMMERCIAL POWER DUE TO TRIPPED BREAKER AND THE LOSS OF UPS POWER ALLOWED THE ESD VALVE TO OPEN CAUSING THE STATION TO BLOWDOWN THROUGH A FULLY PNEUMATIC SYSTEM. WHEN RESPONSE PERSONNEL ARRIVED THEY FOUND THE STATION DISCHARGE SIDE GATE AND DISCHARGE BLOWDOWN VENT VALVE IN AN OPEN POSITION WHICH LED TO THE 50,086.93 MCF RELEASE OF NATURAL GAS. THE ESD SYSTEM BY DESIGN HAS AN INTERLOCK PROCESS SO THAT THE BLOWDOWN VALVES WILL NOT OPEN UNLESS THE ASSOCIATED STATION SIDE GATE VALVES CLOSE. THIS IS ACCOMPLISHED THROUGH A SERIES OF TRIGGER VALVES. THE SUCTION SIDE OF THE STATION WORKED AS DESIGNED DURING THE ESD. HOWEVER, THE DISCHARGE SIDE EXPERIENCED FAILURES IN TWO SHAFER TRIGGER VALVES WHICH ALLOWED THE BLOWDOWN VENT VALVE TO OPEN WITH THE DISCHARGE SIDE GATE OPEN. THE INVESTIGATION FOUND EXCESSIVE CORROSION/RUST WITHIN THE INTERNAL WORKINGS OF THE TWO SHAFER VALVES. THE SHAFER TRIGGER VALVES WERE REPLACED, THE TRIPPED BREAKER WAS RESET, THE SHORTED AIR COMPRESSOR WAS REMOVED FROM SERVICE UNTIL THE MOTOR WAS REPLACED, THE DISCHARGE SIDE GATE AND EDS DISCHARGE BLOWDOWN VALVE WERE RETURN TO THEIR NORMAL STATE AND THE STATION WAS PLACED BACK ONLINE.