TRANSCOLORADO GAS TRANSMISSION COMPANY LLC

Incident Narrative

ON 10/26/2020 AT 18:25 LOCAL TIME, THE TRANS COLORADO GAS TRANSMISSION COMPANY LLC (TCP)- MANCOS COMPRESSOR STATION EXPERIENCED AN UNPLANNED ESD EVENT. UNIT 380 WAS ONLINE AT THE TIME OF THE ESD AND SHUT DOWN. WHEN THE LOCAL OPERATION'S TECHNICIAN ARRIVED ON SITE AT 19:12 LOCAL TIME THAT DAY, THE STATION COMPRESSOR UNIT NOS. 380 AND 381 WERE BOTH OBSERVED TO BE OFF-LINE AND BLOWN-DOWN AS DESIGNED BY THE STATION AUTOMATION SYSTEM. THE ON-SITE GENERATOR UNIT 382 WITH FUEL SYSTEM WAS ALSO COMPLETELY BLOWN-DOWN. THE OPERATION'S TECHNICIAN ALSO CONFIRMED THE STATION YARD PIPING WAS FULLY BLOWN DOWN WITH THE SUCTION SIDE ESD VENT VALVE STUCK IN TRANSITION BETWEEN THE CLOSED AND OPEN POSITIONS. SIDE GATE VALVES WITH THE MAINLINE PIPE WERE IN THE CLOSED POSITION. THE TOTAL ESTIMATED GAS LOSS WAS 184 MSCF AND CALCULATED USING STATION PIPE VOLUME AND PRESSURE AND DETERMINED NOT TO BE A REPORTABLE EVENT SINCE A REPORTABLE QUANTITY HAD NOT BEEN EXCEEDED. WHILE INVESTIGATING THE IMMEDIATE CAUSE, THE OPERATION'S TECHNICIAN OBSERVED THE DISCHARGE SIDE ESD VENT VALVE IN THE CLOSED POSITION. THE EXPECTED POSITION OF THE ESD VENT VALVES AFTER A STATION ESD IS FULL OPEN. PER KINDER MORGAN PROCEDURES, A STATION ESD THAT RESULTS IN A RELEASE OF NATURAL GAS UNDER THE PHMSA REPORTING THRESHOLD FOR NATURAL GAS MUST BE INVESTIGATED AS AN ABNORMAL OPERATION. THE INITIAL INVESTIGATION FOUND ICE PRESENT IN THE PNEUMATIC SYSTEM THAT CONTROLS THE STATIONS TWO MAIN ESD VENT VALVES. OPERATIONS DECIDED TO LEAVE THE STATION DOWN AND RESUME THE INVESTIGATION THE FOLLOWING DAY SINCE THE AMBIENT TEMPERATURES WERE BELOW FREEZING AND IT WAS BECOMING TOO DARK TO WORK SAFELY. ADDITIONAL INVESTIGATION ON 10/27/2020 REVEALED THAT THE SUCTION SIDE ESD VENT VALVE OPENED PRIOR TO THE ESD AT 16:59:08 ON 10/26/2020, ABOUT 86 MINUTES PRIOR TO THE ESD EVENT. BASED ON THIS INFORMATION, AT 12:45 LOCAL TIME, IT WAS DETERMINED THAT GAS LOSS VOLUMES EXCEEDED THE REPORTABLE THRESHOLD OF 3,000 MSCF. AT 13:05 LOCAL TIME ON 10/27/2020, CONFIRMATION OF DISCOVERY THAT A REPORTABLE INCIDENT WAS IMMEDIATELY REPORTED TO THE NRC AT 13:43 LOCAL TIME. THE INVESTIGATION TEAM CONCLUDED THAT THE BUILDUP OF WATER OVER TIME FROZE AND BLOCKED THE SUPPLY OF AIR TO THE SUCTION-ESD BLOWDOWN VENT VALVE OPERATOR, THEREBY REDUCING THE PRESSURE REQUIRED TO KEEP THE SUCTION-ESD VENT VALVE SHUT AND ALLOWING IT TO OPEN SLOWLY AND RELEASE GAS. ONCE THE SUCTION-ESD VALVE OPENED FAR ENOUGH, IT ACTIVATED THE ""OPEN"" LIMIT SWITCH ON THE SUCTION-ESD BLOWDOWN VALVE AND ALONG WITH SENSING FLOW WITHIN THE ESD VENT PIPING RESULTING IN A FULL STATION ESD. THE ROOT CAUSE OF THE EVENT WAS DETERMINED TO BE FAILURE TO REALIZE THAT END-POINT DEVICES ON A DRIED AIR SYSTEM STILL REQUIRE PERIODIC PURGING/DRAINING TO PREVENT ACCUMULATION OF WATER OVER EXTENDED PERIODS OF TIME. TCP IS WORKING TO IMPLEMENT ADDITIONAL MAINTENANCE PROCEDURES FOR REGULAR PURGING AND DRAINING OF ESD PIPING/ENDPOINT DEVICES ON INSTRUMENT AIR SYSTEMS AND ENTER THEM INTO OUR OPERATION\MAINTENANCE WORK-TRACKING SYSTEM. TCP PLANS TO EVALUATE OTHER STATIONS ON THE TCP SYSTEM TO DETERMINE IF PURGING AND DRAINING MAINTENANCE OF ESD PIPING/ENDPOINT DEVICES IS REQUIRED TO MINIMIZE THE POTENTIAL FOR A REOCCURRENCE OF THIS TYPE OF EVENT.