KANSAS GAS SERVICE

Incident Narrative

ON 8/2/11, THE VENT VALVE ON THE CALISTA COMPRESSOR STATION UNIT NUMBER 2 INADVERTENTLY OPENED WHEN THE UNIT WAS SHUT DOWN BY GAS CONTROL AT 22:10 HOURS. THE VENT VALVE (DESIGNATED G1-025) IS A 2-INCH ANSI 300 PLUG VALVE WITH A SHAFER AIR-OVER-HYDRAULICS ACTUATOR. THE VALVE IS USED TO BLOW DOWN COMPRESSOR UNIT PIPING FOR MAINTENANCE PURPOSES. THE GAS CONTROL ROOM RECEIVED ALARMS AFTER SHUTDOWN FROM THEIR SUPERVISORY CONTROL AND DATA ACQUISITION (SCADA) SYSTEM ABOUT THE OPEN VENT VALVE BUT THE GAS CONTROLLER DID NOT MAKE ANY NOTIFICATION TO FIELD PERSONNEL OR MANAGEMENT. GAS VENTED THROUGH THE VENT VALVE AT APPROXIMATELY 420 PSIG LINE PRESSURE UNTIL COMPANY CREWS ARRIVED AT THE STATION THE NEXT MORNING AND HEARD THE GAS VENTING AND CLOSED THE VENT VALVE. TECHNICIANS UNSUCCESSFULLY TRIED TO REPLICATE THE VALVE FAILURE BY STARTING AND STOPPING THE COMPRESSOR UNIT NUMBER 2, BUT THE VALVE NEVER OPENED. THE EXACT CAUSE OF THE EQUIPMENT FAILURE IS UNKNOWN. ALL VALVES UTILIZING THE AIR-OVER-HYDRAULIC ACTUATORS WERE REMOVED TO PREVENT REOCCURRENCE OF THIS SITUATION. ALTHOUGH EQUIPMENT FAILURE WAS DETERMINED TO BE THE ROOT CAUSE OF THE INCIDENT, IF THE GAS CONTROLLER HAD NOTIFIED FIELD PERSONNEL IN A TIMELY MANNER, THE AMOUNT OF GAS RELEASED WOULD HAVE BEEN LESS THAN THE 3,000 MCF REPORTING THRESHOLD.