EL PASO NATURAL GAS CO

Incident Narrative

KEYSTONE COMPRESSOR STATION WAS REMOVED FROM SERVICE FOR SCHEDULED ANNUAL CHECKS AND MAINTENANCE AT 8:00 AM. APPROXIMATELY 45 MINUTES AFTER THE STATION WAS OFF-LINE, THE PLANT B INLET SUCTION PIPING RELIEF VALVE (SET AT 580 PSIG) BEGAN RELIEVING PRESSURE INTERMITTENTLY. GAS CONTROL WAS NOTIFIED AT 9:40 AM. GAS CONTROL STATED THAT A SECOND UNIT HAD BEEN PLACED IN SERVICE TO MOVE GAS VOLUME OUT OF THE PERMIAN WHICH HELPED REDUCE THE PRESSURE AT THE KEYSTONE COMPRESSOR STATION. THE RELIEF VALVE CONTINUED TO RELIEVE PRESSURE INTERMITTENTLY AND AT THAT POINT GAS CONTROL WAS NOTIFIED AND THEY VERIFIED THROUGH SCADA SYSTEM THAT THE PRESSURE HAD CONTINUED TO DECREASE. ON SITE OPERATION PERSONNEL RESPONDED TO THE RELIEF VALVE AND VERIFIED THAT A MANUAL PRESSURE GAUGE NEAR THE RELIEF VALVE WAS SHOWING INCORRECT PRESSURE OF 580 PSIG WHEN COMPARED TO PRESSURE FROM GAS CONTROL. THE GAUGE WAS REMOVED AND REPLACED WITH A DIFFERENT ONE THAT INDICATED A PRESSURE OF 522 PSIG WHICH WAS CONFIRMED WITH WHAT GAS CONTROL WAS SEEING. OPERATIONS THEN ISOLATED THE RELIEF VALVE. INSPECTION OF THE RELIEF VALVE REVEALED THAT ITS SEAL WAS BROKEN AND LOCKING MECHANISM HAD BACKED OUT CAUSING IT TO RELIEVE AT PRESSURES LOWER THAN ITS NORMAL SET PRESSURE. THE MAINTENANCE CONTRACTOR SUCCESSFULLY CALIBRATED AND RESET THE RELIEF VALVE BY TESTING IT THREE (3) TIMES TO RELIEVE AT 580 PSIG. THE RELIEF VALVE WAS RESEALED AND RETURNED TO SERVICE.