TENNESSEE GAS PIPELINE COMPANY

Incident Narrative

ON JULY 23, 2021, AT 23:06, TENNESSEE GAS PIPELINE COMPANY (TGP) GAS CONTROL BEGAN TO OBSERVE INDICATIONS OF DECREASING DISCHARGE PRESSURE READINGS FROM 758 PSIG TO 666 PSIG AT COMPRESSOR STATION 114. TGP GAS CONTROLLER CALLED THE FIELD OPERATOR TO GO OUT AND ASSESS THE PRESSURE CHANGES. FIELD OPERATOR ARRIVED AT 00:10, SAFELY ENTERED THE STATION, AND BEGAN THE INVESTIGATION. FIELD OPERATOR FOUND ESD VALVE BDS-2 IN THE OPEN POSITION RELEASING NATURAL GAS TO ATMOSPHERE. IMMEDIATELY THE FIELD OPERATOR ATTEMPTED TO CLOSE VALVE BDS-2 WITHOUT SUCCESS AND SUBSEQUENTLY BEGAN CLOSING AN ADJACENT MANUAL ISOLATION VALVE TO SUCCESSFULLY STOP THE RELEASE OF GAS. FIELD OPERATOR ISOLATED VALVE BDS-2 WITHOUT AFFECTING NORMAL OPERATIONS. ROOT CAUSE INVESTIGATION FOUND A FAILED O-RING IN THE PILOT CHAMBER SERVING THE BIFFI VALVE OPERATOR ON VALVE BDS-2. THE FAILED O-RING ALLOWED REVERSING GAS TO ENTER THE POWER SIDE OF THE CONTROLLER THEREBY UNINTENTIONALLY OPENING VALVE BDS-2, RELEASING GAS TO ATMOSPHERE. IN ORDER TO PREVENT RECURRENCE TGP STAFF DISCUSSED THE O-RING FAILURE INVESTIGATION WITH THE PILOT VENDOR. THE VENDOR SUGGESTED INSTALLING A CHECK VALVE AT THE VALVE PILOT TO PREVENT UNINTENTIONAL REVERSING GAS PRESSURE IN THE EVENT OF AN O-RING FAILURE. ALSO KNOWING THAT COMPRESSOR STATION 114 HAD SIMILAR STATION PILOT VALVES INSTALLED AT THE STATION, TGP STAFF WILL BE ASSESSING THE OTHER PILOT VALVES AND WILL INSTALL CHECK VALVES AS APPLICABLE. TGP STAFF WILL MODIFY THE STATION'S ESD SYSTEM TESTING PROCEDURE TO INCLUDE REVERSING GAS SUPPLY VALVES AND FUNCTIONALITY AND WILL REVIEW STATION CONTROLS AND ALARMS WITH CONSIDERATION OF APPROPRIATE CALL-OUT STATUS FOR OPEN VENT AND BLOWDOWN VALVES.