SOUTHERN STAR CENTRAL GAS PIPELINE, INC

Incident Narrative

ON 12/11/2015 AT 09:56 AM SSC GAS CONTROL RECEIVED PHONE CALL FROM A SUPERIOR CASHION EMPLOYEE STATING THAT THE RELIEF VALVE ON THE SSC CASHION SETTING WAS RELEASING GAS. WHILE ON THE PHONE SSC GAS CONTROL ISSUED A ZERO SET POINT AT THE FLOW CONTROL FOR THE SSC CASHION SETTING AND THE RELEASE OF GAS WAS CONFIRMED TO BE STOPPED AT 09:57. AT 09:58 SSC GAS CONTROL NOTIFIED PSAP THAT A RELIEF VALVE HAD BEEN GOING OFF IN THE AREA BUT HAD BEEN CONFIRMED TO HAVE STOPPED. SSC GAS CONTROL NOTIFIED SSC OPERATIONS AT 09:58 TO TRAVEL TO THE SITE TO INVESTIGATE THE ISSUE. SSC OPERATIONS ARRIVED ON SITE AT 12:12, AFTER INITIAL TESTING THE RELIEF VALVE ACTIVATED DURING TEST AT SET PRESSURE AND RESEATED PROPERLY. NO ISSUES WERE FOUND WITH THE RELIEF VALVE. SSC GAS CONTROL REVIEWED FLOWS OF THE SETTING AND IT WAS DISCOVERED THAT THE METER BEGAN SHOWING NO FLOW AT APPROXIMATELY 15:00 ON 12/10/15. BEFORE THAT POINT THE METER WAS RECEIVING BETWEEN 5-6 MMCF/DAY RATE. AFTER DISCUSSING THIS WITH SUPERIOR CASHION, THEY STATED THEY HAD NOT SHUT DOWN THEIR FLOWS. AT THE TIME WHEN THE FLOW WENT TO 0 THE PRESSURE ON THE SEGMENT WAS AT 360 PSIG, 53 POUNDS UNDER MAOP, AND THEN DROPPED AND SETTLED AT 343 PSIG. IT IS BELIEVED THAT THE RELIEF VALVE BEGAN RELIEVING AT 14:50 ON 12/10/2015 AND CONTINUED TO BLOW UNTIL THE NEXT MORNING WHEN SSC RECEIVED A CALL. THE PRESSURE SHOWED A STABILIZATION BECAUSE THERE IS A CHECK VALVE BETWEEN THE RELIEF AND THE METER SETTING AND THE CLOSURE OF THIS VALVE TO PREVENT BLOWING DOWN THE SSC MAINLINE WOULD CAUSE THE METER SETTING TO MEASURE THE SAME PRESSURE AS THE MAINLINE WITH 0 FLOW. SSC CONTACTED THE CUSTOMER AND DETERMINED THERE WAS A PERIOD WHEN THEY HAD DELIVERED HIGHER PRESSURE GAS. ONCE THE HIGH PRESSURE GAS SLUG REACHED THE RELIEF VALVE IT ACTIVATED. THE RELIEF VALVE ACTIVATED AS INTENDED, BUT SSC WAS NOT ABLE TO SEE THE GAS RELEASE DUE TO THE CLOSURE OF THE CHECK VALVE. BECAUSE THE CUSTOMER HAD REACHED NOMINATION FOR THE DAY GAS CONTROL DID NOT SEE ANY ISSUE WITH THE METER READING 0 FLOW (NO FLOW). SSC HAS INSTALLED A NEW TRANSMITTER FOR THE METER SETTING UPSTREAM OF THE RELIEF VALVE TO DETERMINE A DIFFERENCE IN PRESSURE ON EITHER SIDE OF THE CHECK VALVE IF CLOSED AND AID IN THE NOTIFICATION OF RELIEVING GAS IN THE FUTURE.