SOUTHERN STAR CENTRAL GAS PIPELINE, INC

Incident Narrative

ON 3/20/2020 AT 8:02 PM MDT, SOUTHERN STAR CENTRAL GAS PIPELINE (SSCGP) GAS CONTROL RECEIVED A CALL FROM A NOBLE KEOTA EMPLOYEE ABOUT NOISE COMING FROM THE INTERCONNECT METER FACILITY. SSCGP EMPLOYEE ARRIVED ON SITE AT 9:33 PM AND CONFIRMED THE RELIEF VALVE WAS VENTING. AFTER CONFIRMING THERE WAS NO OVERPRESSURE EVENT THE RELIEF VALVE WAS ISOLATED AT 9:42 PM. THE RELIEF VALVE WAS INSPECTED AND TESTED, IT WAS FOUND THAT THE SET POINT HAD DRIFTED TO 954 PSIG. THE TEMPERATURE AT THE TIME OF THE RELEASE WAS 16 DEGREES F. THE SET POINT WAS ADJUSTED BACK TO 988 PSIG. GAS LOSS WAS CALCULATED AT 10:11 PM AT 3.9 MMCF. THE NRC WAS NOTIFIED AT 10:47 PM. THE RELIEF VALVE WAS PLACED BACK IN SERVICE BY 11:00 PM. IN RESPONSE TO QUESTIONS SUBMITTED BY PHMSA, THE FOLLOWING RESPONSES ARE INCLUDED IN THIS SUPPLEMENTAL REPORT: Q: DID DEBRIS CONTRIBUTE TO THE FAILURE? A: WHEN THE PRESSURE RELIEF VALVE (PRV) WAS INSPECTED AFTER THE RELEASE NO DEBRIS WAS FOUND INSIDE OF THE PRV. THE AS FOUND SET POINT MATCHED THE PRESSURE ACHIEVED (954 PSI) SO THE PRV RELEASED AS SET. Q: HAS THE SET POINT DRIFTED BEFORE? A: THIS PRV RECEIVED ITS LAST ANNUAL INSPECTION ON 8/27/2019 AND THE AS FOUND SET POINT WAS 986 PSI. THE SET POINT WAS READJUSTED TO 988 AT THAT TIME. AT THE TIME, THE 2 PSI DRIFT WAS NOT CONSIDERED ENOUGH FOR CONCERN. Q: WHAT PREVENTATIVE MEASURES ARE BEING TAKEN TO PREVENT THIS IN THE FUTURE? A: THE PRV AT THIS RECEIPT POINT IS SPRING CONTROLLED. THROUGH OUR RESEARCH OF MANUFACTURE INFORMATION AND DISCUSSION WITH OPERATIONS, THE SPRING CONTROLLED PRVS SEEM TO BE MORE SUBJECT TO DRIFTING OF SET POINT AND RESEATING PRESSURES DURING RAPID PRESSURE FLUCTUATIONS AND LOW TEMPERATURES. IN THIS CASE THE VALVE DID NOT RESEAT UNTIL ALL PRESSURE WAS RELIEVED WHEN IT WAS ISOLATED. WE ARE SCOPING A PROJECT TO REPLACE THIS SPRING CONTROLLED PRV WITH A PILOT CONTROLLED PRV. WE ARE LOOKING AT ALL OF OUR RECEIPT POINTS WITH SIMILAR CONFIGURATIONS AND PRIORITIZING REPLACEMENT PROJECTS FOR THOSE ALSO.