SCM OPERATIONS, LLC

Incident Narrative

THE RELEASE OF NGL VAPORS OCCURRED ON THE MORNING OF SEPTEMBER 21, 2023, AS A RESULT OF A PACKING FAILURE ON THE VALVE STEM OF A 24"" GATE VALVE ON SCM OPERATIONS, LLC'S (SCM) NGL TRANSMISSION SYSTEM IN REEVES COUNTY, TEXAS. THE EVENT OCCURRED AFTER SCM'S DOWNSTREAM CUSTOMER (ENTERPRISE) EXPERIENCED A LIGHTNING STRIKE THAT CAUSED THEIR VALVE AT THE RECEIPT SITE TO FAIL CLOSED, WHICH CAUSED SCM'S 24"" DELIVERY VALVE TO CLOSE ON HIGH DIFFERENTIAL. SCM'S LINE PRESSURE REACHED 1,327 PSIG, WHICH IS BELOW THE MAOP OF THE SYSTEM OF 1,480 PSIG. WHEN ENTERPRISE WAS ABLE TO RESET THEIR SYSTEM, SCM'S DELIVERY VALVE (MOV 0312) WAS THEN OPENED BY SCM'S CONTROL ROOM. THE VALVE OPENING REQUIRED 4 ITERATIONS OF THE OPEN/CLOSE ACTION OVER THE COURSE OF A 17-MINUTE TIME PERIOD. WHILE THE VALVE WAS BEING OPENED, ENTERPRISE'S ON-SITE TECHNICIAN HEARD A LOUD POP, OBSERVED A LEAK, AND CONTACTED SCM. SCM PERSONNEL MOBILIZED TO SITE AND INSTRUCTED THE CONTROL ROOM TO ISOLATE THE LINE SEGMENT BY CLOSING AN ISOLATION VALVE AT THE UPSTREAM VALVE SETTING. UPON ARRIVAL ON SITE SCM PERSONNEL CONFIRMED DISCOVERY OF A LEAK ON VALVE MOV 0312, AND DETERMINED A BLOWDOWN OF THE LINE WAS NECESSARY TO EFFECTUATE REPAIRS. THE BLOWDOWN WAS INITIATED, AND THE PRESSURE WAS DRAWN DOWN BY THE FOLLOWING MORNING. A VALVE REPAIR TEAM INSPECTED THE FAILED VALVE AND DETERMINED A REPLACEMENT WAS NECESSARY. A REPLACEMENT VALVE WAS INSTALLED, AND THE LINE SEGMENT WAS PLACED BACK INTO SERVICE ON SEPTEMBER 24, 2023. FOLLOWING THE REMOVAL AND DISASSEMBLY OF THE FAILED VALVE AN INSPECTION REVEALED THE SEAL BETWEEN THE GRAPHITE PACKING AND THE VALVE STEM WAS COMPROMISED DUE TO WEAR ON THE PACKING AND ROUGHNESS OF THE VALVE STEM. THE LEAK OCCURRED WHEN THE COMPROMISED SEAL WAS BREACHED AFTER THE MULTIPLE CYCLING ATTEMPTS TO OPEN THE VALVE. DURING THE CYCLE ATTEMPTS THE EXPANDING NGL WOULD HAVE COOLED AN ESTIMATED 0.1 DEG F WITH A DIFFERENTIAL PRESSURE OF 50 PSID. BASED ON THE ROUGHNESS OF THE STEM, THE REDUCED FRICTION BETWEEN THE STEM AND THE PACKING, RAPID PRESSURIZATION OF THE BODY CAVITY, AND INSUFFICIENT TIME FOR TEMPERATURE TO EQUALIZE, NGL LIKELY MIGRATED INTO THE PACKING GLAND UNTIL THE PIPELINE PRESSURE OF APPROXIMATELY 1,327 PSIG OVERCAME THE ABILITY OF THE PACKING TO MAINTAIN A SEAL. VALVE STEM ROUGHNESS MAY HAVE BEEN A CONTRIBUTING FACTOR TO THE WEAR ON THE PACKING, SO THE VALVE STEM MATERIAL WAS EVALUATED. IT WAS IDENTIFIED TO BE AISI 4140, WHICH IS A LOW ALLOY STEEL AND OFTEN SELECTED FOR ITS TOUGHNESS AND HIGH FATIGUE STRENGTH, HOWEVER, IT HAS A HIGHER CARBON CONTENT THAN A182 F6A OR 17-4. ALTHOUGH AISI 4140 IS WITHIN INDUSTRY STANDARDS, AN UPGRADE ON THE VALVE STEM MATERIAL TO AISI 4140 WITH 3 MILS OF ELECTROLESS NICKEL PLATING (ENP), A182 F6A, OR 17-4 IS A POSSIBLE DESIGN IMPROVEMENT THAT COULD LOWER THE RISK OF A SIMILAR FAILURE. PLAN TO PREVENT RECURRENCE REVIEW OF THE ISOLATION VALVES ON SCM'S SYSTEM IDENTIFIED ONE OTHER VALVE WITH A STEM THAT WAS OF SIMILAR MATERIAL. THE STEM CANNOT BE VISUALLY EXAMINED DURING NORMAL VALVE MAINTENANCE AND INSPECTION, THEREFORE, SCM WILL REPLACE THAT VALVE WITH ONE THAT HAS A STEM WITH IMPROVED METALLURGICAL PROPERTIES.