INTERIOR GAS UTILITY

Incident Narrative

THE INTERIOR GAS UTILITY (IGU) LNG STORAGE AND VAPORIZATION SITE NUMBER 3 (SS3) IN FAIRBANKS, ALASKA SENT COLD GAS AND POSSIBLY LNG TO THE DISTRIBUTION SYSTEM. WHEN THE COLD GAS OR LNG ENTERED THE DISTRIBUTION SYSTEM, IT EMBRITTLED THE 8' UNDERGROUND HDPE PIPE, WHICH SUBSEQUENTLY RUPTURED IN A SECTION OF PIPING WITHIN IGU PROPERTY. THE HIGHEST RECORDED PRESSURE DOWNSTREAM OF THE DISTRIBUTION REGULATORS AT SS3 WAS 62PSIG. AT APPROXIMATELY 4:10PM ON 11/21/2021, A TEMPERATURE SWITCH ON THE OUTLET OF THE VAPORIZER MALFUNCTIONED AND CLOSED A VALVE TO STOP THE FLOW OF LNG THROUGH THE VAPORIZER. WITH NO LNG TO VAPORIZE, THE GLYCOL HEATER TURNED OFF DUE TO LOW DEMAND. AT ABOUT 4:55PM, AN OPERATOR NOTICED THAT THE FLOW OF LNG HAD STOPPED, AND THE DISTRIBUTION PRESSURE WAS DROPPING. THE OPERATOR OPENED THE CLOSED VAPORIZER VALVE VIA REMOTE CONTROL. THE OPERATOR DID NOT NOTICE THAT THE BOILER WAS NOT FIRING AND DID NOT MONITOR THE SITE LONG ENOUGH TO VERIFY THE SYSTEM WAS STABLE AND PROPER TEMPERATURES WHERE BEING MAINTAINED. DUE TO THE MALFUNCTIONING TEMPERATURE SWITCH AND A TEMPERATURE TRANSMITTER THAT HAD NOT BEEN PROGRAMMED TO ACT AS A BACKUP TO THE TEMPERATURE SWITCH, THE CONTROL SYSTEM DID NOT STOP THE FLOW OF LNG THROUGH THE VAPORIZER, UPON A LOW GAS TEMPERATURE ON THE OUTLET OF THE VAPORIZER. THE BOILER ATTEMPTED TO FIRE ABOUT THREE MINUTES AFTER THE LNG FLOW RESUMED BUT FAILED TO STAY RUNNING. THE SYSTEM ATTEMPTED TO START A BACK-UP BOILER ABOUT 10 MINUTES LATER, ABOUT WHEN THE DISTRIBUTION LINE RUPTURED. THE STANDARD OPERATING PROCEDURES WILL BE REVISED TO NO LONGER ALLOW CONTROL CHANGES FROM VIA REMOTE CONTROL (EXCEPT FOR EMERGENCY SHUT DOWNS AND SPECIFIED EXCEPTIONS) AND INSTEAD REQUIRE THE MONITORING OPERATOR TO TRAVEL TO THE SITE TO MAKE THE NECESSARY ADJUSTMENTS AND CHANGES. THE VAPORIZER TEMPERATURE SWITCHES WILL BE RECOMMISSIONED, AND THE TEMPERATURE TRANSMITTERS WILL BE ADDED INTO THE VAPORIZER SHUTDOWN PROGRAMMING LOGIC TO ADD REDUNDANCY. ADDITIONALLY, A DOWNSTREAM TEMPERATURE TRANSMITTER LOCATED ON THE METER SKID WILL BE USED TO SHUT DOWN THE LNG PUMPS IF LOW TEMPERATURE IS DETECTED INDICATING THE VAPORIZER SHUTDOWNS FAILED TO ACTIVATE AS A RESULT OF LOW OUTLET TEMPERATURE.