MARITIMES & NORTHEAST PIPELINE, L.L.C. (SPECTRA ENERGY PARTNERS, LP)

Incident Narrative

AT APPROXIMATELY 11:51 AM ET ON JUNE 15, 2021 MNE'S ELIOT COMPRESSOR STATION ESD SYSTEM WAS INADVERTENTLY ACTIVATED. THE APPARENT CAUSE OF THE ESD WAS IMPROPER INSTALLATION OF TUBING WHICH DISENGAGED FROM ITS TERMINATION POINT. THE TUBING WAS UNDER PIPELINE PRESSURE AT THE TIME AND RESULTED IN A DROP IN SUPPLY POWER GAS PRESSURE WHICH TRIGGERED THE ESD. THE RELEASE WAS DUE TO A SINGLE STATION ESD VALVE MOVING OUT OF SEQUENCE WITH THE OTHER FOUR (4) ESD SYSTEM VALVES. THE OUT OF SEQUENCE ESD VALVE WAS INADVERTENTLY LEFT CONNECTED TO THE PREVIOUS POWER GAS SYSTEM, WHICH ALLOWED IT TO MOVE WHILE THE OTHER ESD VALVES DID NOT. THE REMAINING FOUR (4) ESD VALVES THAT DID NOT MOVE WERE CORRECTLY CONNECTED TO THE NEW POWER GAS SYSTEM INSTALLED IN 2020. THE NEW ESD SYSTEM HAS BEEN TESTED TWICE SINCE INSTALLATION, AND THE ISSUE WAS NOT MADE EVIDENT IN THE TESTS. CORRECTIVE ACTION HAS BEEN TAKEN, AND THE SYSTEM WILL BE RETESTED BEFORE BEING PUT BACK INTO SERVICE. VERIFICATION OF TUBING CONNECTIONS AND POWER GAS SYSTEM WILL BE CONDUCTED BEFORE RETURNING TO SERVICE AS WELL. DUE TO THE INCORRECT POWER GAS SUPPLY, THE ESD BLOW OFF VALVE FAILED TO THE OPEN POSITION WHILE THE MAINLINE TAP VALVES REMAINED IN THE OPEN POSITION. AS A RESULT, THE STATION WAS NOT ISOLATED FROM THE MAINLINE WHICH RESULTED IN THE STATION BLOWDOWN VENTING GAS FOR APPROXIMATELY 8 MINUTES. MNE'S FIELD PERSONNEL SUBSEQUENTLY CLOSED THE MAINLINE TAP VALVES AFTER RECOGNIZING THAT THE MAINLINE TAP VALVES REMAINED IN THE OPEN POSITION. A NEARBY SCHOOL NOTIFIED FIRST RESPONDERS AND WAS SUBSEQUENTLY EVACUATED AS A PRECAUTION. AN ADDITIONAL NEARBY SCHOOL RELEASED THEIR FACULTY. AT THE TIME OF THE ESD, THE PRELIMINARY GAS LOSS WAS INITIALLY ESTIMATED TO BE LESS THAN THE DOT REPORTING THRESHOLD, SINCE A NORMAL ESD AT THIS LOCATION IS LESS THAN THE REPORTING THRESHOLD. SHORTLY BEFORE 6 PM EST ON JUNE 16, 2021 MNE CONFIRMED THAT THE GAS LOSS WOULD EXCEED THE DOT REPORTING THRESHOLD AND SUBSEQUENTLY NOTIFIED THE NRC AT APPROXIMATELY 7:21 PM EST ON JUNE 16, 2021. THE DELAY WAS DUE TO RECONFIRMATION THAT THE INCIDENT MET THE DOT REPORTING THRESHOLD. 08/12/2021 SUPPLEMENTAL REPORT CHANGES - UPDATED PART A4 TO MATCH PART A13 - ADDED ESTIMATED COST FOR PART D7C - REVISED PART G7 TO REFLECT INCORRECT OPERATION - UPDATED PART H TO INDICATE GAS LOSS WAS UNDERESTIMATED