COLUMBIA GAS TRANSMISSION, LLC

Incident Narrative

ON THE EVENING OF NOVEMBER 11TH, 2020, STORAGE FIELD (SF) PERSONNEL FROM COLUMBIA GAS TRANSMISSION, LLC (COMPANY), A TC ENERGY ENTITY, RESPONDED TO AN EVENT AT DONEGAL STORAGE FIELD WHICH IS OPERATED AND MAINTAINED BY THE COMPANY. AT 9:33 PM, COMPANY MONITORING CENTER PERSONNEL RECEIVED A CALL FROM GAS CONTROL REGARDING A PRESSURE DROP. THE PRESSURE HAD DROPPED FROM 1,190 TO 1,156 PSIG, FOLLOWED BY A SUBSEQUENT DROP TO 1,035 PSIG AFTER SHUTTING-IN PRESSURE REGULATION. AT 9:35 PM, FIELD PERSONNEL WERE CONTACTED BY A NEAR-BY PROPERTY OWNER REPORTING THE SOUND OF A GAS LINE LEAK; SUBSEQUENTLY, COMPANY OPERATIONS PERSONNEL WERE NOTIFIED TO RESPOND TO THE EVENT LOCATION. FIRST RESPONDER ARRIVED ON SCENE AT 9:45 PM AND OBSERVED GAS BLOWING; THE LOCAL FIRE DEPARTMENT CLOSED CUNNINGHAM ROAD AT THIS TIME. AT 9:54 PM A COMPANY SF TECHNICIAN CONFIRMED THAT THE REPORTED LEAK HAD BEEN ISOLATED BY OPERATING THE CRITICAL VALVE. THE NATIONAL RESPONSE CENTER (NRC) AND PHMSA ACCIDENT INCIDENT DIVISION WERE CONTACTED WITHIN 1 HOUR OF CONFIRMED DISCOVERY AT 10:50 PM. NRC ONE-HOUR (1291972) AND 48-HR (1292099) REPORTS WERE COMPLETED ON NOVEMBER 11TH AND NOVEMBER 13TH RESPECTIVELY. THE FAILED STORAGE LINE (9190) WAS SECURED AND SENT TO A METALLURGICAL FAILURE ANALYSIS LABORATORY TO EVALUATE AND DETERMINE THE PROBABLE CAUSE BEHIND THIS PIPELINE FAILURE. THE REPAIR OF THE LINE CONSISTED OF PIPE REPLACEMENT. THE METALLURGICAL ROOT CAUSE OF THE FAILURE WAS DUE TO EXTERNAL CORROSION IDENTIFIED ALONG THE 6:00 O'CLOCK ORIENTATION OF THE PIPE. THE ABSENCE OF AN EXTERNAL COATING AND EXPOSURE TO ATMOSPHERE (I.E. DE-COUPLED FROM THE SOIL ELECTROLYTE) WERE CONTRIBUTING FACTORS TO THE CORROSION OF THE PIPE. IN AN EFFORT TO PREVENT FUTURE OCCURRENCE, THE COMPANY HAS LOOKED BEYOND THIS LOCATION TO OTHER SEGMENTS WITH SIMILAR ENVIRONMENTAL CONDITIONS AND PIPE CHARACTERISTICS WHERE CORROSION MAY ADVERSELY IMPACT LINE INTEGRITY; TO THAT END, TWO OPPORTUNITIES FOR MITIGATIVE MEASURES HAVE BEEN SCHEDULED FOR COMPLETION BEFORE DECEMBER 31, 2022. THE PROJECTS WILL INVOLVE REPLACING LINE SEGMENTS AND ASSESSMENT OF THE REMOVED SEGMENTS FOR EXTERNAL CORROSION. NOTE: ALL TIMES WERE RECORDED IN EASTERN STANDARD TIME