COLUMBIA GAS TRANSMISSION, LLC

Incident Narrative

ON JANUARY 29, 2020 WHILE CONDUCTING ROUTINE PIPELINE LEAK SURVEY, COMPANY PERSONNEL DETECTED THE PRESENCE OF NATURAL GAS IN A VENT ALONG A CASED ROAD-CROSSING ON LINE 1655 NEAR DILLSBURG, YORK COUNTY, PENNSYLVANIA. LINE 1655 IS A 10-INCH COATED CARBON STEEL TRANSMISSION PIPELINE WITH A MAXIMUM ALLOWABLE OPERATING PRESSURE OF 936 PSIG. THIS PIPELINE IS OPERATED AND MAINTAINED BY COLUMBIA GAS TRANSMISSION, LLC (COMPANY) A TC ENERGY ENTITY WITH THE OPERATOR ID 2616. NATURAL GAS SAMPLES WERE TAKEN FROM THE VENT PIPE AND A NEARBY METERING STATION ON LINE 1655, THEN SENT TO AN INDEPENDENT LABORATORY FOR ANALYSIS. RESULTS CONFIRMED THAT THE SOURCE OF NATURAL GAS WAS FROM PIPELINE 1655. A PRESSURE REDUCTION FROM 702 PSIG DOWN TO 600 PSIG WAS PUT IN PLACE TO MAINTAIN UNINTERRUPTED FLOW TO APPROXIMATELY 42,000 DOWNSTREAM CUSTOMERS THAT WERE SERVICED BY THE LOCAL DISTRIBUTION COMPANY. THE NATIONAL RESPONSE CENTER (NRC) AND PHMSA ACCIDENT INVESTIGATION DIVISION WERE NOTIFIED OF THE INCIDENT (NRC# 1269937). PIPELINE STOPPLES AND BYPASS PIPING WERE INSTALLED AROUND THE LEAK AREA TO MAINTAIN NATURAL GAS FLOW DOWNSTREAM WHILE REPLACING THE PIPELINE THROUGHOUT THE ROAD CROSSING AREA. THIS WORK REQUIRED THE CLOSURE OF STATE ROUTE (SR) 74 AND TRAFFIC MANAGEMENT AROUND THE AREA. EVIDENCE SECTION OF PIPE WAS SENT FOR METALLURGICAL ANALYSIS BY AN INDEPENDENT LABORATORY. ANALYSIS INDICATED STRAY CURRENT INDUCED EXTERNAL CORROSION AS A PROBABLE CAUSE. AFTER COMPLETING PERMANENT REPAIRS, LINE 1655 WAS RETURNED TO SERVICE ON FEBRUARY 19, 2020. ANTICIPATING ALTERNATING CURRENT (AC) STRAY CURRENT AS A PROBABLE CAUSE, A TEMPORARY SOLID-STATE DE-COUPLER WAS INSTALLED BETWEEN LINE 1655 AND THE SR 74 CASING. AN ADDITIONAL FIVE CASINGS WERE CONNECTED TO THE PIPELINE THROUGH SOLID STATE DE-COUPLERS TO PROVIDE ADDITIONAL MITIGATION AGAINST AC DENSITY ON LINE 1655. IN JANUARY 2021, THE COMPANY RECEIVED AN AC STUDY REPORT AND MITIGATION RECOMMENDATIONS FROM A THIRD-PARTY CONTRACTOR. AFTER REVIEWING THE REPORT, THE COMPANY REQUESTED ADDITIONAL MODELING TO BE COMPLETED USING A MORE STRINGENT AC DENSITY THRESHOLD DUE TO COMPANY PROCEDURES THAT HAVE BEEN UPDATED SUBJECT TO THE ADDITIONAL STRINGENT STANDARD. AS OF MARCH 31, 2021, THE NEWLY INTRODUCED MODELING IS ONGOING. ONCE COMPLETED, A PROJECT WILL BE IMPLEMENTED TO INSTALL THE ADDITIONAL MITIGATION MEASURES. AS PREVIOUSLY NOTED, TEMPORARY MITIGATION IS CURRENTLY IN PLACE ON 1655 TO HELP MITIGATE AC CONCERNS. MODELING WAS RECENTLY COMPLETED FOR 1655. THE MODELING INDICATED UNMITIGATED (WITHOUT THE TEMPORARY MITIGATION MEASURES IN PLACE) STEADY STATE VOLTAGES OVER 15 VAC AS WELL AS CURRENT DENSITIES OVER 30 A/M2. JANUARY 2022, THE AC VOLTAGE STUDY WAS COMPLETED, A NEW MITIGATION PROJECT IS IN PROCESS AND WE ARE CURRENTLY IN THE PERMITTING STAGES TO INSTALL APPROXIMATELY 4,500 FEET OF MITIGATION RIBBON ALONG THE PIPELINE, SIX FAULT MITIGATION ELECTRODES, ADDITIONAL COUPON TEST STATIONS, CONVERSIONS OF ALL TEST STATIONS IN THE AREA TO ""DEAD FRONT"" TEST STATIONS, AND APPROXIMATELY 15 GRADIENT CONTROL MATS AT EXISTING TEST STATIONS. THE PIPELINE HAS BEEN TEMPORARILY GROUNDED THROUGH SOLID STATE DECOUPLERS TO EXISTING CASINGS TO MITIGATE RISKS ASSOCIATED WITH HIGH AC CURRENT DENSITY AND INDUCED AC POTENTIALS. THESE TEMPORARY MEASURES WILL BE DISCONNECTED UPON COMPLETION OF THE PROJECT. THE TEMPORARY MEASURES DO NOT AFFECT THE CATHODIC PROTECTION OF THE PIPELINE. PROJECT COMPLETION IS CURRENTLY SCHEDULED FOR Q3 2022. PLEASE NOTE QUESTION E1A. WOULD NOT ACCEPT 12140 (MSCF/D) AS AN ENTRY FOR FLOW RATE. THE FLOW RATE AT THE TIME OF THE INCIDENT HAS BEEN ENTERED AS 12.14 (MMCF/D).