COLORADO INTERSTATE GAS CO

Incident Narrative

ON JANUARY 17, 2019 AT APPROXIMATELY 11:55 PM LOCAL TIME, COLORADO INTERSTATE GAS (CIG) GAS CONTROL RECEIVED A TELEPHONE CALL FROM A THIRD-PARTY OIL AND GAS OPERATOR REPORTING A SOUND OF GAS RELEASING FROM OUR PIPELINE FACILITY AT THE L250A PIG LAUNCHER AND PIG RECEIVING FACILITY IN WELD COUNTY, COLORADO. UPON RECEIVING THE THIRD-PARTY REPORT, GAS CONTROL CALLED THE CIG AREA SUPERVISOR AND DISPATCHED HIM TO THE LOCATION. HE ARRIVED ON SITE AT 1:18 AM LOCAL TIME ON JANUARY 18, 2019 AND VERIFIED THAT THE GAS LEAK WAS IN FACT ON THE CIG L250 PIPELINE PIG TRAP FACILITY. AT 1:50 AM LOCAL TIME ON JANUARY 18, 2019, CIG INITIATED AN INTERNAL EMERGENCY-RESPONSE-LINE (ERL) TELEPHONE CALL TO DISCUSS THE AVAILABLE INFORMATION REGARDING THE GAS LEAK TO DETERMINE WHETHER DISCOVERY OF A REPORTABLE EVENT OCCURRED. SINCE THE 250A SEGMENT IMPACTED BY THE LEAK COULD NOT BE IMMEDIATELY ISOLATED UNTIL ALTERNATIVE GAS SUPPLIES FOR CIG'S CUSTOMERS SERVED FROM THAT SEGMENT COULD BE ARRANGED, CIG DECIDED TO ASSUME THE RELEASE VOLUMES WOULD EXCEED THE REPORTABLE THRESHOLD AND DECIDED TO NOTIFY THE NATIONAL RESPONSE CENTER (NRC) OF THE EVENT PRIOR TO ESTABLISHING THE ACTUAL VOLUMES RELEASED. IT WAS NOT UNTIL THE AFFECTED SEGMENT CONTAINING THE LEAK COULD BE ISOLATED AT 4:17 AM ON JANUARY 18, 2019, THAT CIG WAS ABLE TO ESTIMATE THE ACTUAL RELEASE VOLUME. DURING THE INITIAL INVESTIGATION, CIG CALCULATED THE TOTAL RELEASE VOLUME (3,282 MCF) AND DETERMINED IT HAD MET THE REPORTING REQUIREMENT FOR THE EVENT AT 3:55 AM ON JANUARY 18, 2019. THE NRC WAS NOTIFIED AT 2:04 AM LOCAL TIME ON JANUARY 18, 2019 (NRC NO. 1235460) OF THE GAS RELEASE WITH AN ESTIMATE TO BE GREATER THAN 3,000 MCF AND RESULTING IN A REPORTABLE EVENT. THE NRC LOGGED RECEIPT OF THE REPORT AT 2:09 AM LOCAL TIME. A COURTESY NOTIFICATION TO THE PHMSA INCIDENT INVESTIGATION TEAM WAS PROVIDED AT 2:38 AM LOCAL TIME THAT DAY. AT 3:06 PM LOCAL TIME ON JANUARY 18, 2019, ALL REPAIRS TO THE FACILITIES WERE COMPLETE AND RETURNED TO SERVICE. AT 3:54 PM LOCAL TIME ON JANUARY 18, 2019, A 48-HOUR UPDATE REPORT WAS CALLED INTO THE NRC (REPORT NO. 1235523) PROVIDING THE TOTAL VOLUME OF THE RELEASE (3,282 MCF) WITH CONFIRMATION THAT THERE WERE NO CUSTOMER IMPACTS DUE TO THE INCIDENT. THE NRC LOGGED THE RECEIPT OF THE REPORT AT 14:02 LOCAL TIME. THE 1' BLOW-OFF VALVE ASSEMBLY THAT FAILED WAS SENT FOR A COMPLETE METALLURGICAL ANALYSIS TO DETERMINE THE ROOT CAUSE OF THE FAILURE. FROM THE METALLURGICAL ANALYSIS, IT WAS DETERMINED THE ROOT CAUSE OF THE BUTT WELD FAILURE WAS CAUSED BY HIGH-CYCLE, LOW NOMINAL STRESS, UNIDIRECTIONAL-BENDING FATIGUE. OPERATIONS FIELD PERSONNEL OBSERVED THAT THE 1' BLOW-OFF VALVE ASSEMBLY WAS FOUND APPROXIMATELY 25 FEET FROM THE WELDED COUPLING LOCATED ON THE 250A PIPELINE FOLLOWING THE EVENT. THE THREADED NIPPLE END OF THE ASSEMBLY WAS LOCATED APPROXIMATELY 6-12 INCHES FROM THE REST OF THE VENT VALVE ASSEMBLY. THE VALVE WAS FOUND IN THE CLOSED POSITION. BASED ON THESE OBSERVATIONS, IT WAS CONCLUDED THAT THE WELDED END FAILED FIRST AND THE THREADED NIPPLE SEPARATED FROM THE VENT VALVE AFTER THE ENTIRE 1' BLOW-OFF VALVE ASSEMBLY WAS EJECTED AND IMPACTED WITH THE GROUND. THE METALLURGICAL ANALYSIS DID NOT IDENTIFY ANY MATERIAL COMPOSITION DEFICIENCIES OF THE ASSEMBLY. IN ADDITION NO EVIDENCE OF EXCESSIVE TORQUE WAS IDENTIFIED. CIG CONCLUDED THE ROOT CAUSE OF THE THREADED-END OF THE NIPPLE BLOW-OFF VALVE ASSEMBLY FAILURE RESULTED FROM THE ASSEMBLY IMPACTING THE GROUND SURFACE. THE ROOT CAUSE OF THE WELD FAILURE IS ASSOCIATED WITH A VIBRATION CAUSED FROM AN 8-INCH FLOW CONTROL VALVE AT THE REGULATOR STATION AT GATE 6. CIG FINALIZED A VIBRATION STUDY ON APRIL 24, 2019. RESULTS OF THE STUDY IDENTIFIED FACILITY MODIFICATIONS WILL BE NECESSARY TO HELP REDUCE VIBRATION AND UNTIL THESE CHANGES CAN BE COMPLETED, CIG WILL IMPLEMENT OPERATING CHANGES AS NEEDED TO HELP LOWER VIBRATION LEVELS.