NORTHERN NATURAL GAS CO

Incident Narrative

ON DECEMBER 22, 2022, AT 2106 FIELD OPERATIONS TECHNICIAN WAS NOTIFIED OF A VENTING RELIEF VALVE IN THE OGDEN COMPRESSOR STATION. IT WAS DETERMINED TO BE THE RELIEF VALVE DOWNSTREAM OF VALVE 113 ON THE DES MOINES A-LINE (IAB65001). ACCORDING TO DATA TRENDS THE RELIEF VALVE VENTED 20 TIMES FOR AN AVERAGE OF 40 SECONDS EACH FROM 2100 HOURS TO 2116 HOURS. HIGHEST PRESSURE RECORDED WAS 456 PSIG AT 2109 HOURS. AT 2116 HOURS THE PRESSURE RETURNED TO NORMAL OPERATING PRESSURE OF 355PSIG. THE INVESTIGATION REVEALED THE CAUSE OF THE OVERPRESSURE WAS DUE TO CONSTRUCTION DEBRIS IN THE WHISPER TRIM CAGE OF THE VALVE 49 REGULATOR. THE DEBRIS CAUSED THE REGULATOR TO NOT CLOSE COMPLETELY. THE TEAM HAD MIDWEST VALVE TO INSPECT THE VALVE AND FOUND THE DEBRIS IN THE REGULATOR CAGE. THE CAGE WAS CLEANED OF ALL DEBRIS. THE STEM AND SEAT WERE VERIFIED TO HAVE NO DAMAGE. NEW SOFT GOODS AND SEALS WERE INSTALLED IN THE REGULATOR. WORK WAS COMPLETED ON JANUARY 5, 2023. THE CONTRACTOR TESTED THE VALVE FOR PROPER OPERATION AND FOUND NO ISSUES WITH THE VALVE OPENING AND CLOSING. 04/05/23 UPDATE - THE DEBRIS FOUND IN THE WHISPER TRIM CAGE WAS MOST LIKELY FROM PIGGING OPERATIONS NOT CONSTRUCTION. ALSO, THE DES MOINES A-LINE (IAB65001) WAS MISTAKENLY LISTED AS A 380 MAOP. IT SHOULD READ 500 MAOP. IN 2016 NORTHERN HAD AN INCIDENT ON THE M640A BUSHTON TO TESCOTT MAINLINE NEAR I-70 IN KANSAS. NORTHERN WAS ISSUED A CORRECTIVE ACTON ORDER. AS A RESULT, NORTHERN VOLUNTARILY LOWERED THE MAOP ON ALL BARE, DRESSER COUPLED MAINLINES. NORTHERN HAS BEEN ABANDONING AND REMOVING THOSE MAINLINES. THE CAO DID NOT INCLUDE BRANCH LINES SO DES MOINES SHOULD NOT HAVE BEEN INCLUDED. THIS BRANCHLINE IS BEING REPLACED WITH A NEW 16-INCH C-LINE (IAB65003). THAT PIPELINE WILL BE IN-SERVICE BY NOVEMBER 1, 2023. AT THAT TIME THE A-LINE WILL BE SHUT OFF AND READIED FOR ABANDONMENT. THAT SHOULD ELIMINATE THE LAST 16-INCH AND ABOVE BARE, DRESSER COUPLED PIPELINE.