NORTHERN NATURAL GAS CO

Incident Narrative

ON MAY 22, 2023, AT 1409 HOURS, A PIPELINE TECHNICIAN WAS PERFORMING EXCAVATION STANDBY FOR A ROAD CONSTRUCTION PROJECT WHEN HE DISCOVERED DISCOLORED SOIL IN THE AREA OF THE M500A VENTURA TO FARMINGTON A LINE AT MILEPOST 98.47. HE IMMEDIATELY RETRIEVED HIS LEAK DETECTION DEVICE FROM HIS TRUCK AND PERFORMED A BAR HOLE LEAK DETECTION SURVEY. THE INITIAL INDICATIONS WERE IN THE 250 TO 300 PARTS PER MILLION RANGE. THIS IS A CASED CROSSING AND INDICATIONS FROM THE CASING VENT WERE APPROXIMATELY 21% LEL. THE GRADE 2 LEAK SHUT DOWN THE ROAD CONSTRUCTION ACTIVITIES SO THAT A LEAK INVESTIGATION COULD BEGIN. MNOPS WAS INITIALLY NOTIFIED AT 1546 HOURS, BECAUSE OF THE DECISION TO CLOSE THE ROAD AND SHUT DOWN CONSTRUCTION ACTIVITIES. THE SITE WAS SECURED. ON MAY 22, 2023, AT 18:13, THE DECISION WAS MADE TO REPLACE THE CROSSING, REMOVING THE CASING IN THE PROCESS. AT THIS POINT THE COST ESTIMATE WOULD LIKELY EXCEED THE REPORTING THRESHOLD. THE LEAK WAS BELIEVED TO BE FROM A CRACKED WELD INSIDE OF THE CASING. THE SUSPECTED WELD HAS BEEN SENT TO A LAB FOR FURTHER ANALYSIS. A 36-INCH-LONG PIPE SAMPLE, WITH AN ACETYLENE GIRTH WELD LOCATED IN THE CENTER, WAS SUBMITTED TO AN INDEPENDENT LAB FOR ANALYSIS. LAB RESULTS WERE RECEIVED ON AUGUST 3, 2023. THE ACETYLENE WELD WAS INSPECTED AND FOUND TO BE SOUND WITH NO CRACKING. THE EXACT LEAK LOCATION WAS NOT FOUND IN THE SAMPLE SUBMITTED TO THE LAB. THE SAMPLE SUBMITTED HAD SIGNIFICANT EXTERNAL CORROSION PITTING. THE EVIDENCE OF EXTERNAL PITTING, AND THE SEVERITY OF THE PITTING IN SOME AREAS OF THE SUBMITTED SAMPLE, LEAD US TO BELIEVE THAT CORROSION PENETRATING THROUGH THE PIPE WALL AND GENERATING A PIN HOLE IN A DISCARDED PIECE OF PIPE CAUSED THE LEAK.