NORTHERN NATURAL GAS CO

Incident Narrative

ON MARCH 20, 2017, DURING A LIDAR GAS LEAK SURVEY OF THE MARQUETTE MAINLINE (MIM10101-M433B) A VERY LOW LEVEL, 111 PART PER MILLION LEAK WAS DISCOVERED NEAR MP 62.53. THE AREA IS REMOTE, WOODED AND CLASS 1 WITH NO NEARBY ROADS OR STRUCTURES. THE LEAK CAUSE WAS FOUND TO BE A MINOR CRACK IN A GIRTH WELD. ALTHOUGH THE REPAIR COULD HAVE BEEN COMPLETED WITH A LEAK CLAMP OR SLEEVE, NORTHERN ELECTED TO CUT OUT THE GIRTH WELD AND SUBMIT IT FOR FURTHER ROOT CAUSE ANALYSIS AS A PREVENTIVE AND MITIGATIVE MEASURE. THIS ADDITIONAL WORK DROVE THE COST OVER THE $50,000 REPORTING LIMIT. THIS LEAK WAS CONSIDERED A GRADE 3 LEAK (IN ACCORDANCE WITH GPTC GUIDE MATERIAL FOR THE CLASSIFICATION OF LEAKS, WHICH ARE CONSIDERED NON-HAZARDOUS AND EXPECTED TO REMAIN SO AND COULD HAVE BEEN LEFT TO ON-GOING MONITORING) SO NO NRC REPORT WAS MADE AND THE REPAIR WAS NEVER HANDLED BY THE COMPANY AS ANYTHING BUT ROUTINE. NORTHERN IS SUBMITTING THIS REPORT ON THE RECOMMENDATION OF THE PHMSA ACCIDENT INVESTIGATION DIVISION. NORTHERN DISAGREES THAT THIS LEAK CONSTITUTED AN INCIDENT SINCE IT WAS A GRADE 3 LEAK. THE LEAK WAS FOUND BY A HELICOPTER BASED INSTRUMENT USING LIGHT DETECTION AND RANGING (LIDAR) TECHNOLOGY. THIS SURVEY IS A PREVENTIVE AND MITIGATING MEASURE NORTHERN CONDUCTS WHICH IS BEYOND PIPELINE SAFETY REGULATORY REQUIREMENTS. IT IS VERY ACCURATE AND CAN LOCATE LEAKS MUCH SMALLER THAN COULD BE DETECTED BY HAND-HELD INSTRUMENTS OR EMPLOYEE SURVEYS. IN THIS CASE, THE LEAK WAS SIZED AT 111 PARTS PER MILLION. NORTHERN REPAIRS ALL LEAKS, REGARDLESS OF CLASSIFICATION, SO FOLLOWING CONFIRMATION, A REPAIR PROJECT WAS IMPLEMENTED. NORTHERN HAD OTHER OPTIONS TO REPAIR THE LEAK INCLUDING RELATIVELY LOW COST INSTALLATION OF A LEAK CLAMP OR SLEEVE TO A MORE COSTLY CUT OUT AND REPAIR OPTION. NORTHERN CHOSE THE CUT OUT AND REPLACE OPTION BECAUSE ALTHOUGH MORE COSTLY, IT WOULD ALLOW THE COMPANY TO SEND THE GIRTH WELD TO A METALLURGICAL LABORATORY FOR FAILURE ANALYSIS. THIS INFORMATION IS THEN USED TO PREVENT OCCURRENCE OF A SIMILAR INCIDENT.