NORTHERN NATURAL GAS CO — Gas transmission and gathering — incident on 2017-03-20

Gas transmission and gathering incident in Not Within a Municipality, HOUGHTON County, MI. Reported cause: MATERIAL FAILURE OF PIPE OR WELD. Reported consequences: 0 fatalities, 0 injuries, 10 NATURAL GAS released, $997,500 reported property damage. Operator-reported incident data submitted to PHMSA, generally within 30 days. Records may be supplemented or corrected and do not represent final agency causal findings.

Report number: 20170078.

Operator ID: 13750.

Reported incident date: 3/20/2017 12:20.

Location detail: 63.52

Cause detail: DESIGN-, CONSTRUCTION-, INSTALLATION-, OR FABRICATION-RELATED

Cause detail: 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.

PHMSA trend classification: significant incident, not serious.

PHMSA standardized cause: MATERIAL FAILURE OF PIPE OR WELD — CONSTRUCTION, INSTALLATION OR FABRICATION-RELATED.

PHMSA indexed costs: $1,000,060 reported total cost, $488,873.676 in 1984 dollars, $1,203,875.056 in current-year dollars.

PHMSA trend flags, standardized causes, and indexed costs are analytical fields added to operator-reported incident data. They do not represent final agency causal findings.