PIEDMONT NATURAL GAS CO INC

Incident Narrative

IN PIEDMONT NATURAL GAS' NASHVILLE OPERATIONS DISTRICT, AN EVENT OCCURRED ON A 12"" TRANSMISSION (LINE M) PIPELINE THAT OPERATES BETWEEN THE BORDEAUX REGULATOR STATION AND COUNTY HOSPITAL REGULATOR STATION AT APPROXIMATELY 12:30 AM LOCAL TIME ON AUGUST 2, 2012. THE EVENT SITE IS NEAR THE INTERSECTION OF CLARKSVILLE HWY AND HWY 12. THERE WERE NO NOTED INJURIES OR FATALITIES FROM THIS EVENT. THE LOCAL FIRE DEPARTMENT EVACUATED AREA RESIDENCES. LANE CLOSURES DID OCCUR DUE TO DEBRIS FROM ESCAPING GAS. DAMAGE WAS SUSTAINED TO AREA STRUCTURES DUE TO DEBRIS FROM THE FORCE OF THE ESCAPING GAS. THE PIPELINE WAS OPERATING AT APPROXIMATELY 620 PSIG AT THE TIME OF THE EVENT. GAS CONTROL NOTED THE EVENT DUE TO SCADA ALARMS. NOTIFICATION WAS ALSO RECEIVED BY THE CALL CENTER FROM LOCAL RESIDENCES. FIRST RESPONDERS WERE DISPATCHED BY BOTH GROUPS. NASHVILLE OPERATIONS PERSONNEL ASSESSED THE SITUATION AND VALVED OFF THIS APPROXIMATE 2.1 MILE SECTION OF PIPELINE WHILE COORDINATING WITH GAS CONTROL TO ENSURE SYSTEM PRESSURE AND FLOW REQUIREMENTS WERE BEING MET. NOTIFICATIONS WERE MADE TO BOTH THE TENNESSEE REGULATORY AUTHORITY (TRA) AND THE NATIONAL RESPONSE CENTER BASED ON INITIAL ESTIMATES THAT COST WOULD EXCEED $50,000 FOR REPAIRS INCLUDING COST OF LOST GAS. SIX RESIDENTIAL CUSTOMER PREMISES WERE IMPACTED BY THE CLOSURE OF THIS SECTION OF PIPELINE. ALL IMPACTED CUSTOMERS WERE CONTACTED TO INFORM THEM OF THE SITUATION AND EXPECTATION OF OUTAGE TIMELINES. THERE WAS ALSO AN IMPACT TO VANDERBILT UNIVERSITY DUE TO THE REDUCTION IN OVERALL SYSTEM PRESSURES UNTIL ALTERNATIVE FLOW PATHS OCCURRED. LINE REPAIRS WERE MADE TO THE DAMAGED SECTION OF PIPELINE. INSTALLATION OF LAUNCHER AND RECEIVER WAS COMPLETED AND THE ENTIRE 2.1 MILES OF PIPELINE WAS SMART PIGGED WITH A CALIPER TOOL AND HYDROTESTED PRIOR TO BEING REINSTATED INTO SERVICE. THIS WORK EFFORT WAS COMPLETED AND LINE M WAS RETURNED TO FULL SERVICE ON AUGUST 20, 2012 AT APPROXIMATELY 2:00 PM LOCAL TIME. DNV, AN INDEPENDENT FORENSICS LABORATORY IN COLUMBUS, OHIO, INVESTIGATED THIS INCIDENT AND DETERMINED THAT MECHANICAL DAMAGE DURING ORIGINAL PIPELINE CONSTRUCTION OCCURRED AND CREATED LINEAR DENTS ON THE BOTTOM SIDE OF A 23-FOOT LENGTH OF THE PIPE. RE-ROUNDING CRACKS FORMED IN THE DENTS, THEN GREW LARGER OVER TIME AND NORMAL OPERATION OF THE PIPELINE, EVENTUALLY RESULTING IN THE FAILURE.