NORTHERN NATURAL GAS CO

Incident Narrative

ON APRIL 23, 2013, AT APPROXIMATELY 04:27 NORTHERN NATURAL GAS COMPANY'S OMAHA OPERATIONS COMMUNICATIONS CENTER RECEIVED A CALL FROM A DAVID WEISS WITH THE MONDOVI, WISCONSIN FIRE DEPARTMENT REPORTING THAT THERE APPEARED TO BE BLOWING NATURAL GAS 1/2 MILE SOUTH OF COUNTY ROAD A ON STEELE VALLEY ROAD ON PIPELINE NUMBER WIB 18601 AT A MILE POST OF 55.126. MR. WEISS INDICATED THAT EMERGENCY RESPONDERS WERE ON-SITE AND THAT THEY HAD BLOCKED OFF A SECTION OF THE ROAD. HE INDICATED THAT THERE WERE NO RESIDENCES IN THE IMMEDIATE AREA. A REPRENTATIVE FROM MIDWEST NATURAL GAS CALLED TO CONFIRM THAT NATURAL GAS APPEARED TO BE BLOWING FROM VENT CASINGS ON BOTH SIDES OF THE ROAD. THE LOCATION IS APPROXIMATELY FOUR MILES WEST OF THE TOWN OF MONDOVI, WISCONSIN. NORTHERN COMPANY EMPLOYEES WERE DISPATCHED TO THE SITE AND A GAS MANAGEMENT PLAN WAS DEVELOPED TO REDUCE PRESSURE ON THE THE PIPELINE TO APPROXIMATELY 520-550 PSIG FROM A TYPICAL 795 PSIG. PRESSURE WAS REDUCED BY PINCHING BLOCK VALVES AND LETTING CUSTOMER USAGE PULL THE PRESSURE DOWN ON THE LINE THEN CLOSELY MONITORING. EMERGENCY STOPPLE AND BYPASS PIPING WAS BROUGHT ON-SITE TESTED AND PLACED IN-SERVICE. MICHELS CONSTRUCTION, A CONTRACTOR, ASSISTED WITH EXCAVATION ACTIVITIES ON BOTH SIDE OF THE ROAD. UPON COMPLETION OF EXCAVATION A CRACK IN A PIPING GIRTH WELD WAS FOUND ON THE UNDER SIDE (SIX O'CLOCK POSITION) WHICH WENT ENTIRELY THROUGH THE PIPE, THE CRACK WAS APPROXIMATELY 4 1/2 INCHES LONG AND ONE SIXTEENTH OF AN INCH WIDE. THE STEELE COUNTY ROAD DEPARTMENT WAS CONTACTED AND AGREED THAT NORTHERN COULD OPEN CUT THE ROAD FOR INSTALLING NEW TESTED PIPE. NORTHEN WOULD BE RESPONSIBLE FOR RESTORATION OF THE ROAD AND HARD SURFACING. APPROXIMATELY 60-FEET OF NEW TESTED, COATED PIPE WAS INSTALLED. THERE WERE NO INJURIES, NO FIRE, NO EVACUATIONS AND NO LOSS OF SERVICE TO CUSTOMERS. THE PIPE WITH THE CRACKED GIRTH WELD WAS SENT TO AN OUTSIDE METALLURGICAL LABORATORY FOR ANALYSIS. A SUPPLEMENTAL REPORT WILL BE FILED WHEN RESULTS FROM THE METALLURICAL LABORATORY TESTS ARE RECEIVED AND A TOTAL COST OF THE REPAIRS IS COMPLILED. SUPPLEMENTAL/FINAL REPORT (REFERENCE INITIAL REPORT 20130040 - 15978 DATED 05/13/2013 - THE FINAL COST FOR THIS EVENT HAS BEEN UPDATED. A METALLURGICAL ANALYSIS WAS COMPLETED BY BRYAN LABORATORY, INC. WITH FINDINGS OF THAT THE PIPE AT BOTH GIRTH WELDS EXAMINED WERE FOUND TO EXHIBIT MISALIGNMENT AND APPEAR TO BE DISTORTED. EXTRANEOUS WELDING WIRE WAS NOTED PROTRUDING FROM THE INTERNAL PORTIONS OF THE WELD. THE CRACK WAS FOUND TO BE 6-INCHES LONG AND IN THE LOWER QUADRANT OF THE WELD. ""NECKING DOWN"", TYPICAL OF DUCTILE OVERLOADING FRATURING, WAS NOTED IN THE PIPE ON THE INTERNAL SURFACE OF THE CRACKED AREA. IN THE LABORATORIES OPINION, THE CRACK WAS CAUSED BY BENDING FORCES, AS SHOWN BY THE DISTORTION OF THE PIPE AT THE GIRTH WELD. BLACK DEPOSITS ALONG BOTH SIDES OF THE CRACK AT THE OUTSIDE SURFACE SHOWED THAT A CRACK APPROXIMATELY 0.025 INCHES DEEP PRECEDED FINAL SEPARATION. FINAL SEPARATION INITIATED AT THE PREEXISTING CRACK AND FINAL SEPARATION WAS BY DUCTILE OVERLOAD. A COPY OF THE METALLURICAL REPORT IS ATTACHED.