MISSOURI GAS ENERGY

Incident Narrative

THE 16"" STEEL GAS MAIN INCURRED A PARTIAL CIRCUMFERENTIAL BREAK. PRESSURE & MEASUREMENT DEPARTMENT CLOSED ISOLATION VALVES, LOWERED PRESSURES ON THE SYSTEM FROM 222 PSIG TO 35 PSIG. CONSTRUCTION CREWS INSTALLED A 16"" FULL CIRCLE BAND CLAMP TO STOP THE BLOWING GAS. THEY THEN INSTALLED A REPAIR WELD SLEEVE AS A PERMANENT REPAIR. VALVES WERE THEN OPENED AND PRESSURE RESTORED TO NOT EXCEED 177 PSIG UNTIL FURTHER INVESTIGATION IS COMPLETE. THIS PIPE HAS BEEN CATHODICALLY PROTECTED BY RECTIFIER SINCE 1964. CAUSE OF THE DAMAGE IS UNKNOWN AND STILL UNDER INVESTIGATION. SUPPLEMENTAL REPORT DATA (4/13/12): MISSOURI PUBLIC SERVICE COMMISSION FILED A REPORT DEC. 9, 2011 (CASE NO. GS-2011-0248), BASED ON THEIR SAFETY STAFF'S RECOMMENDATIONS. MGE AND MPSC SAFETY STAFF AGREED THAT MGE WILL REPLACE THE ENTIRE LENGTH OF THE MAYFAIR 16 INCH PIPELINE IN TWO PHASES. PHASE 1 WILL REPLACE THE SECTION WHERE THE INCIDENT OCCURRED AND WILL BE COMPLETED BETWEEN JUNE 1, 2012 AND OCTOBER 1, 2012. ONCE THE PIPELINE IS REMOVED FROM SERVICE, MGE WILL REMOVE THE REPAIRED SECTION OF PIPE THAT CAUSED THE ORIGINAL INCIDENT AND PERFORM AN INVESTIGATION OF THE FRACTURE TO DETERMINE THE CAUSE. NO OTHER DATA HAS BEEN DISCOVERED, TO DATE, TO DETERMIN THE CAUSE OF THE FRACTURE. FINAL REPORT DATA (3/28/2013): MGE COMPLETED REPLACEMENT OF THIS SECTION OF 16 INCH STEEL MAIN ON 11/06/2012. THE SECTION OF PIPE THAT CAUSED THE ORIGINAL INCIDENT WAS CUT OUT AND REMOVED FROM THE GROUND AND SENT FOR METALLURGICAL ANALYSIS. THE CONCLUSION FROM THE DATA COLLECTED FROM THE SCANNING ELECTRON MICROSCOPE (SEM) AND METALLOGRAPHIC WORK IS THAT THE FAILURE MECHANISM IS STRESS CORROSION CRACKING (SCC) WHICH RESULTED FROM SETTLEMENT OF THE SOIL UNDER THE 16 INCH STEEL GAS MAIN THAT WAS INSTALLED IN 1997, RESULTING IN A SIGNIFICANT TORSIONAL LOAD ON THE PIPE APPROXIMATELY 13 FEET TO THE WEST (POINT OF BREAK).