ATLANTA GAS LIGHT CO

Incident Narrative

A 6-INCH HP STEEL MAIN WITH A BULL PLUG END CONNECTED BY A STYLE 700 POSI-HOLD COMPRESSION COUPLING (MARKED WITH A 300 PSI PRESSURE RATING AND TESTED TO 2X WORKING PRESSURE (600 PSI) IN THE FACTORY DURING PRODUCTION) SEPARATED FROM THE MAIN. AS A RESULT OF THE SEPARATION, GAS SERVICE TO 452 CUSTOMERS WAS INTERRUPTED TO MAKE REPAIRS TO THE MAIN. AT THIS POINT IT WAS DETERMINED THAT THE INCIDENT RESULTED IN A COST MEETING THE THRESHOLD FOR REPORTING. PRIOR TO THE SEPARATION, THE MAIN ASSOCIATED WITH THE POSI-HOLD COMPRESSION COUPLING EXPERIENCED AN INCREASE IN PRESSURE APPROXIMATELY 10 PSIG ABOVE 110% OF MAOP. THE OVER-PRESSURE ABOVE THE ALLOWED 10% BUILD-UP WAS THE RESULT OF UNDERSIZED PIPING BETWEEN THE REGULATOR AND RELIEF VALVE WHICH LIMITED THE AMOUNT OF FLOW THE RELIEF VALVE COULD PASS TO STAY WITHIN THE NECESSARY TOLERANCE FOR BUILD-UP. THE REGULATOR STATION IN QUESTION HAS SINCE BEEN REBUILT WHERE THE PIPING AND FITTINGS ARE ADEQUATE FOR THE REQUIRED OVER-PRESSURE PROTECTION.