TRANSCONTINENTAL GAS PIPE LINE COMPANY

Incident Narrative

FEBRUARY 5TH 2020: THE 40A40 MAINLINE BLOCK VALVE IS A REDUCED PORT VALVE THAT IS SCHEDULED FOR REPLACEMENT IN JUNE. IN PREPARATION FOR THAT PROJECT A CREW WAS HAND EXCAVATING THE VALVE ON FEBRUARY 5TH TO LOCATE THE WELD AND CONCRETE SUPPORTS. WHILE BACKFILLING THE EXCAVATION BY HAND, A SMALL GAS LEAK WAS HEARD AND A STOP WORK WAS CALLED. INVESTIGATION OF THE GAS LEAK IDENTIFIED THAT THE LEAK WAS COMING FROM A SMALL CRACK ON A FITTING CONNECTED TO THE BODY DRAIN VALVE. IT WAS KNOWN THAT IF THE PRESSURE COULD BE RELIEVED FROM THE VALVE BODY, THE LEAK WOULD BE STOPPED. FEBRUARY 5TH - 6TH: SEVERAL EFFORTS WERE MADE TO STOP THE LEAK BUT THOSE EFFORTS WERE UNSUCCESSFUL. FEBRUARY 7TH: DUE TO THE INABILITY TO STOP THE LEAK BY BLOWING DOWN THE VALVE BODY, THE ONLY OTHER OPTION TO STOP THE LEAK WAS TO REMOVE THE PRESSURE FROM THE PIPELINE. DUE TO THE LEAK BEING LOCATED ON A MAINLINE BLOCK VALVE, ONE SECTION OF THE PIPELINE UPSTREAM AND DOWNSTREAM HAD TO BE ISOLATED TO RELIEVE PRESSURE. OPERATIONS AND PROJECT PERSONNEL INVESTIGATED OPTIONS TO ACCELERATE VALVE REPLACEMENT OR REPAIRS. AFTER CONSIDERING ALL ALTERNATIVES THE $50,000 THRESHOLD WAS GOING TO BE EXCEEDED AND THE NRC WAS NOTIFIED. FEBRUARY 10TH: THE PIPELINE WAS ISOLATED AND DECOMPRESSION STARTED TO AVOID BLOWING DOWN ~26MMSCF IN GAS. THE LEAK WAS FREQUENTLY CHECKED BY OPERATIONS TO ENSURE THAT THE LEAK RATE DID NOT INCREASE. RECOMPRESSION WAS COMPLETE AND THE REMAINING PRESSURE (44 PSIG) WAS BLOWN DOWN TO ATMOSPHERE. 2/28/2020 - UPDATE - AFTER FURTHER INVESTIGATION, THE LEAK WAS NOT DUE TO CORROSION. THE 1/4 INCH NIPPLE HAS A VISIBLE CRACK INSIDE WHERE THE THREADS STOPPED ENTERING THE 1/2 INCH X 1/4 INCH REDUCER. IT APPEARS THAT THE 1/4 INCH NIPPLE WAS BENT AT SOME POINT IN TIME CAUSING THE CRACK SINCE THE CRACK AREA ITSELF IS CLEAN AND SHINY.