TRANSCONTINENTAL GAS PIPE LINE COMPANY

Incident Narrative

DURING THE SEMI-ANNUAL LEAK SURVEY FLIGHT, AN ELEVATED CH4 LEVEL WAS INDICATED. A LOCAL OPERATIONS TECH USED HANDHELD RMLD TO VERIFY THE PRESENCE OF NATURAL GAS. IT WAS INITIALLY BELIEVED A BURIED THREADED CONNECTION IN THE BODY VENT PIPING OF VALVE WAS LEAKING. POTHOLING, VACUUM EXCAVATION, AND PROBING WERE USED TO DETERMINE THE LEAK LOCATION UPSTREAM OF MAINLINE BLOCK VALVE 145D1 WHERE INCREASED LEVELS OF NATURAL GAS WERE NOTED ONCE THE PROBE BAR WAS REMOVED. THE PIPELINE SEGMENT WAS ISOLATED AND BLOWN DOWN TO ALLOW FOR FURTHER EXCAVATION. ONCE PIPELINE WAS EXCAVATED, THE SOURCE OF LEAK WAS IDENTIFIED USING LEAK DETECTION LIQUID AT A WELD FITTING. X-RAYS OF THE SUBJECT WELD WERE TAKEN. A PLAN HAS BEEN FORMULATED AND APPROVED TO CUT OUT THE WELD THAT WAS LEAKING AND ALSO THE FITTING JUST DOWNSTREAM OF THE SUSPECT WELD. NEW PIPE AND FITTING WILL BE INSTALLED. ONCE THE SUSPECT WELD AND FITTING ARE REMOVED, IT WILL BE SENT TO LAB FOR A FULL METALLURGICAL ANALYSIS. THE WORK IS SET TO BEGIN THE WEEK OF 12/9/2019. UPDATE: CRACKING CONFINED TO WELD METAL. CRACKING MOST LIKELY OCCURRED BY A HYDROGEN ASSISTED CRACKING (HAC) MECHANISM. THE HAC CRACKING WAS MOST LIKELY FACILITATED BY THE HI-LOW OF THE JOINT FIT-UP, AND QUALITY OF APPLICATION OF THE ROOT PASS DURING CONSTRUCTION INSTALLATION. ANY UNDUE STRESSES ASSOCIATED WITH THE FINAL TIE IN WELD MAY HAVE CONTRIBUTED.