TRANSCONTINENTAL GAS PIPE LINE COMPANY

Incident Narrative

MEASUREMENT PERSONEL DETECTED A STRONG GAS ODOR WHILE AT THE EAST RUTHERFORD M&R ON 3/10/2014. IT WAS DETERMINED THAT THE LEAK WAS COMING FROM BELOW GROUND NEAR A MAIN LINE ""A"" TAP VALVE FEED FOR THE M&R STATION. MANAGEMENT WAS NOTIFIED AND BEGAN THE INVESTIGATION. SOIL WAS REMOVED FROM THE LEAK AREA AND A GAS DETECTOR WAS USED TO DETERMINE THAT A LEAK WAS INFACT PRESENT. THE LINE WAS DRAWN DOWN TO 150 PSIG THROUGH THE EAST RUTHERFORD M&R AND THEN BLOWN DOWN TO 0 PSIG . A CONTRACTOR WAS BROUGHT IN TO FULLY EXCAVATE AND MAKE THE NECESSARY REPAIRS (LEAKING PIPE SECTION WAS CUT-OUT AND REPLACED WITH NEW PIPE). IT WAS DETERMINED THAT A CRACK HAD FORMED ON THE MAIN LINE PIPE IN THE AREA WHERE THE HOT TAP NIPPLE WAS ATTACHED TO THE MAIN LINE PIPING. ONCE THE REPAIR WAS COMPLETE, THE LINE WAS PURGED OF AIR, PACKED TO LINE PRESSURE AND RETURNED TO SERVICE ON 3/13/2014. FINAL LEAK (METALLLURGICAL) EVALUATION - THE TOE CRACK OBSERVED IN THE MAIN LINE PIPE WAS DETERMINED TO BE A HYDROGEN INDUCED CRACK, OR COLD CRACK.THE HYDROGEN WOULD HAVE BEEN INTRODUCED DURING THE WELDING PROCESS, ALTHOUGH LOW-HYDROGEN ELECTRODES CAN HELP REDUCE THE POTENTIAL FOR HYDROGEN ENTRAPMENT. HARDENED MICROSTRUCTURES IN THE HEAT-AFFECTED ZONE OF A WELD CAN BE PRODUCED BY EXCESSIVE COOLING RATES AND THE ABSENCE OF EFFECTIVE PRE- AND POST-HEAT WELD PROCEDURES. THE AMOUNT OF PRE- AND POST-HEAT DEPENDS ON MULTIPLE FACTORS, INCLUDING BUT NOT LIMITED TO, THE WALL THICKNESS AND THE CARBON EQUIVALENT OF THE PIPE. RESIDUAL STRESSES CAUSED BY RESTRAINT INDUCED DURING WELDING ARE ALSO A CONTRIBUTING FACTOR TO HYDROGEN CRACKING.