TRANSCONTINENTAL GAS PIPE LINE COMPANY

Incident Narrative

ON 4/12/22, A SEGMENT OF MAINLINE A RUPTURED IN THE VALVE YARD OF STATION 90 COMPRESSOR FACILITY. NO EXPLOSION, FIRE OR INJURY OCCURRED. LOCAL OPERATING PERSONNEL PROVIDED TEMPORARY TRAFFIC CONTROL FOR ~30 MINUTES FOLLOWING THE RELEASE. NO OTHER PUBLIC IMPACT RESULTED FORM THE RELEASE. MAINLINE A IS ONE OF 5 PARALLEL PIPELINES THAT RUN THROUGH THE FACILITY. NO OTHER PIPELINE WAS INVOLVED OR DAMAGED DURING THE INCIDENT. OPERATING PERSONNEL AT THE FACILITY IMMEDIATELY INITIATED A COMPLETE COMPRESSOR STATION ESD AND PRESSURE BLOWDOWN. MAINLINE A WAS ISOLATED BETWEEN STATION 90 AND THE NEAREST PIPELINE ISOLATION VALVE WITHIN 12 MINUTES OF THE RUPTURE. THE NRC WAS NOTIFIED OF THE INCIDENT 45 MINUTES FOLLOWING THE RUPTURE. THE PIPELINE SEGMENT THAT FAILED WAS A 30-INCH OUTSIDE DIAMETER, 0.500-INCH WALL THICKNESS BETHLEHEM STEEL PIPE MANUFACTURED IN 1957 THAT WAS PROTECTED FORM CORROSION WITH EXTERNAL COATING AND IMPRESSED CURRENT CATHODIC PROTECTION. THE FRACTURE INVOLVED PIPE INSTALLED WITH A PIG LAUNCHER IN 1959 AND PIPE INSTALLED DURING MODIFICATION OF THIS PIG LAUNCHER IN 1997. METALLURGICAL ANALYSIS CONCLUDED THE RUPTURE ORIGINATED IN A HARD SPOT IN THE BODY OF PIPE INSTALLED IN 1959. ANALYSIS FURTHER IDENTIFIED A CRACK HAD DEVELOPED AT THE RUPTURE ORIGIN IN A MICROSCOPIC CORROSION PIT. INVESTIGATION CONCLUDED THE PIPELINE RUPTURE RESULTED FROM A HYDROGEN-ASSISTED STRESS CRACK THAT DEVELOPED IN A PREEXISTING HARD SPOT, WHICH EXTENDED THROUGH THE ENTIRE PIPE WALL. THE BRITTLE STRUCTURE OF THE HARD METAL ALLOWED THE STRESS CRACK TO PROPAGATE TO THE POINT OF FRACTURE. INVESTIGATION FURTHER IDENTIFIED ENVIRONMENTALLY ASSISTED CORROSION IN THE FORM OF A MICROSCOPIC PIT AND ELEVATED CATHODIC PROTECTION ELECTRONEGATIVITY AS CONTRIBUTING FACTORS TO DIRECT CAUSES.