SOUTHERN NATURAL GAS CO

Incident Narrative

AT 14:19 EST ON 02/21/2019 SOUTHERN NATURAL GAS COMPANY (SNG) WAS NOTIFIED BY THE FIRE DEPARTMENT THAT THERE WAS AN ODOR AND PLUME OF GAS ABOVE A PIPELINE OPERATED BY SNG. AT 15:20 EST SNG PERSONNEL ARRIVED ON SITE. AT 18:39 EST THE SEGMENT WAS ISOLATED. AS A PRECAUTION THE HOME NEAR THE INCIDENT WAS EVACUATED AND THE OWNER STAYED WITH A RELATIVE FOR ONE NIGHT. THE FIRST VISUAL OBSERVATION OF THE RELEASE POINT IDENTIFIED THAT FOUR FACTORY INSTALLED BOLTS USED TO HOLD THE LOWER TRUNNION TO THE BALL VALVE WERE FOUND BROKEN OFF. THE UNINTENTIONAL AMOUNT OF GAS RELEASED WAS 600.3 MCF. TO REPAIR THE ISSUE THE DAMAGED VALVE WAS REMOVED AND BLIND FLANGES WERE INSTALLED ON BOTH ENDS OF THE PIPELINE. ON 02/24/2019 THE LINE WAS PURGED AND PUT BACK INTO SERVICE. THE ABNORMALLY HIGH REPAIR COSTS WERE DUE TO SNG CHOOSING TO MOBILIZE ITS CONTRACTOR AND WORK THROUGH THE WEEKEND TO MAKE THE REPAIRS SO THAT THE PIPELINE SYSTEM COULD BE RESTORED TO FULL CAPACITY AS SOON AS POSSIBLE, THUS MINIMIZING THE IMPACT TO DOWNSTREAM CUSTOMERS. THE ESTIMATED COST FOR REPAIRING THIS ISSUE UNDER NORMAL CIRCUMSTANCES IS $40,000. AFTER A METALLURGICAL ANALYSIS, THE FAILURE OF THE BOLTS WAS DETERMINED TO BE ATTRIBUTED TO HYDROGEN EMBRITTLEMENT, IN THE FORM OF HYDROGEN-STRESS CRACKING. THE TENSILE STRENGTH AND CHEMICAL COMPOSITION OF THE BOLTS CONFORM TO THE REQUIREMENTS OF ASTM A193 GRADE B7 MATERIAL. HOWEVER, THE BOLTS DID NOT MEET THE ASTM A193 B7 HARDNESS SPECIFICATION. THE BOLTS HAD A HARDNESS OF 40 HRC, WHICH EXCEEDS THE MAXIMUM ASTM A193 B7 HARDNESS REQUIREMENTS OF 35 HRC. THE HARDNESS CONDITION INCREASED THE MICROSTRUCTURE'S SUSCEPTIBILITY TO HYDROGEN CRACKING. NO EVIDENCE OF OVER-TORQUING, STRESS CORROSION CRACKING, OR OTHER METALLURGICAL IRREGULARITIES WAS FOUND. 48-HR NRC REPORT UPDATE NUMBER IS 1238409.