WILLIAMS GAS PIPELINE - TRANSCO

Incident Narrative

A CALL FROM A WILLIAMS EMPLOYEE WAS RECEIVED AT 6:15PM STATING THAT A LEAK ON 24"" MAINLINE A HAS BEEN DISCOVERED. AFTER HAVING NOTIFIED GAS CONTROL IN HOUSTON, SEVERAL SOUTH TEXAS DISTRICT EMPLOYEES WERE CONTACTED AND REQUESTED THAT THEY CLOSE BOTH BLOCK VALVES 10-A-70 AND 10-A 80, WHICH WOULD ISOLATE THE SECTION OF PIPELINE WHERE THE LEAK WAS LOCATED. THE PIPELINE WAS ISOLATED AND HAD BEEN MADE SECURE BY 7:15 PM. NRC WAS CONTACTED AT 7:37 PM AND ANY OTHER AGENCIES THAT WOULD NORMALLY BE INCLUDED IN THE NOTIFICATION PROCESS. THESE NOTIFICATIONS WERE COMPLETED BY 8:00 PM THAT EVENING.. A GAS HANDLING PLAN AND A WORK PLAN WERE GENERATED EARLY ON TUESDAY MORNING AND THE SECTION OF PIPELINE BETWEEN THE TWO BLOCK VALVE SETTINGS WAS BLOWN DOWN. A CONTRACTOR WAS DISPATCHED TO THE LOCATION AND ONCE THE PIPELINE WAS MADE SAFE, STARTED EXCAVATING THE LINE TO EXPOSE THE AREA OF THE LEAK. DURING THE EXCAVATION PROCESS, AN OLD AND MOSTLY CORRODED 2"" PIPELINE WHICH WAS ALREADY IN PIECES WAS UNCOVERED. THIS 2"" PIPELINE WAS LOCATED APPROXIMATELY 2 1/2"" ABOVE OUR 24"" PIPELINE. THIS 2"" PIPE WAS ABANDONED AND BEEN OUT OF SERVICE FOR SOME TIME. THE SOIL AROUND THE 2"" PIPELINE AND DOWN TO OUR PINHOLE LEAK WAS SATURATED WITH SOME TYPE OF PRODUCT THAT SMELLED VERY MUCH LIKE CONDENSATE. THE PINHOLE LEAK WAS LOCATED AND AFTER CLOSE INSPECTION, A 30' SECTION OF PIPE WAS CUT OUT AND REPLACED WITH NEW PRETESTED PIPE. THE ORIGINAL 24"" PIPE AT BOTH ENDS OF THE 30' SECTION WAS IN EXCELLENT CONDITION BOTH INTERNALLY AND EXTERNALLY. SOIL SAMPLES WERE TAKEN OF THE IMMEDIATE AREA AND WERE SHIPPED OVERNIGHT TO A LAB FOR FURTHER ANALYSIS. WILLIAMS HAD A METALLURGICAL TEST OF THE PIPE THAT WAS CUT OUT IN ORDER THAT IT CAN IDENTIFY THE ROOT CAUSE OF THE CORROSION AT THAT PARTICULAR SITE. THE 24"" PIPELINE WAS PURGED, PACKED AND PLACED BACK IN SERVICE AT 11:00 AM ON THURSDAY, APRIL 29TH, 2010. METALLURGICAL ANALYSIS CONFIRMED THAT THE REASON FOR THE LEAS WAS MICROBIOLOGICAL ON 6/2/2010. THE METALLURGICAL REPORT FOUND THE FOLLOWING; THE COAL TAR CORROSION PROTECTION THAT COATED THE PIPELINE WHEN IT WAS ORIGINALLY INSTALLED HAD BEEN SEVERELY DEGRADED IN THE AREA AROUND THE LEAK, PROBABLY BY A CHEMICAL SUBSTANCE THAT HAD APPARENTLY LEAKED FROM THE 2-INCH PIPELINE INSTALLED OVER THE 24-INCH LINE. VISUAL EXAMINATION OF THE LEAK SHOWED CORROSION PITTING ON THE OUTSIDE SURFACE. SOME OF THE PITS HAD A FIBROUS APPEARANCE INDICATING PREFERENTIAL ATTACK FOLLOWING THE PIPE AXIS. THE FIBROUS APPEARANCE WAS CHARACTERISTIC OF MICROBIOLOGICALLY-INFLUENCED CORROSION (MIC). METALLOGRAPHIC ANALYSIS OF THE CORROSION PITS SHOWED UNDERCUTTING AND PITS WITHIN PITS, WHICH ARE ALSO UNIQUE CHARACTERISTICS OF MIC. THE LEAK WAS CAUSED BY MIC, WHICH OCCURED AFTER THE COAL TAR COATING HAD BEEN DEGRADED EXPOSING THE BARE PIPE. THE PRESENCE OF SULFUR AND MOISTURE IN THE SOIL AROUND THE LEAK CREATED AN IDEAL ENVIRONMENT FOR MIC TO OCCUR.