ENOGEX LLC

Incident Narrative

ON WEDNESDAY JULY 7, 2010 AT APPROX 10:00 PM ENOGEX GAS CONTROL RECEIVED A HIGH PRESSURE ALARM AT THE AEP RIVERSIDE POWER STATION LOCATED IN JENKS, OKLAHOMA. AT 10:40 PM AN ENOGEX EMPLOYEE ARRIVED AT THE POWER STATION TO ASSESS THE SITUATION. THE EMPLOYEE WAS GREETED AT THE MAIN FACILITY ENTRANCE BY AN AEP INCIDENT COMMANDER. LOCAL EMERGENCY RESPONDERS FROM THE JENKS FIRE AND POLICE DEPARTMENTS VOLUNTARILY EVACUATED 70 PEOPLE FROM NEARBY HOMES PRIOR TO THE ARRIVAL OF ENOGEX PERSONNEL. AT 10:48 PM THE ENOGEX EMPLOYEE WAS ESCORTED TO THE LOW PRESSURE GAS YARD BY THE AEP INCIDENT COMMANDER. THE ENOGEX EMPLOYEE DISCOVERED NATURAL GAS RELIEVING TO ATMOSPHERE FROM TWO (2) 4 INCH BY 6 INCH PRESSURE SAFETY VALVES (PSV) AND TWO (2) 6 INCH BY 8 INCH PRESSURE SAFETY VALVES (PSV). UPON ENTERING THE GAS YARD, THE EMPLOYEE SMELLED AN ODOR OF MERCAPTAN AND HIS PERSONAL GAS MONITOR ALARM ACTIVATED, WHICH INDICATED THE PRESENCE OF A FLAMMABLE MIXTURE OF NATURAL GAS IN AIR. THE EMPLOYEE SAW THAT A 3/4 INCH PIPE NIPPLE, WHICH WAS A PORTION OF THE PRESSURE REGULATOR SENSING ASSEMBLY, HAD BROKEN RESULTING IN TWO (2) DEMAND REGULATORS TRAVELING TO THE FULLY OPEN POSITION, THUS INCREASING THE OPERATING PRESSURE DOWNSTREAM OF THE REGULATORS TO EQUAL THE 150 PSIG SET POINT OF THE FOUR (4) PSVS. AT 11:08 PM ENOGEX GAS CONTROL CLOSED AN AUTOMATED PIPELINE VALVE LOCATED UPSTREAM OF THE LOW PRESSURE GAS YARD TO ISOLATE THE GAS YARD FROM THE PIPELINE. NATURAL GAS CONTINUED TO ESCAPE TO ATMOSPHERE THROUGH A 3/4 INCH PIPE FITTING. AT 11:14 PM ENOGEX EMPLOYEES ISOLATED THE REGULATOR PIPING TO END THE RELEASE OF NATURAL GAS. THE NIPPLE WAS REPLACED AND THE PRIMARY GAS LOAD TO THE POWER STATION RESUMED AT 1:05 AM. AN INTERNAL INCIDENT INVESTIGATION WAS PERFORMED TO DETERMINE THE ROOT CAUSE AND CAUSAL FACTORS OF THE INCIDENT. IT WAS DETERMINED THAT A 3/4 INCH THREADED PIPE NIPPLE BROKE AT THE THREADED CONNECTION TO A 3/4 INCH THREAD-O-LET WELDED TO THE PIPING IMMEDIATELY DOWNSTREAM OF ONE OF THE REGULATORS. THE FAILURE IS BELIEVED TO HAVE BEEN CAUSED BY EXCESSIVE VIBRATION AND/OR METAL FATIGUE. TO PROVIDE THE NECESSARY FINAL DEMAND PRESSURE TO THE CUSTOMER DURING A WIDE RANGE OF POWER STATION LOAD CONDITIONS, THE REGULATOR STATION DESIGN CONSISTS OF TWO REGULATORS, I.E. REGULATOR 1 AND REGULATOR 2, PLACED IN PARALLEL TO ONE ANOTHER. A SINGLE PNEUMATIC PRESSURE CONTROLLER PROVIDES THE NECESSARY LOADING PRESSURE TO EACH REGULATOR. A LOADING PRESSURE OF 3 TO 9 PSIG CONTROLS REGULATOR1 AND A LOADING PRESSURE OF 9 TO 15 PSIG CONTROLS REGULATOR 2. THE FAILURE OF THE PIPE NIPPLE IN THE PRESSURE SENSING LINE AND SUBSEQUENT LOSS OF PROCESS VARIABLE CAUSED REGULATOR 1 TO TRAVEL TO THE FULLY OPEN POSITION FOLLOWED BY REGULATOR 2. THIS CREATED AN INCREASE IN THE DOWNSTREAM FINAL DEMAND PRESSURE TO A PRESSURE EQUAL TO THE 150 PSIG SETPOINT OF FOUR PRESSURE SAFETY VALVES (PSVS) INSTALLED TO PROTECT THE DOWNSTREAM PIPING FROM ACCIDENTAL OVERPRESSURE. IT WAS DETERMINED THAT THE RESULTING ACTION OF THE TWO REGULATORS, ALONG WITH THE ACTIVATION OF THE FOUR PSVS DOWNSTREAM OF THE REGULATORS RESULTED IN THE UNCONTROLLED GAS RELEASE TO ATMOSPHERE. IT WAS DETERMINED THAT THE TIMELY RESPONSE BY ENOGEX PERSONNEL TO CONTROL THE GAS RELEASE WAS HINDERED BY THE FOLLOWING: 1)A MISCOMMUNICATION BETWEEN AEP PERSONNEL AND THE JENKS FIRE AND POLICE DEPARTMENTS. THE EMERGENCY RESPONSE PERSONNEL ARRIVED ON SCENE (AT MAIN GATE) WELL AHEAD OF ENOGEX PERSONNEL. TO PREVENT THE EMERGENCY RESPONSE PERSONNEL FROM ENTERING THE FACILITY, AEP WOULD NOT OPEN THE MAIN GATE FOR ENOGEX AS QUICKLY AS DESIRED. 2) A POTENTIALLY HAZARDOUS CONDITION INSIDE THE LOW PRESSURE GAS YARD, WHEREAS THE PRESENCE OF A FLAMMABLE GAS MIXTURE IN THE ATMOSPHERE PREVENTED ENTRY. DUE TO THE PRESENCE OF NATURAL GAS IN THE ATMOSPHERE, THE ENOGEX RESPONDER COULD NOT SAFELY ENTER THE LOW PRESSURE GAS YARD TO MANUALLY CLOSE ISOLATION VALVES. UPDATE MARCH 5, 2013: COMPLETED SECTION E.5.F.