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L-0 BLADE FAILURE INVESTIGATION AT SOUTH TEXAS PROJECT

A last-stage (L-0) turbine blade failure was experienced at South Texas Project Unit 2 shortly after restart from the Fall 2002 refueling outage. This unit has one high-pressure turbine and three tandemcompound low-pressure turbines with 40-inch last-stage blades. The blade that failed was in the middle LP turbine (LP22) and subsequent non-destructive examination indicated that approximately half of the 266 blades in the L-0 row of this turbine had cracks. A significant number of L-0 blades in LP turbine connected to the HP (LP23) also had cracks but the LP turbine connected to the generator (LP21) was crack free. Inspections performed during the prior Unit 2 outage in Spring 2001 had identified two cracked blades in LP23. Laboratory evaluation of the cracking from both outages indicates the failure mechanism to be high cycle fatigue (HCF), initiating at the trailing edge, concave side of the steeple outermost fillet radius. Structural Integrity Associates (SI) was contracted to assist with the L-0 blade failure investigation. The investigation included a comprehensive testing, analysis and monitoring program to identify the root cause of the cracking and to help identify remedial measures.