EVALUATION, REDESIGN, AND REPAIR OF A NUCLEAR STEAM TURBINE LOW-PRESSURE ROTOR SUFFERING FROM INTERGRANULAR STRESS CORROSION CRACKING

摘要

In 1995, intergranular stress corrosion cracking (IGSCC) was detected in low-pressure rotors at the Palo Verde Nuclear Generating Station. Following confirmation from the OEM that IGSCC was a class problem likely to affect all nine rotors at the plant, plant engineers embarked on an exhaustive campaign to define the magnitude of the problem, predict its progression, quantify its cost impact, and seek solutions in collaboration with consultants, after-market suppliers, industry organizations, and the OEM. A tiered strategy was developed (1) to ensure that appropriate condition-based repairs could be performed during regular maintenance outages without extending outage windows or reducing generating capacity; and (2) to provide a long-term solution. In October 2000, a "longshank" repair was performed on one rotor; this entailed machining to drop the radial height of the dovetail and installing new blades designed to accommodate the reduced wheel diameter. Successful completion of the longshank operation within a 15-day window met station goals of returning a safe rotor to service without impacting the outage schedule and without loss of generation. Meanwhile, a business case was developed justifying that procurement of new rotors capable of providing additional output represents an effective long-term solution.