Advanced NDE inspection methods for detection of SCC in blade attachments and blade roots

摘要

Power plant operators are often forced to make "release-repair-replace" decisions concerning components failed or reaching their designed life, thus reducing their availability. Possible failure of components, functional loss and personnel injuries therefore can't be excluded. Therefore, an adequate assessment of the remnant life of steam turbine components is a key issue in life management of steam turbines, and, therefore, in optimisation of inspection and maintenance concepts of power plants. To prevent such events, a defect assessment procedure needs the assessment of the actual and exact material condition of stressed components. Investigation of service lifetime of turbine components gains therefore considerably significance. SIEMENS Power Generation Group (Siemens PG) has developed a concept for service life analysis of highly-stressed turbine components which takes account of factors such as year of manufacture, i.e. the forging process, materials and service conditions to enable power plant operators to initiate timely actions to ensure future safe and reliable plant operation. In addition to material databases which contain not only material criteria but also act as a repository for long-term empirical data, nondestructive examination (using ultrasonic, eddy-current, magnetic-particle and liquid penetrant techniques) has an increasingly important role to play in providing precise descriptions of the condition of examined turbine components. Especially test methods, which ensure mechanized in-situ tests without additional expenditures for disassembling of blades and blade attachments are required to fulfil the prerequisites of the service- NDE on power plants. The paper describes several advanced inspection techniques, which ensure an reliable ultrasonic inspection of LP turbine blade attachments during outages. The used inspection technique allows the inspection of blade attachments grooves of an nuclear LP turbine rotor were even smallest indications of possible defects can be detected. Furthermore the application of advanced phased array inspection technique for blade roots of LP turbine rotor is described. By using this advanced technology an inspection of the most critical areas of blade roots is possible without dismantling from the rotor.