INTRODUCTION

Although most parts of the steam turbine are capable of suffering mechanical damage and do sustain it some areas or components suffer greater levels of deterioration than others. Why some areas in any unit are more susceptible than others is a function of many complex factors individual stress levels, stress concentration, the mode of operation, operating environment, and the manner in which the unit is maintained. Other critical factors involve the operating transients to which components are subjected. This diversity of factors that can influence the potential for damage precludes any ability to state a generalization of causes or of value. Despite this fact, the area of the unit having a considerable potential to affect performance and of raising the concern of the operating and maintenance engineer is the steam path.

Components of the steam path are subjected to high stresses, direct and alternating. Many parts operate at high temperatures. Often they are complex. These elements will also interact with others in unpredictable ways. These factors, when combined with load and steam temperature transients that commonly occur during operation, make the steam path highly sensitive and a prime candidate for deterioration. If populations of steam turbines were to be reviewed, there is a high probability that failures or problems within the steam path would be a significant cause of deteriorating performance for many of them. The rotating blades would pose a major cause within the steam path itself.

This chapter discusses strategies available to owners when they determine their units have suffered some form...