TABLE OF CONTENTS The steam path can be subjected to a number of operational events that degrade the overall quality of the unit, and so degrade performance, both in terms of efficiency and availability. Under certain circumstances these damaging mechanisms can be sufficient to force the unit from service, and degrading influences can result in considerable expense to the owner.
Not every machine is subject to each of the "damage mechanisms" that follow. But each machine can be if the operational conditions are such that the opportunity for their occurrence exists.
This chapter will examine the most common of these, and where possible provide an explanation of their characteristics, some brief explanation of the circumstances that allows them to occur and provide some guidance to their avoidance, if such avoidance is possible.
Some of these mechanisms are well understood and some allowance is made for them in the original configuration of both the cycle and the details of the turbine unit. Other mechanisms are often unanticipated, and can be particularly present in units of a prototype design when the boundaries of design are extended and experience extrapolated to provide guidance.
There are many instances when the blade vanes, both stationary and rotating, are damaged by impact with solid objects that have been generated within, or gained access to the steam path. There are a number of sources for these objects, which can be of various sizes depending upon their origin. The damage they cause will depend upon their...
