Abstract

Water Droplet Erosion (WDE) is defined as the progressive loss of original material from a solid surface due to continuous impingements of water droplets or jets. In this work, parameters affecting this wear phenomenon are discussed in detail through a literature review. The initial surface roughness as a parameter that may influence WDE process was not given attention in the literature. Therefore, its effect on erosion was studied experimentally. It was concluded that the initial surface roughness has a significant effect on the length of the incubation stage, and may influence the maximum erosion rate.
Another point tackled in this work is the WDE results representation. The traditional method of representing erosion results is through a plot between material loss and time. However, this plot neglects important information about the WDE experiment, for instance, the amount of water which has impacted the sample during the test. Therefore, in this work a new representation method of WDE test results was proposed. This new method represents WDE test results with respect to the applied kinetic energy per unit area. WDE erosion result for tests done on 12% Cr stainless steel were successfully represented and analyzed using this method.
Finally, the WDE found on ex-service steam turbine blades was studied. The progression of erosion on the surface of the blades was illustrated by the aid of SEM micrographs. This work confirmed that the formation of asperities and depressions are considered the main reasons for pit initiation. In addition, it was also confirmed that the twist angle of the turbine blade around its diagonal, is an important parameter that influences its WDE. Twist angle has an effect on: (a) impact angle, (b) erosion appearance, (c) impact speed, (d) affected area. Furthermore, according to the current experimental results, multi-ray rig erosion tests considered the closest simulation to the actual ex-service blade in terms of damage appearance.