Experimental assessment of droplet impact erosion of low pressure steam turbine blades

The erosion of last stage steam turbine blades is a common problem for the steam turbine manufacturing industry and power utility community. This type of erosion is related to water droplet impact associated with the condensation of steam in the lower pressure stages of steam turbines. Although several changes both in the steam turbine stage design and steam properties have been adopted to eliminate this problem, none of them have proved to eradicate this phenomenon completely. The only option left for the scientists and designers is to mitigate the process by utilising materials with high erosion resistance. This requires the development of high erosion resistive materials and then quantitative confirmation of their erosion resistance by using some precise and accurate laboratory methods reflecting the conditions in the last stages of steam turbines. The Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM), University of Stuttgart has the capability to assess the erosion resistance of materials in an erosion test rig which simulates the conditions in the last stages of steam turbines. Different steam turbine blading materials have been tested in the erosion test rig at different testing conditions by using a standard button-type specimen. The effect of the most prominent parameters like impact speed and impact angle has been measured and analysed. The erosion course has been studied by long-term testing of the materials to identify different erosion stages. The resistance against erosion of steel and titanium has been assessed and shown to be related to different macro properties. For a more effective blade shielding concept, different surface treatment methods have been suggested and analysed in the erosion test rig.