A Study of Droplet Erosion on Two L-0 Turbine Stages

Water droplet erosion continues to pose a serious potential threat to the critical path of maintenance outages. Despite advances in techniques and processes to mitigate erosion, combined cycle arrangements still result in an unexpected level of wetness within the steam, which can produce extensive damage to the last stage blade rows. A procedure is discussed that has been used successfully to manage the critical reliability issues that are raised once conditions of water droplet erosion are found. Erosion rate is estimated from (1) empirical models obtained from the literature, (2) for the steam flow conditions specific to the unit, and (3) with stresses obtained from analysis of the damaged blades. Two applications are presented to demonstrate how the erosion rates were used to provide a basis for two very different strategies, both of which were able to avoid the prohibitive cost of extending the immediate outage to obtain and install new replacement rows.