Study of pitting corrosion under actual operating conditions of a first stage compressor blade. (January 2022) - Mollapour, Yousef
Highlights: The pit tends to develop on the surface. This means that the surface development of the pit is greater than the development in depth. This is because there are more chemical reactions and corrosion in the areas near the pit surface. On the other hand, according to the simulation results, the chloride ion concentration decreases with the progression of the pit depth. Some products such as FeCl +, FeCl2, etc. form around the pit opening, and fewer chlorine ions reach the depth. Stress concentration and stress interaction around the pits are the two mechanical reasons for the development of the pits towards each other. Under corrosion, the pits join together and form an equivalent pit. The presence of the pits caused a stress increase of about 130 MPa compared to the blade without pits. The area between the two pits with stress of about 180 MPa showed the interaction between the two pits in the operating conditions of the compressor blade. An equation was presented based on the simulation results and the actual operating conditions of the blades. The simulation and estimation of the surface conditions of the compressor blade lead the gas turbine operator to make the necessary decisions before irreparable accidents occur. The simulation was performed for 48 months on a compressor blade with pits. There was a good agreement between the simulation results and the results from the turbomachinery laboratory of the Texas A&M University. Abstract: In this study, pitting corrosion was investigated numerically and experimentally under actual operational conditions of a gas turbine compressor. First, the samples cut from a blade made of Custom 450 stainless steel were exposed to different corrosion times in a 3.5 wt% NaCl solution. After the creation of pits in the samples, the dimensions of the corrosion pits were measured using a 3D profilometer device. The stoichiometry equations governing the corrosion of the Custom 450 alloy in a chloride solution were extracted and applied to the models. The results of this simulation were validated by comparing the depth of the simulated pits and the experimental samples. Subsequently, simulation was conducted for 48 months on a compressor having pits. There is a good agreement between the simulation results and the results obtained from the Turbo machine laboratory of the Texas A&M University. In addition, pits grew under the influence of corrosion, joined together, and made an equivalent pit.