Simulation of pitting corrosion on gas turbine compressor blade

First row rotating blades of four axial-flow compressors were prematurely fractured. Previous investigations showed that the site atmosphere contains corrosive compounds which lead to an increase in possibility of pitting on the blades. To this end, experimental and numerical studies are considered. Replica testing, Scanning Electron Microscope (SEM) and fractography of the broken blade indicate that the pits join together and make one bigger pit under SCC mechanism which reduces the failure time. 3-D models of the pitting on the blade under existing forces are analyzed by COMSOL Multiphisics software. The simulation results show the location of maximum stress concentration inside one of the pits which is compatible with the location of initial SCC crack in the pit depth. Finite element analysis shows good similarities with fractography photos. Stress concentration and interaction of stresses around the pits are two mechanical reasons for initiation and growth of cracks. Calculations show that the occurrence of SCC at the location of the pit reduces the crack initiation time to half. The presence of pits increased the stress by approximately 130 MPa relative to the healthy blade. The part between the two pits with a stress of approximately 180 MPa showed the interaction of the two pits in the operating conditions of the compressor blade.