Erosion Wear Behavior of Martensitic Stainless Steel Under the Hydro-Abrasive Condition of Hydropower Plants

The erosive wear of a hydraulic turbine due to suspended solid particles reduces its performance and service life. Martensitic stainless steel CA6NM, used for turbine parts of a hydropower plant, gets eroded heavily every year, particularly in the monsoon period. A high-speed slurry pot tester is employed to investigate the erosion behavior of the material under different operating conditions of practical interest. Scanning electron microscopy (SEM), as well as spark emission spectrometer (SES) and micro-hardness tester measurements, is used to investigate the erosion wear behavior of CA6NM. The impingement velocity is varied from 13 to 32 m/s for the particle size of 90.5-362.5 mu m and solid concentration of 500-4000 ppm at different orientation angles ranging from 15 degrees to 90 degrees. The erosion rate for suspension loading is increased with the increase in the impact velocity and particle size but decreased with an increase in suspension concentration. The index value in power-law relationship with erosion rate is found as 2.77 and 3.19 for velocity, and 1.42 and 0.97 for particle size for impingement angle of 30 degrees and 90 degrees, respectively. The micrographic analysis of the eroded sample is performed through a scanning electron microscope (SEM). At shallow impingement angle, the material loss dominantly occurred by micro-cutting and plowing, but at high impact velocity, some spackle of brittle failure is also observed. At large impingement angles, deep craters and crack formation are found responsible for the material loss under the present operating conditions.