Failure analysis and factors influencing spline wear in hydraulic motors of charging pumps in nuclear power plants

Abstract

Metallographic analysis techniques such as optical microscopy and scanning electron microscopy were used to observe the morphology of spline wear, confirming the presence of fretting wear characteristics. Microstructural analysis of spline cross sections using a metallographic microscope revealed surface carburization treatment on the splines. Hardness tests conducted from the surface to the core of the splines showed a gradual decrease in hardness, consistent with the observed microstructural features. The chemical composition of the spline was analyzed using a spectrometer, and the main component content was analyzed.By combining finite element analysis techniques, this study analyzed the effects of factors such as forces, eccentricity, and lubrication on spline wear. The results indicated that the varying degrees of spline wear in the hydraulic motors of charging pumps in the on-site conditions of the nuclear power plant were primarily attributed to differences in spline eccentricity after manufacture and assembly. Further investigation revealed that the fundamental cause of spline wear in hydraulic motors was the operation of the equipment under conditions deviating from the rated operating points, resulting in poor circulation of oil within the motors and insufficient spline lubrication. Specifically, operating the equipment at lower pressures and away from the rated operating points resulted in reduced oil flow velocity, increasing the friction between the spline mating surfaces. The poor lubrication of the spline and eccentricity are the primary reasons for spline wear, and the combination of these two factors exacerbates spline wear. To address the wear issue of the hydraulic motor, we replaced it with a linear-axis hydraulic motor and conducted a comprehensive analysis of the linear-axis hydraulic motor. The results indicate that the linear-axis hydraulic motor can effectively reduce wear, and after testing at the nuclear power plant, it meets the operational time requirements on-site.These findings offer valuable guidance for the maintenance and operation of charging pumps in nuclear power plants, facilitating the prevention of similar issues and enhancing equipment reliability and operational efficiency.