Effect of residual stresses on the strength and endurance of surface-hardened parts

The authors present an evaluation of the most widely used methods of increasing the strength of equipment for the gas and oil industry thermochemical treatment and the application of a strengthening protective coating. In the process of surface hardening of parts, considerable residual technological stresses arise, and when they are added to the stresses induced by external forces, a complex state of stress is produced in the parts, which may considerably affect the strength and endurance of the parts involved. The strength and endurance of surface-hardened drilling pipes, pump bushings, plungers, glazed pump-compressor pipes and casings, etc., depend to a considerable extent on the magnitude and nature of the distribution of the residual stresses. However, in stress analysis and calculation of the wear resistance of these parts, the increased strength of the surface layers alone is taken into account as a rule. The effect of residual stresses on the strength and endurance of products is at present determined mainly experimentally.