Failure Analysis on Cracking of Equalizing Valve Disc of a Medium-Pressure Adjustment Valve

The chemical compositions, microstructure, mechanical properties, and macroscopic and microscopic fracture morphology of an equalizing valve disc were analyzed by using channel alloy analyzer, optical microscope, tensile and impact testing machines, and scanning electron microscope. And the cracking causes of the equalizing valve disc were analyzed in combination with the site conditions. The results show that due to the poor toughness and plasticity of the equalizing valve disc, brittle cracking happened at the contact position with the anti-rotating pin where there was a large expansion force. Cracks originated from the center of the inner surface of the valve disc in contact with the anti-rotating pin, and the dense cavities in the material connected to form the initial micro-cracks. The carbides precipitating at the grain boundaries deteriorated the overall crack propagation resistance of the material, so the cracks expanded rapidly and connected to each other to form large cracks, which eventually caused the valve disc to crack.