What are the hazards of water hammer in steam turbines?

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The hazards of water hammer in steam turbines include: (1) friction and impact between moving and stationary parts. The introduction of cold water or cold steam into the turbine causes the metal components, which are at high temperature, to cool down suddenly and contract rapidly, resulting in significant thermal deformation and a sharp change in relative expansion, which in turn causes intense vibrations in the unit. Axial and radial friction and impact occur between the moving and stationary parts; large shaft bending is generated during radial friction and impact. (2) Damage and breakage of leaves. When a large amount of water enters the flow passage of the turbine, it causes damage and breakage to the blades, especially those that are longer. (3) The thrust bearing is burned out. The density of the water or cold steam entering the turbine is much greater than that of the steam; as a result, the same acceleration as that of the steam cannot be achieved within the nozzle. This causes the inlet angle of the relative velocity of this fluid to be much larger than that of the steam, preventing the flow from entering the flow channel in the correct direction and leading to impacts on the back arc at the inlet of the moving blades. In addition to generating a braking force on the moving blades, this also creates an axial thrust, thereby increasing the axial thrust of the turbine. In actual operation, the axial thrust of the turbine can increase to 10 times that during normal operation. Overloading the thrust bearing causes the tungsten alloy to burn out. (4) Steam leakage at the joint of the valve or cylinder. If valves and cylinders are cooled rapidly, it can cause permanent deformation of the metal. It causes steam leakage at the joint surface of the valve or cylinder. (5) Causes metal cracks. During the start-up and shutdown of the unit, if cold water or cold steam enters frequently, the metal may develop cracks under the effect of repeated alternating thermal stresses. If the rotor surface at the steam seal is repeatedly cooled by water or cold steam from the steam seal supply system, cracks will form and continue to widen.