What are the phenomena of water hammer in steam turbines?

The main hazards are as follows: 1. Scratching between moving and stationary parts. When water or cold steam enters the turbine, the metal components that are at high temperatures cool down suddenly, resulting in rapid contraction. This generates significant thermal stress and thermal deformation, leading to sharp changes in relative expansion. As a result, the unit vibrates intensely, and there is scratching between the moving and stationary parts in both axial and radial directions. Severe radial rubbing can lead to major shaft bending accidents. 2. Blade damage and fracture: When a large amount of water enters the flow passage of the turbine, it can cause damage to and fracture of the blades, especially those that are longer. 3. Burnout of the thrust bearings: 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. The absolute velocity of the fluid exiting the nozzle is much lower than that of the steam, which means that the angle at which this fluid enters the rotor blades is much larger than the angle at which steam enters those blades. Consequently, the fluid flow does not enter the rotor blade channels in the correct direction, and instead impacts the back arc of the inlet side of the rotor blades. In addition to exerting a braking force on the moving blades, this also generates an axial force that increases the axial thrust of the turbine. In actual operation, the axial thrust can even increase to 10 times that under normal conditions, causing the thrust bearings to be overloaded and resulting in the burnout of the bearing components. 4. Steam leakage at the valve or cylinder joint: If the valve and cylinder are cooled rapidly, it can cause permanent deformation of the metal, resulting in steam leakage at the valve or cylinder joint. 5. Induction of metal cracks: During the start-up and shutdown of the unit, if water or cold steam enters frequently, the metal will develop cracks under the effect of repeated alternating thermal stresses. If the rotor surface at the steam seal is repeatedly and rapidly cooled by water or cold steam from the steam seal supply system, cracks will form and continue to widen.

The most obvious phenomenon is abnormal shafting vibration of the unit.