Causes of Medium-Pressure Control Valve Failure in Power Plant Turbines

In power systems, the steam turbine is the core equipment for power generation. Its efficient and stable operation has a crucial impact on the safe and reliable power supply of the entire system. Among the various control components, the performance of the medium-pressure control valve directly affects the operating efficiency and safety of the steam turbine. The main function of the medium-pressure control valve is to adjust the steam flow through the turbine to match load demands and maintain stable operation of the generator. Therefore, in-depth research into the causes of medium-pressure control valve failures and the exploration of effective treatment technologies are crucial for improving the operational efficiency and reliability of power plants.
 

The role of the medium-pressure control valve in the steam turbine system is to accurately control steam flow to the turbine, adapting to changes in grid load and optimizing the turbine’s operation. The valve body design of the medium-pressure control valve must ensure stable and efficient fluid dynamic characteristics in a high-temperature, high-pressure working environment. The valve body is usually made from high-temperature and corrosion-resistant alloys to withstand long-term thermal and mechanical stress. The flow channel design inside the valve body needs to optimize steam flow characteristics, reduce turbulence and flow resistance, and improve the overall thermal efficiency of the system. The driving mechanism of the medium-pressure control valve includes electric, pneumatic, or hydraulic actuators, responsible for converting control signals into the physical movement of the valve. When selecting the driving mechanism, response speed, accuracy, and reliability must be considered. For example, electric actuators offer higher control accuracy and are convenient for remote control, while pneumatic or hydraulic actuators deliver faster response and stronger driving force in certain applications. The control system is essential for the function of the medium-pressure control valve. It receives signals from the turbine control system, such as load demand, steam pressure, and temperature, and calculates the optimal valve opening based on this information. Additionally, modern medium-pressure control valve systems may integrate intelligent algorithms and data analysis functions to optimize performance adjustment and enable fault prediction.
 
The feedback mechanism plays a critical role in ensuring the valve position matches the control signal. It is typically implemented through position sensors, such as rotary encoders or linear displacement sensors, which monitor the valve's actual position in real time and send this information back to the control system. This closed-loop control mechanism ensures that the valve can continue to accurately regulate steam flow, even with changing external conditions or internal wear.
 

Mechanical failure not only affects valve performance but may also reduce the efficiency and increase safety risks of the entire turbine system. Wear and corrosion are among the most common mechanical failures of medium-pressure control valves. In high-temperature and high-pressure environments, valve components are often subjected to continuous friction and impact, resulting in material wear. Additionally, impurities and chemicals in the steam may corrode valve components, further accelerating wear. This wear and corrosion not only reduce the valve’s sealing and regulation accuracy but may also cause leakage, impacting the system's overall efficiency and safety. Seal failure is another major cause of mechanical failure. The control valve’s sealing performance is essential for maintaining proper steam flow and pressure. However, prolonged exposure to high temperature, pressure, and chemical corrosion can cause the sealing material to age, harden, or deform, leading to seal failure. Seal failure not only causes steam leakage and increased energy loss but may also lead to unstable and inaccurate valve control, thus impacting the turbine's overall operating performance.
 

Operation errors not only affect valve performance but may also reduce the efficiency and increase safety risks of the entire turbine system. Improper operation is a leading cause of medium-pressure control valve failure. In practice, operators may make incorrect decisions due to inadequate training or inexperience. For example, improper control of valve opening and closing speed and degree may cause excessive wear or damage to valve components, especially when responding to sharp changes in grid load. Additionally, improper operator actions during maintenance and overhaul, such as using inappropriate tools or methods, may cause damage to valve components or reduce performance. Thus, ensuring that operators receive proper training and understand the correct operation and maintenance procedures for medium-pressure control valves is crucial to preventing errors. Control system failure is another significant factor contributing to medium-pressure control valve operation errors. The control system of a medium-pressure control valve typically includes sensors, controllers, and actuators. Failure of these components may send incorrect control signals to the valve, leading to improper operation. Thus, regular inspection and maintenance of control system components to ensure their accuracy and reliability are essential to avoiding operation errors.
 

Environmental factors profoundly impact the performance and service life of control valves and cannot be ignored during actual operation. Control valves operate in extremely harsh environments within power plant turbines and often face challenges of high temperature and pressure. High temperatures accelerate the oxidation and softening of metal materials, reducing their mechanical strength and corrosion resistance, while high pressure can cause material stress to exceed limits, leading to cracks or fractures. Therefore, these environmental factors must be considered when designing control valves, and appropriate materials and designs must be chosen to withstand high temperature and pressure environments. Chemical corrosion and deposit issues cannot be ignored. During power plant turbine operation, steam may contain various chemicals, such as chlorides, sulfides, and other corrosive substances. As steam flows, solid particles and other deposits may accumulate inside the valve, leading to flow channel blockage, increased wear, and even jamming of moving parts. Therefore, the design and maintenance strategy for control valves must consider reducing the impact of chemical corrosion and preventing the accumulation of deposits.