Measures to Prevent Internal Leakage of Power Plant Valves

The following measures can avoid internal leakage of power plant valves:

1. Deepening understanding and holding someone responsible

Establish an organization to prevent internal leakage of valves; appoint a person responsible and strictly control valve maintenance and acceptance. Preventing internal leakage of valves is by no means a task which can be done by one or two dedicated workers, and it should be taken as an important task for power companies to ensure that the unit economy meets the standard. Professionals in the power generation and equipment department should establish a file for inspection and management of valves' internal leakage. In the overhaul of the unit, after the valve is overhauled, ground or repaired, professionals should press red lead powder to inspect the degree of bonding of the sealing surface. At the same time, a step-by-step acceptance system should be implemented. If the quality of maintenance is unqualified, it should be reworked firmly.
 

2. Periodic inspection

The purpose of regular inspection of thermal system valves is to monitor the development of internal leakage in valve operation, and to provide reliable data for closing the valve under pressure and repairing the valve after the system is shutdown. Periodic temperature measurement of the valve should be at least once a month. Periodic temperature measurement of the valve is divided into regular temperature measurement in operation, temperature measurement at the later stage after the valve is opened and working conditions change.
 
After the unit is started, the electric drain valve shall be manually closed once after the electric closing is completed. For valves with internal leakage, perform multiple temperature inspections and re-tightening after they are closed for 4 to 6 hours so that the valve may reach a tightly closed state. If the electric valve that is closed in normal operation of the unit is opened due to a change of operating modes or other abnormal reasons, it shall be manually closed once and checked after the system returns to normal.
 

3. Standard operation

When the unit starts or stops, choose the right time to close the valve. If the valve is closed too late or opened too early, the high temperature and high-pressure steam will cause serious scouring of the valve.

 

When valves are opened or closed, in principle shut-off valves can only be fully closed or fully opened, and these valves cannot be half opened or half closed to prevent the valve from being blown, causing internal leakage.

 

The opening and closing positions should be clearly marked for some butterfly valves on site. If these valves are closed well, you should stop turning. Otherwise, valves being closed too much will cause scouring of valves.

 

When valves with different models are opened or closed, you should select the wrench with the corresponding model or operate them by hands to prevent them from being damaged by improper force.

 

For electric valves which are not opened or closed automatically, close the valve to a certain place until it reaches the fully closed stroke so as to reduce or avoid the valve being damaged by improper force; the opening degree of the valve should not be reserved in principle.

 

For electric valves that open or close automatically, try to close them to a full closed stroke on condition that they can be automatically opened in any state.
 

4. Flushing after the system being stopped

Some valves are normally closed in operation. They are generally closed when they are opened after the system starts again. When the status of the valve changes, it is performed in the system without pressure. If impurities accumulate in the valve spool, it cannot be closed well. Therefore, these valves should be flushed under pressure several times when they are opened and closed, if conditions permit.
 

5. Adjusting the stroke of valves

The closing stroke of electric and pneumatic valves should be 0. Generally, the closing position of the valve is determined by torque. Make sure the valve can be closed well to prevent scouring.
 

6. Optimizing the thermal system

In order to prevent the internal leakage of the valve caused by the scouring of high-pressure steam, two gates are added to the system that requires throttle adjustment. Eliminate the repetitive design or rarely used drainage points to reduce the leakage points in the system valves, such as the repeated design of the water supply system drainage and air discharged points, the first and second ventilation valves of the steam turbine. Add a manual gate behind the medium and high pressure steam trap pneumatic gate, and keep the manual door fully opened in the process of testing.
 
Conclusion
Controlling internal valve leakage of the thermal system is the basic work for coal-fired power plant units to reduce heat consumption and improve economy. Equipment managers doing a good job in valve internal leakage control and maintenance, correct operation of operation personnel and timely inspection of internal leakage of valves are the main methods to reduce or eliminate leakages of valves. The internal leakage of valves can be greatly improved as long as there are enough attention, preventive measures, proper operation and maintenance.