Diagnosis and remedial measures for internal leakage in thermal power plant valves
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Valves in thermal systems are mainly classified into globe valves, gate valves, butterfly valves, control valves, safety valves, etc. They play roles such as controlling the flow direction of the medium, isolating or connecting different systems, regulating flow rates, and ensuring the safe operation of the system. Internal leakage in valves inevitably leads to steam and water loss, resulting in energy losses. This forces an increase in the amount of water that needs to be supplied to the system, and consequently more coal must be used as well. Additionally, corrosion caused by internal leakage reduces the lifespan of the valves, accelerating their wear and damage. This not only affects the company’s economic efficiency but also undermines the safety of the equipment. Internal leakage of valves is a common problem in many power plants, and preventing such leakage is an important measure for thermal power plants to achieve energy conservation and emission reduction.
I. Diagnosis methods for internal valve leakage: Manual observation method: Drain water until the system is at zero pressure, and observe whether pressurized water continues to flow out of the drainage funnel after the valve is closed. Use a copper listening rod placed at the valve to check for any signs of leakage. Temperature determination method: For high-temperature valves, after closing them for 6 to 8 hours, use an infrared thermometer to measure the temperature of the metal at a distance of 100 mm to 150 mm downstream from the valve stem or valve body; if this temperature is greater than 70°C, it is considered that there is an internal leak. Low-temperature valves: If the temperature behind the valve is lower than the ambient temperature after it is closed, or even frost forms, it is considered to be leaking internally. Method of changing the system operation mode: By altering the way the system operates, it is possible to observe changes in parameters such as pressure and flow at the valve, thereby determining whether there is any internal leakage in the valve. II. Measures to address internal leakage in valves: Select qualified steam traps: When purchasing steam traps, it is necessary to choose reliable suppliers and verify the tightness of these traps at regular intervals. Strengthen the responsibilities for inspection and acceptance: Establish an organizational structure to prevent internal leakage in valves, assign responsible persons to ensure compliance with relevant standards, and maintain records for the inspection and correction of such leaks. After valve maintenance, grinding, or repair, a professional should inspect the degree of fit between the sealing surfaces; if the quality of the maintenance is not satisfactory, rework must be carried out. Install tube wall temperature sensors: Tube wall temperature sensors shall be installed on the outer walls of the pipes before and after the drain valve, and connected to the DCS system, to facilitate real-time monitoring and management of any internal leaks in the drain valve. Valve repair and maintenance: Regularly inspect, repair, and maintain valves to prevent the accumulation of iron oxide rust and other debris inside them, which could prevent the valves from opening and closing properly and lead to internal leakage. Other precautions: Ensure that steps such as hydrostatic testing, cleaning, drying, and lubrication before valve installation are carried out strictly. When installing the flanged gate, the fasteners must be tightened in a symmetrical sequence to ensure sealing. During the installation of valves, they must be installed correctly according to the system and pressure requirements; random or mixed installation is strictly prohibited.