An Analysis of the Causes of Valve Leakage and Preventive Measures

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In a piping system, which serves as a carrier for fluids, it is necessary to control factors such as the flow rate, pressure, and direction of the fluid. The devices used for this purpose are valves. As an important component of piping systems, valves play a crucial role in managing gases, liquids, gas-liquid mixtures, or solid-liquid mixtures that flow within the pipes. Typically, a valve consists of a valve cover, valve body, valve seat, actuating mechanism, moving part, sealing elements, and fasteners. It possesses excellent sealing performance, strength, adjustability, operational performance, and flow properties. Observations from the long-term use of valves show that leaks typically occur in the packing seal, the valve body, and the flanges. The hazards caused by valve leaks are extremely serious; when a valve leaks, it can lead to fires, explosions, and injuries. It also reduces the lifespan of the equipment, prevents companies from carrying out their production activities properly, and results in an increase in unplanned shutdowns, thereby severely damaging the economic performance of the company. Therefore, it is necessary to analyze the causes of valve leaks in order to find effective solutions that ensure the safe operation of valves and help create positive economic and social benefits for the company. 　　1. Analysis of the reasons for valve leakage 　　1.1 Quality issues with the valve itself. 　　The parts of the valve that are prone to quality issues can be divided into two categories: the surface and the internal components. Since valves are used to control the flow of fluids in pipeline systems, they have numerous sealing elements. Before installation, any quality problems on the exterior of the valve—such as surface scratches, cracks, rust, or deformation of the flanges—can be easily detected with the naked eye, allowing for timely correction. However, its internal quality issues are difficult to detect, and these are the main causes of valve leakage, such as internal sand holes, slag inclusions, bubbles, welding defects, or problems related to improper material selection, unreasonable design, inadequate heat treatment, and loose connections. The existence of these problems can cause the valve to be damaged prematurely or to leak under the influence of the fluid during use. 　　1.2 Erosion of the internal medium causes damage to the sealing surface. 　　During operation, as the fluid inside the valve flows through the pipes, it exerts a scouring and cavitation effect on the valve’s sealing surfaces. Under continuous scouring and cavitation, these sealing surfaces are prone to local damage; coupled with chemical erosion, all these factors combined affect the sealing surfaces, making the valve highly susceptible to damage as a result of erosion, which can lead to leaks or even complete failure of the valve. 1.3 Damage caused by improper selection and poor operation. 　　When selecting valves, it is necessary to choose them based on the specific operating conditions; an improper selection may result in poor sealing, leading to internal leaks. It is also important to understand the differences and functions of various valves in order to reduce erosion and wear on the sealing surfaces. Additionally, improper handling during valve installation, as well as inadequate quality control measures during installation, can also lead to valve leakage. During maintenance, it is essential to prevent sand, slag, metal shavings, and similar substances from entering the valve chamber; once such impurities get inside, they can have a severe impact on the sealing performance of the valve. 　　1.4 There are issues with the design and manufacturing quality. 　　If there are excessive errors during the valve manufacturing process, the valve disc and seat may not be aligned properly, and the sealing surfaces may not fit together perfectly, resulting in leaks. Poor processing of the sealing surface is characterized by defects such as cracks, pores, and inclusions on its surface; this is caused by improper selection of materials for surfacing and heat treatment, or by inadequate execution of these processes. Incorrect material selection or improper heat treatment can result in either too high or too low hardness of the sealing surface, ultimately leading to uneven hardness and reduced resistance to erosion. Materials of the sealing surfaces of the valve disc and seat that do not meet the requirements, insufficient machining precision, mismatched wedge angles of the valve disc and seat in gate valves, as well as uneven widths of the sealing surfaces leading to poor fit, can all cause issues such as the valve disc not being in position or the valve not being able to close properly. 　　2. Main measures to prevent leakage 　　2.1 Select appropriate materials to reduce the occurrence of corrosion. 　　As a carrier for the medium, valves are greatly affected by the corrosiveness of that medium, which can lead to leaks. Corrosion affects different materials based on their chemical and physical properties, and in all cases, such corrosion results in damage to the valve, thereby causing leaks. Therefore, during the use of valves, anti-corrosion measures should be taken first; different valve materials should be selected depending on the medium they are intended to handle, in order to enhance their corrosion resistance. The corrosive effect of the medium on valves is directly related to the concentration, temperature, and pressure of the medium; an increase in the temperature, concentration, and pressure of the medium accelerates corrosion. Due to the varying degrees of corrosivity caused by different media, which exhibit highly complex characteristics, it is necessary to analyze the corrosive factors in specific situations when selecting valve materials, in order to choose the appropriate material. 　　2.2 Appropriate opening and closing force to prevent damage to the sealing surface. 　　In actual piping systems, manual valves that operate at normal temperature and pressure are widely used. Such valves are designed to be operated using human strength via their handwheels and handles; therefore, they can only be operated by hand and not with a wrench. Because if a wrench is used for the operation, it can easily cause damage to the valve stem threads, which in turn leads to failure in opening and closing the valve and results in accidents. At the same time, care must be taken when operating by controlling the amount of force applied, to avoid damaging the handwheel or handle. Additionally, if the handwheel or handle is damaged or lost, it should be replaced immediately, and the use of wrenches must be strictly avoided. 　　2.3 Operate the valves correctly to prevent damage to them. 　　For high-temperature and high-pressure valves, they should be pre-heated before being opened, and any condensed water must be removed ； When turning it on, do so as slowly as possible to avoid water hammer. After the valve is fully opened, turn the handwheel slightly in the opposite direction to ensure a tight fit between the threads, thereby preventing loosening and damage. For straight-stem valves, remember the position of the stem when the valve is fully open or fully closed, to avoid hitting the dead center when it is fully open. If the valve disc falls off or debris gets trapped between the valve core seals, the position of the valve stem when the valve is fully closed will change. When the valve is first turned on, there are certain impurities in the pipeline. The valve can be opened slightly to allow the high-speed flow of the medium to carry away these impurities; after that, the valve is closed and then opened again. This process is repeated several times to remove all the impurities. For normally open valves, debris may stick to the sealing surface; therefore, it should be cleaned thoroughly several times before closing them. Cooling of the medium after the valve is closed causes the valve disc to contract, so the operator should close it again at an appropriate time to ensure no gaps remain in the sealing surface. 　　2.4 Pay attention to the flow direction of the medium through the valve to prevent it from failing. 　　For valves such as stop valves, throttle valves, pressure reducing valves, and check valves, the flow direction of the medium is fixed, and these valves are equipped with permanent flow direction indicators on their bodies. Like throttle valves, installing them in the wrong orientation will affect their performance and lifespan ； If the pressure relief valve is installed in the wrong orientation, it will not function at all ； For check valves, installing them in the reverse direction can pose serious dangers. In accordance with relevant standard requirements, valves must all have direction indicators on their bodies ； In the event that it is not available, it should still be correctly identified based on the basic principles of valves. 　　2.5 Install valves correctly to extend their lifespan. 　　For high-temperature valves, since they are installed at room temperature, the gap increases as the temperature rises during normal operation; therefore, they must be tightened again, otherwise leakage is likely to occur. When the valve is put into use, the packing should not be compressed too tightly – sufficient tightness to prevent leakage is sufficient. This is to avoid excessive pressure on the valve stem, which could accelerate wear and make it difficult to open and close the valve. The gate valve must not be installed in an inverted position, with the handwheel facing downward; otherwise, the medium will remain inside the valve cover for an extended period, which can lead to corrosion of the valve stem. It also makes it very inconvenient for operators to replace the packing. During installation, care must be taken to prevent the valve from being subjected to strong gravitational forces. Before installation, the valve should be inspected to verify its specifications and model, and to check for any damage, especially to the valve stem. It is necessary to turn it a few times to see if there is any misalignment, as the valve stem is prone to damage during transportation. During installation, iron oxide particles, sediment, slag, and other debris should be blown away using compressed air. To prevent it from scratching the sealing surface of the valve, as this could even block valves with smaller passageways and render them ineffective. 　　3. Conclusion 　In summary, based on the analysis of the causes of valve leakage, relevant organizations should strengthen the implementation of measures to prevent leakage in valves. Strict quality control is maintained by obtaining detailed information about the media used by users, enabling valve manufacturers to make timely adjustments to the design of valves based on this information, thereby ensuring the quality of the valves. Before use, the quality of the valves must be carefully checked, and the installation and operation procedures must be followed strictly. Pressure testing should be carried out first, and any issues found should be addressed by replacing the valves promptly. Strengthen the daily management of valves, establish a comprehensive system for their regular inspection, operate and maintain them in strict accordance with established procedures, and conduct periodic checks to ensure their optimal performance, extend their service life, prevent leaks, and address potential issues before they arise.