Analysis of the causes of gate valve leakage and treatment measures

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Gate valves are the most common type of industrial valve, widely used in industries such as petroleum, petrochemicals, power plants, long-distance pipelines, and shipbuilding. As a fluid control device, the operating element of a gate valve is a gate plate; through the upward and downward movement of this gate plate, the valve switches between its open and closed states, thereby enabling the isolation or connection of the medium in the pipeline. If a gate valve leaks, it can easily pose risks to pipelines and equipment, and may even affect the safety of personnel and the integrity of the equipment. Understanding the structure and operating principles of gate valves can help us operate them correctly and better understand their operational status. Once a gate valve starts leaking, it is possible to take the right actions promptly, thereby reducing economic losses and minimizing the likelihood of accidents. Gate valve leakage is generally divided into internal leakage and external leakage. There are many reasons that can cause gate valve leakage, and in-depth analysis and research are required before appropriate corrective measures can be taken. 1. Reasons for gate valve leakage 　　 1.1 Low machining precision of the wedge-shaped seal ring leads to internal leakage in the valve. 　　 Wedge-shaped seals can be divided into two categories: the first is a hard seal, also known as a metal wedge ring; the second is a soft seal, also known as a composite graphite wedge ring. If the precision of the wedge-shaped sealing ring is low, it can easily cause internal leakage in the gate valve. 1.2 Unstable operating conditions during production lead to internal leakage in the gate valve. The unstable conditions during the valve’s production process can result in significant fluctuations in pressure and ambient temperature, which puts considerable stress, erosion forces, and deformation on the sealing ring. This leads to an increasing gap between the sealing ring and the valve body, thereby causing internal leakage in the valve. 1.3 Poor quality of valve maintenance leads to internal leakage in the gate valve. During the maintenance process, when installing the wedge-shaped seal ring, the sealing surface was not cleaned properly; small particles and impurities remained on it. These impurities can scratch the sealing surface as the valve operates, and if such scratches become penetrating, they will cause the valve to leak. 1.4 Corrosion of the wedge-shaped sealing ring by the medium causes internal leakage in the gate valve. When designing the wedge-shaped sealing ring, special attention must be paid to its strength and corrosion resistance; the surface hardness of this ring should be lower than that of the sealing layer on the valve cover, and it must be able to undergo plastic deformation under external forces. Over time, the medium can also corrode the wedge-shaped sealing ring, leading to leakage in the gate valve. 1.5 Internal leakage in the gate valve caused by improper operation of the valve actuator The opening and closing of the gate valve are controlled by the actuator, which relies on liquids, gases, electricity, or other forms of energy; through motors, cylinders, or other devices, this energy is converted into a driving force that moves the valve to its fully open or fully closed position. If the actuator does not open or close properly, it will prevent the gate valve from opening or closing completely, resulting in internal leakage of the valve. 1.6 Valve body defects causing external leakage of the valve Cast valve bodies often suffer from casting defects such as pores, inclusions, cracks, and sand holes. If these defects are not detected in the factory, or if no proper repair measures are taken once they are discovered, external leakage of the valve will occur during its use in the field. 2. Measures for dealing with gate valve leaks 　　 2.1 Securing the valve body plate and increasing bolt tension 　　 When there is a leak or a minor leakage in a gate valve, the first step is to tighten and secure the valve body plate. By increasing the tension of the bolts, the pressure between the plate and the wedge-shaped seal ring is enhanced, which helps to cause plastic deformation of the seal ring. This in turn reduces the gap between the valve body, the plate, and the seal ring, thereby preventing leaks due to the valve’s self-sealing mechanism. If the leakage rate does not change significantly while tightening and securing the bolts, the tightening process must be stopped immediately, and alternative measures should be taken instead. 2.2 Injecting sealant through the grease injection hole 　　 When there is a slight internal leakage in the valve, sealant can be injected into the sealing surface or packing through the grease injection hole to temporarily alleviate the internal leakage. When it is convenient for inspection and maintenance, the valve can be removed and sent back to the factory for repair. 2.3 Welding to fill the gaps between the valve body end face, the packing box, and the pressure plate. To address self-sealing leaks in the valve, it is necessary to remove the valve handwheel and the valve frame. First, it is important to work together with the technicians to understand and adjust the conditions at the site; after the valve is fully opened, the bolts fixing the valve frame are removed. Once it is confirmed that the valve stem is not moving up or down by rotating the valve frame, the valve frame itself can then be removed. After removing the valve frame, it is necessary to expose the valve body at the area of the valve’s pressure plate; moreover, the gap between the pressure plate and the valve body must be sealed and welded. To facilitate the reinstallation of the valve frame after sealing any leakage points, the width of the weld seam should be between 5 millimeters and 8 millimeters. The angle between the weld corners and the pressure plate should be 45 degrees, with any necessary adjustments made based on the actual assembly conditions. 2.4 Check the zero position of the actuator 　　 The zero position setting of the actuator is inaccurate, and the valve does not reach its fully closed position. By manually opening and closing the valve, and then adjusting the zero position of the actuator, ensure that the actuator can open or close the valve completely and accurately. 2.5 Welding repairs on the valve body or return to the manufacturer for repair 　　 When leakage occurs in the valve body, the valve manufacturer can carry out welding repairs to fix the defects, or the valve can be sent back to the manufacturer for repair and replacement of the valve body. First, it is necessary to assess the defects present in the valve body. Penetrating cracks, through-holes, and shrinkage areas exceeding a certain size cannot be repaired; in such cases, the valve body must be sent back to the manufacturer for replacement. For valve body defects that can be repaired by welding, an appropriate welding process must be developed, including the welding method, electrode material, and method for relieving stress after welding; furthermore, appropriate non-destructive testing should be carried out on the welded areas to ensure that the repairs meet the required standards. 3. Conclusion 　　 By analyzing the causes of gate valve leakage and the corresponding treatment measures, it is possible to alleviate or eliminate valve leakage through approaches such as increasing bolt preload, performing on-line sealing under pressure, and injecting sealants. Pressurized plugging should be carried out by personnel with a solid professional foundation; methods such as welding to reinforce the gaps at the end face of the plug valve, in the packing box, and around the pressure plates, as well as the injection of sealant, can effectively prevent leakage incidents, thus providing guidance and reference for addressing similar valve leakage problems.