The sealing surface of a flanged end gate valve is the core component that ensures the valve closes tightly without leakage. After long-term use, the flanged end gate valve's sealing surface is easily scoured by the medium in the pipeline, abraded by impurities, and impacted by the force when opening and closing the valve, resulting in wear problems such as scratches, grooves, and small pits. This, in turn, causes medium leakage and affects the safe operation of the entire pipeline system. Therefore, when repairing, you must first accurately judge the severity of the wear, then select the corresponding repair method according to the situation. You also need to pay attention to the coaxiality of the flange connection throughout the process to ensure that the flanged end gate valve can seal well and be assembled accurately after repair.
1. Judgment of Wear Severity
Before repairing the flanged end gate valve, you need to use professional tools to judge the wear level first: Mild wear means there are only fine scratches on the sealing surface, no obvious grooves, the wear depth is less than 0.5 mm, and the flatness deviation does not exceed 0.03 mm; Moderate wear will have local grooves, the wear depth is between 0.5 and 1.5 mm, the flatness deviation is 0.03 to 0.1 mm, and the sealing fit effect of the flanged end gate valve will also deteriorate; Severe wear means the grooves run through the entire sealing surface or there are local depressions, the wear depth exceeds 1.5 mm, and it is often accompanied by serious problems such as deformation and spalling of the flanged end gate valve's sealing surface.
2. Graded Repair Processes
1. Mild wear: You can repair the flanged end gate valve directly by grinding. First, thoroughly clean the sealing surface to remove any oil stains, impurities, and rust. Next, choose an abrasive that is suitable for the material of the sealing surface. Start with a coarse abrasive to eliminate surface scratches, then switch to a fine abrasive to achieve a smoother finish. Finally, grind the surface until it reaches a roughness of Ra ≤ 0.4 μm. After completing the repair, use the light transmission method to check that the sealing surface fits evenly without any gaps that allow light to pass through. Then, perform a water pressure test on the flanged end gate valve. If there are no leaks, the valve is considered qualified.
2. Moderate wear: You need to use the combined method of "surfacing + precision machining" for the flanged end gate valve. First, remove the flanged end gate valve from the pipeline, use a lathe to cut off the wear layer and fatigue layer, preheat the valve body, then use argon arc welding to perform segmental and symmetrical surfacing with wear-resistant electrodes. It is crucial to control the interpass temperature, which should not exceed 150°C, cracks are likely to occur. After surfacing, perform stress relief heat treatment, then use a lathe or grinder to restore the dimensional accuracy of the sealing surface, and finally perform fine grinding to improve the sealing fit effect.
3. Severe wear: The sealing surface components must be replaced. If it is an inlaid sealing surface, directly remove the old sealing ring and replace it with a new one of the same specification as the original; if it is an integral sealing surface, use the patch welding method to cut off the damaged area, weld a new base material block, then perform lathe processing and grinding in accordance with standard processing procedures to ensure that the fit rate with the valve disc sealing surface is not less than 95%.
3. Assembly and Acceptance After Repair
When assembling the flanged end gate valve after repair, focus on calibrating the coaxiality of the flange and the sealing surface, and the deviation should not exceed 0.02 mm to avoid uneven stress. Then conduct a water pressure sealing test on the flanged end gate valve at 1.1 times the nominal pressure of the valve, and maintain the pressure for 15 to 30 minutes. If there is no obvious leakage, it means the acceptance is qualified. After qualification, apply a layer of anti-rust oil on the sealing surface and then a protective film to prevent damage to the flanged end gate valve during transportation and storage.
4. Notes
Here are a few key points to note: The valve body must be preheated before surfacing; do not weld directly in the cold state, otherwise it is easy to cause the valve body to crack; clean the residual abrasive in time during grinding to avoid particle impurities scratching the sealing surface again; all data during the repair process should be recorded in detail and stored in the equipment maintenance file for reference in subsequent operation and maintenance.
