Measures for Internal Leakage of Ball Valves
Feb 05, 2024
As the opening and closing parts for fluids in natural gas pipelines, ball valves have been widely used in China-Myanmar and Guangnan natural gas stations. However, internal leakage of valves occurs from time to time due to manufacturing, transportation, construction and installation, operation and maintenance, which seriously affects the service life of the valve. The causes of internal leakage of ball valves are analyzed, corresponding measures are taken and a standard process for dealing with internal leakage of ball valves was put forward in this article.
2.2.5 Repairing internal leakages of valves
The processes of valve internal leakage repair generally are: grinding and cleaning of defective points, welding repair, elimination of residual stress, post-welding heat treatment, and quality inspection of welding. Before welding, it is necessary to analyze the chemical composition, mechanical properties, and welding performance of the valve body material, and select appropriate repair welding materials. To repair the internal leakage of the valve, you first need to expose the defective points and use an angle grinder to grind and clean them thoroughly. Only after the defects are completely removed can the next step of repair welding be carried out to avoid the generation of new defects. In the welding repair process, it is necessary to select an appropriate preheating temperature, interpass temperature, welding methods, welding voltage and welding current. The surface contact thermometer monitors the temperature in real time to avoid a decrease in welding strength and low-temperature impact toughness. In this process, an air hammer should be used to hammer the welding bead except the bottom welding seam to eliminate residual stress and prevent welding cracks. Quality inspection of welding includes non-destructive testing, hardness testing, metallographic testing and residual stress testing. After passing the quality inspection, the welding seam will be polished to make it flush with the original valve body and ensure the surface roughness of the welding seam.
3. Preventive measures
(1) Manufacturing and transportation stage: In the design stage, a multi-valve seat sealing structure can be used to improve the sealing performance of the valve; appropriate materials, heat treatment methods, assembly and processing techniques should be selected to improve the quality of the valve body; the water used in the hydraulic test should be clean and free of impurities, drying and anti-corrosion treatment should be carried out on the valve after completion, and appropriate anti-rust agents should be used to avoid corrosion of the sealing surface; the valve should be protected during transportation and blind plates should be installed on both sides of the valve to prevent hard particles from entering the sealing surface.
(2) Construction and installation stage: During the construction entry stage, strict acceptance will be carried out in accordance with various parameters and technical requirements of the valve, focusing on the integrity of the spherical surface and seal, and inspection of easily damaged parts such as grease nozzles; in the construction process, seal both sides of the valve and the opening of the pipeline to ensure that the internal environment of the valve and pipeline is clean and prevent rainwater and dirt from entering; the ball valve should be in the fully open position when welding the valve to avoid the influence of welding spatter, and the welding slag should be removed after welding; minimize the frequency of opening and closing the valve as much as possible during the construction and installation phase to avoid damage to the valve’s sealing surface.
(3) Operation and maintenance stage: abide by the operating procedures, and it is strictly prohibited to use the extension rod to operate the valve. When the valve does not move or is difficult to operate, follow-up operations can only be carried out after the fault is eliminated; carry out regular maintenance in accordance with standards, and use an appropriate cleaning agent and grease for valves; when the valve performs opening and closing operations, first use the bypass valve to level the pressure. It is strictly forbidden to force the valve to open when the differential pressure on both sides of the valve is too great; avoid long-term use of ball valves to adjust flow and pressure, and do a good job of upstream maintenance of filter separators to reduce damage to sealing surfaces caused by big impurities in natural gas.
4. Conclusion
Common faults of ball valves and corresponding measures are talked about, and a standardized workflow for internal leakage treatment of ball valves is put forward based on the analysis of the principle of internal leakages of ball valves; the following conclusions came:
(1) Strengthen the full life cycle management of valves and implement strict quality control during valve manufacturing, transportation, construction, installation, operation and maintenance.
(2) There are four main reasons for internal leakages of ball valves: incorrect valve limit, impurities on the sealing surface, damage to the sealing surface, and failures of the valve body. They can be dealt with by adjusting the valve limit, injecting grease, polishing and repairing.
2.2.5 Repairing internal leakages of valves
The processes of valve internal leakage repair generally are: grinding and cleaning of defective points, welding repair, elimination of residual stress, post-welding heat treatment, and quality inspection of welding. Before welding, it is necessary to analyze the chemical composition, mechanical properties, and welding performance of the valve body material, and select appropriate repair welding materials. To repair the internal leakage of the valve, you first need to expose the defective points and use an angle grinder to grind and clean them thoroughly. Only after the defects are completely removed can the next step of repair welding be carried out to avoid the generation of new defects. In the welding repair process, it is necessary to select an appropriate preheating temperature, interpass temperature, welding methods, welding voltage and welding current. The surface contact thermometer monitors the temperature in real time to avoid a decrease in welding strength and low-temperature impact toughness. In this process, an air hammer should be used to hammer the welding bead except the bottom welding seam to eliminate residual stress and prevent welding cracks. Quality inspection of welding includes non-destructive testing, hardness testing, metallographic testing and residual stress testing. After passing the quality inspection, the welding seam will be polished to make it flush with the original valve body and ensure the surface roughness of the welding seam.
3. Preventive measures
(1) Manufacturing and transportation stage: In the design stage, a multi-valve seat sealing structure can be used to improve the sealing performance of the valve; appropriate materials, heat treatment methods, assembly and processing techniques should be selected to improve the quality of the valve body; the water used in the hydraulic test should be clean and free of impurities, drying and anti-corrosion treatment should be carried out on the valve after completion, and appropriate anti-rust agents should be used to avoid corrosion of the sealing surface; the valve should be protected during transportation and blind plates should be installed on both sides of the valve to prevent hard particles from entering the sealing surface.
(2) Construction and installation stage: During the construction entry stage, strict acceptance will be carried out in accordance with various parameters and technical requirements of the valve, focusing on the integrity of the spherical surface and seal, and inspection of easily damaged parts such as grease nozzles; in the construction process, seal both sides of the valve and the opening of the pipeline to ensure that the internal environment of the valve and pipeline is clean and prevent rainwater and dirt from entering; the ball valve should be in the fully open position when welding the valve to avoid the influence of welding spatter, and the welding slag should be removed after welding; minimize the frequency of opening and closing the valve as much as possible during the construction and installation phase to avoid damage to the valve’s sealing surface.
(3) Operation and maintenance stage: abide by the operating procedures, and it is strictly prohibited to use the extension rod to operate the valve. When the valve does not move or is difficult to operate, follow-up operations can only be carried out after the fault is eliminated; carry out regular maintenance in accordance with standards, and use an appropriate cleaning agent and grease for valves; when the valve performs opening and closing operations, first use the bypass valve to level the pressure. It is strictly forbidden to force the valve to open when the differential pressure on both sides of the valve is too great; avoid long-term use of ball valves to adjust flow and pressure, and do a good job of upstream maintenance of filter separators to reduce damage to sealing surfaces caused by big impurities in natural gas.
4. Conclusion
Common faults of ball valves and corresponding measures are talked about, and a standardized workflow for internal leakage treatment of ball valves is put forward based on the analysis of the principle of internal leakages of ball valves; the following conclusions came:
(1) Strengthen the full life cycle management of valves and implement strict quality control during valve manufacturing, transportation, construction, installation, operation and maintenance.
(2) There are four main reasons for internal leakages of ball valves: incorrect valve limit, impurities on the sealing surface, damage to the sealing surface, and failures of the valve body. They can be dealt with by adjusting the valve limit, injecting grease, polishing and repairing.
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