Self-sealing Leakage of High-pressure Valves
In the production process of offshore and onshore natural gas treatment facilities, the valves used are basically high-temperature and high-pressure valves and their main functions are to control the flow of natural gas, boilers and related equipment. In this process, the high-pressure valve is prone to leak, and long-term leakage will damage the valve and increase the risk of on-site mining and treatment. Therefore, in the process of natural gas operation, it is necessary to use effective means to study the leakage problem of high-pressure valves, pay close attention to its operation process, fully control the fault problem of high-pressure valves, and work out solutions as soon as possible so that the high-pressure valves can operate normally and efficiently.
Self-sealing Leakage of High-pressure Valves
The valve leakage is mainly divided into two types, one is internal leakage and the other is external leakage. It is difficult to find the internal leakage of the valve, and it is relatively difficult to detect it. From the current development point of view, there are three main detection methods of leakage in high-pressure valves, namely pressure method, temperature detection method and acoustic method. First of all, the pressure method is based on the principle of setting pressure sensors along the pipeline and at the position of valves. The collected pressure signals are summarized together, and then the pressure distribution diagram of the system is set up. According to the data provided by the pressure curve, the location and degree of leakage are determined. There are some limitations in the way of temperature detection, which can be used to effectively calculate the leakage flow in places where the temperature of the detected fluid is obviously higher than the normal ambient temperature. Inside the pipelines produced by power plants, most of them are steam with high pressure and high temperature, and the temperature difference is very large. Using the temperature detection method to detect, the effect is better. Acoustic detection is quite special. If the self-sealing leakage of the high-pressure valve occurs, the leaked fluid will generate jet noise and spread through the valve wall. At this time, the sensor can effectively accept this stress wave and sort out the leakage degree of the high-pressure valve through analysis and treatment.
Common Forms of High-pressure Valves Self-sealing Leakage
1. Leakage of valve packing
During the operation of the high-pressure valve, the valve stem and packing move relatively, including axial movement and rotation. If the number of switches increases, the number of relative movements will also increase, and the valve packing is prone to leak due to the influence of temperature.
2. Flange leakage of high-pressure valves
In the high-pressure valve, the sealing of the flange mainly depends on the pre-tightening force of the connecting shaft bolt, which will increase the sealing specific pressure through the gasket, thus preventing the leakage of the sealed pressure fluid medium. There are many factors that affect the leakage, such as insufficient pressure of sealing gasket, the roughness of joint surface that can not meet the use requirements, and deformation of the gasket, etc., all of which will lead to the leakage problem.
3. There is a leakage problem in the valve body.
If there are problems in the production or casting process of the high-pressure valve, which leads to certain defects, such as cracks, air holes or sand holes, the valve body is very easy to leak. At the same time, the erosion of fluid medium and gas erosion in the process of natural gas production are also common forms of valve body leakage.
Main Causes of High-pressure Valves Self-sealing Leakage
1. The medium pressure and temperature change greatly.
In the process of natural gas production, the problems of unstable engineering conditions and large fluctuations in temperature and pressure often occur. These problems will cause a serious impact on the sealing ring, scouring and squeezing the sealing ring. If these production conditions occur frequently, the gap between the valve body and the sealing ring will become larger and larger, and eventually, the leakage problem will occur.
2. The valve maintenance is not sophisticated enough.
In the process of valve disassembly and maintenance, if the cover of the sealing ring is not cleaned up, there are small particles of impurities, or there are certain longitudinal scratches in the process of maintenance, and then after continuous running-in, serious scratches will be formed in the long run.
3. The sealing ring is corroded.
During the design process of the sealing ring, we must ensure that its strength and corrosion resistance meet the production needs. If the design is unreasonable, the surface hardness of the sealing ring is lower than that of the bonnet seal layer, and plastic deformation will occur under the constant action of external forces. If the water quality is not properly treated, the sealing ring will corrode during long-term operation, which will eventually lead to leakage.
Practical Treatment Measures of High-pressure Valve Self-sealing Leakage
1. Use mechanical tools to complete plugging.
Using mechanical tools for plugging is the prerequisite for plugging under pressure. In the actual operation process, the mechanical support frame is set outside the pipeline of the high-pressure valve, and then corresponding tools and equipment or gaskets are used to plug the leaked part. This way is very suitable for very large pipelines in the process of plugging. In the process of mechanical operation, relevant technicians need to jam the gasket at the leaking position, so as to achieve a better leakage filling effect and ensure the normal operation of the high-pressure valve. Mechanical leak filling is also very effective in the low-pressure state of offshore or onshore natural gas production and processing facilities, or in pipelines that are beneficial to operation, and can be effectively applied, so its application range is very wide.
2. Use a plug hole to start plugging work.
In general, plugging with plug holes is very simple and easy to operate. After the object is extruded, it is fixed in the leaking hole, which effectively solves the leakage problem of high-pressure valves in offshore or onshore natural gas production and treatment facilities. However, it should be noted that plugging by plug hole is basically only suitable for self-sealing defects of high-pressure valves such as small holes or sand holes. If it is a non-hard material such as cast iron welding or alloy steel welding seam, or a leak with severe corrosion, the plug hole is not suitable for plugging.
3. Perforation and injection of sealant for plugging
In the process of self-sealing leakage treatment of a high-pressure valve, the sealing agent can be injected by drilling holes for effective sealing. During the implementation process, you can observe the specific location of the leakage point, and then measure the implementation height of the seal at the location where the leakage occurs, and punch holes outside the sealing ring and the valve body, and the depth setting needs to be equal to the thickness of the valve body wall at this location. After the sealant is injected, injection plugging is required. This method is only effective for soft sealing rings. If it is a hard metal sealing ring with a very small gap, there is no way to effectively inject sealant. Therefore, when the method of punching and injecting sealant is applied, it needs to be used according to the specific situation.
4. Leak stoppage by means of welding repair
The method of welding and plugging is well applied in high-pressure valves with very good weldability or pipelines with relatively high medium temperature and is not suitable for locations where pipelines are flammable and explosive. In the process of plugging by welding repair, welding repair plugging plays the role of fixing gland or seal and is more suitable for plugging valves of offshore or onshore natural gas production and processing facilities with very high pressure, wide leakage area, strong corrosiveness and relatively small wall rigidity, which can promote the safety of offshore or onshore natural gas production and processing facilities of high-pressure valves.
5. Improve the assembly accuracy of the high-pressure valve during maintenance.
The structure of the high-pressure self-sealing valve is very complicated, and the arrangement between the components is very compact and the size is relatively symmetrical. Technicians need to be more patient when unfolding and disassembling and pay attention to the assembly accuracy during installation. Only by paying attention to the safety inspection of the valve, the pressure test rate after valve repair will be higher, and the service process will be more lasting. Relevant technicians need to continuously improve the valve technology from the aspects of the smoothness of the valve surface, the position tolerance between shapes, and the sealing fit. If the sealing surface is seriously damaged, turning is needed at this time, and high-strength cemented carbide needs to be hard-faced and heat-treated repeatedly. If the technology is too complicated and the repair is very difficult, it is necessary to transport the valve to the manufacturer in time for stricter maintenance.
Conclusion
All in all, the self-sealing leakage of high-pressure valves brings serious potential safety hazards to natural gas treatment facilities, and its harmfulness and destructive power are very great. Therefore, in the normal operation of offshore or onshore natural gas production and treatment facilities, if there is a problem of self-sealing leakage of high-pressure valves, relevant technicians must analyze the root cause of the problem in time, and work out solutions to solve the problem, so as to reduce the leakage of high-pressure valves and improve production efficiency.
Self-sealing Leakage of High-pressure Valves
The valve leakage is mainly divided into two types, one is internal leakage and the other is external leakage. It is difficult to find the internal leakage of the valve, and it is relatively difficult to detect it. From the current development point of view, there are three main detection methods of leakage in high-pressure valves, namely pressure method, temperature detection method and acoustic method. First of all, the pressure method is based on the principle of setting pressure sensors along the pipeline and at the position of valves. The collected pressure signals are summarized together, and then the pressure distribution diagram of the system is set up. According to the data provided by the pressure curve, the location and degree of leakage are determined. There are some limitations in the way of temperature detection, which can be used to effectively calculate the leakage flow in places where the temperature of the detected fluid is obviously higher than the normal ambient temperature. Inside the pipelines produced by power plants, most of them are steam with high pressure and high temperature, and the temperature difference is very large. Using the temperature detection method to detect, the effect is better. Acoustic detection is quite special. If the self-sealing leakage of the high-pressure valve occurs, the leaked fluid will generate jet noise and spread through the valve wall. At this time, the sensor can effectively accept this stress wave and sort out the leakage degree of the high-pressure valve through analysis and treatment.
Common Forms of High-pressure Valves Self-sealing Leakage
1. Leakage of valve packing
During the operation of the high-pressure valve, the valve stem and packing move relatively, including axial movement and rotation. If the number of switches increases, the number of relative movements will also increase, and the valve packing is prone to leak due to the influence of temperature.
2. Flange leakage of high-pressure valves
In the high-pressure valve, the sealing of the flange mainly depends on the pre-tightening force of the connecting shaft bolt, which will increase the sealing specific pressure through the gasket, thus preventing the leakage of the sealed pressure fluid medium. There are many factors that affect the leakage, such as insufficient pressure of sealing gasket, the roughness of joint surface that can not meet the use requirements, and deformation of the gasket, etc., all of which will lead to the leakage problem.
3. There is a leakage problem in the valve body.
If there are problems in the production or casting process of the high-pressure valve, which leads to certain defects, such as cracks, air holes or sand holes, the valve body is very easy to leak. At the same time, the erosion of fluid medium and gas erosion in the process of natural gas production are also common forms of valve body leakage.
Main Causes of High-pressure Valves Self-sealing Leakage
1. The medium pressure and temperature change greatly.
In the process of natural gas production, the problems of unstable engineering conditions and large fluctuations in temperature and pressure often occur. These problems will cause a serious impact on the sealing ring, scouring and squeezing the sealing ring. If these production conditions occur frequently, the gap between the valve body and the sealing ring will become larger and larger, and eventually, the leakage problem will occur.
2. The valve maintenance is not sophisticated enough.
In the process of valve disassembly and maintenance, if the cover of the sealing ring is not cleaned up, there are small particles of impurities, or there are certain longitudinal scratches in the process of maintenance, and then after continuous running-in, serious scratches will be formed in the long run.
3. The sealing ring is corroded.
During the design process of the sealing ring, we must ensure that its strength and corrosion resistance meet the production needs. If the design is unreasonable, the surface hardness of the sealing ring is lower than that of the bonnet seal layer, and plastic deformation will occur under the constant action of external forces. If the water quality is not properly treated, the sealing ring will corrode during long-term operation, which will eventually lead to leakage.
Practical Treatment Measures of High-pressure Valve Self-sealing Leakage
1. Use mechanical tools to complete plugging.
Using mechanical tools for plugging is the prerequisite for plugging under pressure. In the actual operation process, the mechanical support frame is set outside the pipeline of the high-pressure valve, and then corresponding tools and equipment or gaskets are used to plug the leaked part. This way is very suitable for very large pipelines in the process of plugging. In the process of mechanical operation, relevant technicians need to jam the gasket at the leaking position, so as to achieve a better leakage filling effect and ensure the normal operation of the high-pressure valve. Mechanical leak filling is also very effective in the low-pressure state of offshore or onshore natural gas production and processing facilities, or in pipelines that are beneficial to operation, and can be effectively applied, so its application range is very wide.
2. Use a plug hole to start plugging work.
In general, plugging with plug holes is very simple and easy to operate. After the object is extruded, it is fixed in the leaking hole, which effectively solves the leakage problem of high-pressure valves in offshore or onshore natural gas production and treatment facilities. However, it should be noted that plugging by plug hole is basically only suitable for self-sealing defects of high-pressure valves such as small holes or sand holes. If it is a non-hard material such as cast iron welding or alloy steel welding seam, or a leak with severe corrosion, the plug hole is not suitable for plugging.
3. Perforation and injection of sealant for plugging
In the process of self-sealing leakage treatment of a high-pressure valve, the sealing agent can be injected by drilling holes for effective sealing. During the implementation process, you can observe the specific location of the leakage point, and then measure the implementation height of the seal at the location where the leakage occurs, and punch holes outside the sealing ring and the valve body, and the depth setting needs to be equal to the thickness of the valve body wall at this location. After the sealant is injected, injection plugging is required. This method is only effective for soft sealing rings. If it is a hard metal sealing ring with a very small gap, there is no way to effectively inject sealant. Therefore, when the method of punching and injecting sealant is applied, it needs to be used according to the specific situation.
4. Leak stoppage by means of welding repair
The method of welding and plugging is well applied in high-pressure valves with very good weldability or pipelines with relatively high medium temperature and is not suitable for locations where pipelines are flammable and explosive. In the process of plugging by welding repair, welding repair plugging plays the role of fixing gland or seal and is more suitable for plugging valves of offshore or onshore natural gas production and processing facilities with very high pressure, wide leakage area, strong corrosiveness and relatively small wall rigidity, which can promote the safety of offshore or onshore natural gas production and processing facilities of high-pressure valves.
5. Improve the assembly accuracy of the high-pressure valve during maintenance.
The structure of the high-pressure self-sealing valve is very complicated, and the arrangement between the components is very compact and the size is relatively symmetrical. Technicians need to be more patient when unfolding and disassembling and pay attention to the assembly accuracy during installation. Only by paying attention to the safety inspection of the valve, the pressure test rate after valve repair will be higher, and the service process will be more lasting. Relevant technicians need to continuously improve the valve technology from the aspects of the smoothness of the valve surface, the position tolerance between shapes, and the sealing fit. If the sealing surface is seriously damaged, turning is needed at this time, and high-strength cemented carbide needs to be hard-faced and heat-treated repeatedly. If the technology is too complicated and the repair is very difficult, it is necessary to transport the valve to the manufacturer in time for stricter maintenance.
Conclusion
All in all, the self-sealing leakage of high-pressure valves brings serious potential safety hazards to natural gas treatment facilities, and its harmfulness and destructive power are very great. Therefore, in the normal operation of offshore or onshore natural gas production and treatment facilities, if there is a problem of self-sealing leakage of high-pressure valves, relevant technicians must analyze the root cause of the problem in time, and work out solutions to solve the problem, so as to reduce the leakage of high-pressure valves and improve production efficiency.
