Analysis of Pressure Leakage Stopping Technology for Pipe Valves in Thermal Power Plants
Release time：2019-12-25 Author：fzy667 Source：Xingda Valve
With the development of China's industry, the application of pipelines is gradually increasing. Because of this increase in the number of uses, the risk of leakage is gradually increasing. At this time, the method and technology of plugging with pressure will be gone. Into our sight.
I. Research Status and Development Trend of Leakage Plugging with Pressure
The research on pressure plugging technology began in the 1920s. The British Femmernet Ltd. first proposed the concept of pressure plugging technology. They regarded pressure plugging technology as an advanced equipment maintenance technology, Very good development prospects, followed by gradual R & D and application, confirmed the superiority of the technology to deal with leakage. Since the 1960s, it has developed rapidly in developed countries such as Britain, France, and Germany. In the 1970s, it has greatly improved in theory and technology, especially in the study of plugging media, fixture design, and sealants. Significant improvements have been made. From the beginning, only a small amount of non-high-temperature and high-pressure media can be blocked to more than 300 media, which has a temperature of -195 ° C to 900 ° C and a pressure of vacuum to 60MPa. The plugging fixtures are diverse, and the various sealants developed can withstand more and more leaking media and harsh conditions.
Second, the basic principle of pressure leak plugging technology
Leakage plugging technology with pressure is a composite application technology and a special technology in the field of sealing technology. It involves many disciplines and basic knowledge. Although this technology started late in China, it has developed rapidly. It has established seal construction methods that adapt to different working conditions, such as injection seal method and tightening seal method. It has also successfully developed the pressure-filled and bonded method and the drainage and bonded method. Leak plugging technologies such as magnetic compression and bonding method have further enhanced the technical efficiency. Its basic principle is: Based on the mechanism of the sealant material itself, install a special fixture at the leak site, use the fixture to contain the leak point, establish a sealed cavity (or use the original sealed cavity), and inject it with a thrust higher than the pressure of the leaking system The sealant achieves the specific pressure of the working seal and prevents the leakage of the medium, thereby achieving reseal. This technology consists of special sealant, special fixture, special tool, and plugging operation technology.
Third, the technical characteristics of plugging under pressure
1. The plugging operation under pressure can be carried out while the production equipment is kept in a normal operating state, and the process parameters can be maintained during the operation without the need to take measures such as temperature reduction, pressure reduction, and material return, which does not affect normal production.
2. Traditional welding and plugging operations are prone to cause safety accidents. When plugging under pressure and leaking, they do not require any hot work, do not generate sparks, and have high safety.
3. When the leak is plugged under pressure, no special treatment is required for the surface of leaking parts and nearby parts, and the operation is simple, flexible, safe and fast.
4. During the plugging construction, the original sealing structure is not damaged. The special sealant injected is determined by its own physical characteristics, does not adhere to the metal surface, has the characteristics of easy disassembly, and can easily be used for the original leakage site. Perform restorative maintenance.
5. In the process of plugging, in principle, it is not limited by the objective working conditions of the construction site, and the leakage of various media can be eliminated. With the improvement and improvement of the overall level of the plugging technology, the broad adaptability of the technology will be more obvious.
6. Complete the plugging of the leak point under non-stop production conditions, and maintain the continuous normal operation of the production equipment, which can avoid material loss and economic loss during production equipment shutdown and maintenance, and maintain material balance.
Fourth, the main method of pipeline plugging
1. Fixture with adhesive tape pressure seal
It has a wide range of domestic applications and is suitable for equipment pipeline flanges, pipe fittings (elbows, tees, straight through, etc.), stuffing boxes for valves, etc. The principle is to establish a sealing structure under the dynamic operation of the medium, and its realization is achieved by a clamp and a sealant. The fixture is an important tool for pressure plugging technology, which must meet the requirements: First, sufficient mechanical strength and stiffness. The second is to have a certain space with the leak point, so that a new seal structure can be formed after the sealant is injected. Third, there are injection holes with proper quantity and reasonable structure. The fourth is to have a proper gap with the original leak point to prevent running glue. The most popular application is the method of pressure-sealing with adhesive tape, and the applicable media are raw material gas, purified gas, steam, factory air, acid gas, industrial water, poor and rich solutions, etc. It is also the direction for the development of pressure plugging technology in the future. There are many companies and research institutions to conduct research and promotion.
2. Steel belt containment method
The steel band enclosure method is used for dynamic sealing operation. It has high requirements for the coaxiality of the two flanges, and not high requirements for the uniformity of the flange gap. Determine the number of mounting injection fittings according to the flange size. When installing the steel belt, the steel belt should be located on the gap between the two flanges, and the connection bolts should be twisted a few buckles, and then the two transitions will be continued, and the bolts will continue to be tightened to form a complete sealed cavity, and then the dynamic sealing operation is performed.
3. Plugging method
A simple method of squeezing and blocking is directly fixed in the leakage hole, thereby achieving a method of preventing leakage. This method is actually a simple mechanical plugging method, and it is especially suitable for plugging defects such as trachoma and small holes. The first is the caulking method, which uses a punch to squeeze the metal body around the leak point to block the leak, which is called the caulking method. This method is suitable for alloy steel, carbon steel and carbon steel welds. It is not suitable for hard and brittle materials such as cast iron and alloy steel welds, as well as bodies with severe corrosion and thin walls. The second is the plug wedge method. A cone wedge or flat wedge made of a tough metal, wood, plastic or other material is used to knock into the leaking hole to stop the leak. This method is suitable for plugging leaks where the pressure is not high. The third is the screw plug method. The method of drilling and tapping in the leaking hole, and then tightening the screw plug and the gasket to prevent leakage is called the screw plug method. This method is suitable for plugging in the thick and large holes.
4. Welding repair and plugging method
Welding method is a method to plug the leak directly or indirectly. This method is suitable for pipes with good welding performance and high medium temperature. It is not suitable for flammable and explosive occasions. The first is the direct welding method, which uses a welding rod to directly fill the leak to prevent leakage, which is called the direct welding method. This method is mainly applicable to plugging of low-pressure pipelines. The second is the method of indirect welding, in which the weld does not directly participate in plugging, but only plays a role of fixing the gland and seal, which is called indirect welding. The indirect welding method is suitable for plugging in places with large pressure, wide leakage area, strong corrosion, thin wall and small rigidity. The third is the welding package method, which is a method of welding the leak in the metal cavity to achieve leakage control, which is called the welding package method. This method is mainly applicable to the plugging of flanges, threads, and valves and pipelines. The fourth is the welding cover method, which covers the leakage site with a cover metal and uses a method of welding to fix the leakage. It is suitable for plugging parts with larger defects. If necessary, a drainage device can be provided on the cover. Fifth is the reverse welding method, which uses the principle of welding seam shrinkage to reversely leak leak cracks one by one to make up the cracks so that the cracks do not leak. The plugging method is conducive to the formation of weld beads. . This method is suitable for plugging of low and medium pressure pipelines.
V. Precautions for plugging under pressure
1. Supervision and management of plugging site. The supervision and management of the plugging site should have a unified command mechanism to facilitate on-site analysis of the cause of the leak and the characteristics of the leak site. Supervisory measures with clear division of labor and coordinated measures shall be adopted, and strictly in accordance with the operating regulations and established plans. It is strictly forbidden to plugging under pressure for developmental defects with cracks and severe corrosion in the weld or parent metal.
2. The cause of the leak is unknown or cannot be accurately determined. It is not easy to make fixtures or narrow working surfaces. Many obstacles cannot be plugged under pressure. Leakage points that are not easy to evacuate when an accident occurs cannot be plugged under pressure. Plugging under pressure is only an emergency measure.
3. Selection of plugging agent. Because the plugging agent needs to be selected with sufficient chemical stability, it is insoluble in the blocked medium. Before injection into the jig, the plugging agent should have good fluidity and be able to fill all cracks. At the same time, the curing time should not be too long, and the plugging agent will be squeezed into the pipeline from the leak point by the strong injection pressure.
4. The temperature resistance after sealing is better, it does not decompose and less volatilize at the working temperature, has certain strength and elasticity, and can ensure good sealing performance.
Leakage plugging under pressure is a kind of emergency repair work, which has the characteristics of safety, economy, adaptability, fast and high efficiency. The leaking point under pressure leak plugging treatment is a temporary treatment measure, which has certain limitations and timeliness. . Under conditions, thorough inspection and repair of the leaked parts are needed to eliminate the “running, dripping, dripping, and leaking” phenomenon on the site, and the fundamental way to improve the health level of equipment operation is to rely on the rationality of planned maintenance and improve equipment maintenance Maintenance process.