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Key words: pipeline; plugging; sealant With the development of China's industry, the application of pipeline is gradually increasing. It is precisely because of the increase in the number of such use, the risk of leakage is gradually increasing. The method of pressure plugging has entered our line of sight.
I. Research status and development trend of pressure plugging technology The research on pressure plugging technology began in the 1920s. The British Feynmanite Co., Ltd. first proposed the concept of pressure plugging. As an advanced equipment maintenance technology, it is considered to have a good development prospect, and then gradually developed and applied, which proves the superiority of the technology to deal with leakage. In the 1960s, it began to develop rapidly in developed countries such as Britain, France, and Germany. In the 1970s, it was greatly improved in theory and technology, especially in the study of blocking media, fixture design, and sealant. Significant improvements have been made, from the initial sealing of a small amount of non-high temperature and high pressure medium to now it is able to block more than 300 kinds of medium, the temperature is from -195 ° C to 900 ° C, the pressure is vacuum ~ 60 MPa. The plugging fixtures are versatile, and the various sealants have been developed to withstand more and more leaking media and harsh conditions.
Second, the basic principle of pressure plugging technology with pressure plugging technology is a composite application technology, but also a special technology in the field of sealing technology, it involves many disciplines of the basic knowledge. Although this technology started late in China, it has developed rapidly. It has established sealing construction methods such as injection sealing method and fastening method, which are suitable for different working conditions. It has also successfully developed pressure-filled bonding method and drainage bonding method. The technology has been further strengthened by plugging technology such as magnetic compression bonding method. Its basic principle is: based on the mechanism of the sealant material itself, install a special fixture at the leaking part, contain the leak point with the clamp, establish a sealed cavity (or use the original sealed cavity), and inject the thrust higher than the pressure of the leaking system. The sealant reaches the working seal specific pressure and prevents the leakage of the medium, thereby achieving resealing. This technology consists of special sealants, special fixtures, special tools, and plugging technology.
Third, with pressure plugging technology features 1. Pressure plugging operation can be carried out in the normal operation of the production equipment, the process parameters can be kept unchanged during the operation, no need to take measures such as cooling, pressure reduction, returning materials, etc. Affect normal production.
2. The traditional welding sealing operation is easy to cause a safety accident, and when the pressure is plugged and sealed, no hot work is required, no spark is generated, and the safety is high.
3. When the pressure plugging operation is carried out, no special treatment is required on the surface and the similar parts of the leaking part, and the operation is simple, flexible, safe and fast.
4. During the plugging construction, the original sealing structure is not damaged, and the special sealing agent injected is determined by its own physical properties, does not adhere to the metal surface, has the characteristics of easy disassembly, and can conveniently locate the original leaking part. Perform a restorative overhaul.
5. In the case of blocking operation, 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 sealing technology, the wide adaptability of the technology will be more obvious.
6. Complete the sealing of the leakage point under the condition of non-stop production, and maintain the continuous normal operation of the production equipment, which can avoid the material loss and economic loss during the production stoppage of the production equipment, and maintain the material balance.
Fourth, the main method of pipe pressure plugging 1. Jig injection tape pressure seal domestic application range is more extensive, suitable for equipment pipeline flanges, pipe fittings (elbows, tees, straight through, etc.), valve stuffing letters. The principle is to establish a sealing structure under the dynamic operation of the medium, and the realization is realized by a clamp and a sealant. The fixture is an important tool for pressure plugging technology and must meet the requirements: First, sufficient mechanical strength and rigidity. Second, there must be a certain space with the leak point to facilitate the formation of a new sealing structure after the sealant is injected. The third is to have a proper number of well-structured injection holes. Fourth, it is necessary to have a proper gap with the original leak point to prevent running glue. The clamp injection pressure sealing method is the most widely used, and the applicable mediums include raw material gas, purified gas, steam, factory wind, sour gas, industrial water, rich and poor solution. It is also the direction of the development of pressure plugging technology in the future. There are many enterprises and research institutions to conduct research and promotion, which will not be repeated here.
2. The steel strip containment method uses the steel strip containment method for dynamic sealing operation. It has high requirements on the coaxiality of the two flanges, and the uniformity of the flange clearance is not high. Determine the number of installed injection fittings based on the flange size. When installing the steel strip, the steel strip should be placed on the gap between the two flanges, the connecting bolts should be slightly tightened, and then the two transitions, continue to tighten the bolts, and finally form a complete sealed cavity, and then dynamic sealing operation.
3. The plugging method is directly fixed in the leaking hole by a simple method of squeezing and clogging, thereby achieving a method of stopping leakage. This method is actually a simple mechanical plugging method, which is especially suitable for plugging defects such as blisters and small holes. One is the quilting method, which uses a punch to squeeze the metal body around the leak point to block the leak, called the quilting 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 method is the wedge method. The method of using a tough wedge or a wedge made of a tough metal, wood, plastic or the like to knock into a leaking hole is called a wedge method. This method is suitable for plugging leaks at low pressure points. The third method is the screw plug method, which drills and taps the hole in the leaked hole, and then tightens the screw plug and the gasket to treat the leak, which is called the screw plug method. This method is suitable for plugging leaks in areas where the volume is large and the holes are large.
4. Welding repair and sealing method The welding repair method is a method of blocking the leak directly or indirectly. This method is suitable for pipes with good welding performance and high medium temperature. It is not suitable for use in flammable and explosive situations. One is the direct welding method, which uses a welding rod to directly fill the leak at the leak and is called a straight welding method. This method is mainly suitable for plugging leaks in low pressure pipelines. The second is the interwelding method. The weld is not directly involved in plugging, but only acts as a method of fixing the gland and the seal, called the interwelding method. The inter-welding method is suitable for plugging in areas with large pressure, wide leakage surface, strong corrosiveness, small wall rigidity and small rigidity. The third is the welding method, which welds the leak in the metal cavity to achieve a leak detection method, called the welding method. This method is mainly suitable for flanges, threads, and plugging of valves and piping. The fourth is the method of welding the cover, which is covered with a metal cover on the leaking part, and is fixed by welding to prevent leakage. Suitable for plugging parts with large defects. If necessary, a drainage device can be placed on the cover. The fifth is the reverse welding method, which uses the principle of weld shrinkage to weld the leaked cracks one by one in the reverse direction, so that the crack shrinks and leaks, which is beneficial to the formation of the weld bead. The reverse welding method is also called the segmented reverse welding method. . This method is suitable for plugging leaks in low and medium pressure pipelines.
V. Precautions for pressure plugging and leakage 1. Supervision and management of the plugging site. The supervision and management of the plugging site should have a unified command structure to facilitate the analysis of the cause of the leak and the characteristics of the leaked site. The regulatory measures with clear division of labor and mutual coordination shall be adopted, strictly in accordance with the operating procedures and the established schemes. It is strictly forbidden to carry out pressure plugging for development defects with welds or base metals containing cracks and corrosion.
2. If the cause of the leak is unknown or cannot be accurately determined, it is not easy to make a fixture or the working surface is narrow, and the obstacles can not be filled with pressure. When the accident occurs, the leaking point that is not easy to evacuate cannot be blocked by pressure. Pressure plugging is only an emergency measure.
3. Selection of plugging agent. Because the plugging agent needs to have sufficient chemical stability, it is insoluble in the blocked medium. Before the injection of the fixture, the fluid leakage of the plugging agent is good and can fill all the 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 leaking point by the powerful injection pressure.
4. The temperature resistance after sealing is better, it does not decompose at the working temperature, has less volatilization, has certain strength and elasticity, and can ensure good sealing performance.
Conclusion: Pressure sealing is a kind of emergency repair work, which is characterized by safety, economy, adaptability, fast and efficient. The leak point with pressure plugging is a temporary treatment and has certain limitations. And timeliness. In the case of conditions, it is necessary to thoroughly overhaul the leaked parts, eliminate the phenomenon of “running, drowning, dripping and leaking†on the site, and improve the health of the equipment. It is necessary to rely on the rationality of the planned maintenance and improve the equipment maintenance. Maintenance process.
Analysis on Pressure Sealing Technology of Pipeline Valves in Thermal Power Plants
Abstract: The leaking part of the pipeline is often at the elbow. The reason is that the high-speed flowing medium in the pipeline washes the pipe wall for a long time, so that the pipe wall becomes thin and leaks. There are casting or forging defects in the pipeline and valve body during the production process, such as sand holes. , pores, cracks, etc. The pressure plugging is based on the sealing mechanism of the fluid medium under dynamic sealing material. The special equipment is installed in the leakage part, and the sealed cavity formed by the external part and the clamp of the leakage part is injected and filled with the sealed cavity. The pressure of the sealant is balanced with the pressure of the leaking medium, and a sealing structure is reconstructed to block the leaking pores and passages, blocking the leakage of the medium, thereby blocking the leak.