Abstract: Due to the influence of water, the welding method and welding equipment of underwater welding are much more complicated than those on land. This paper reviews the latest developments in the research and application of various underwater welding technologies, and introduces some new technologies in welding. The application status of the field and some views on the development trend of underwater welding technology.
Key words: underwater welding, wet underwater welding, local dry method, underwater welding, dry underwater welding, welding
Foreword
Because the offshore engineering structure works at sea all the year round, its working environment is extremely harsh. In addition to the structural working load, it is also subject to the additional loads caused by storms, waves, and currents, as well as seawater corrosion, sand erosion, earthquakes or ice in cold regions. Invasion. In addition, the flammability and explosive nature of oil and gas poses a threat to the structure. Moreover, the main part of the marine structure is under water. It is difficult and costly to inspect and repair the welded joints after service. In the event of major structural damage or overturning accidents, serious damage to life and property will result. Therefore, there are strict quality requirements for the design and manufacture of marine engineering structures, material selection and welding construction. With the development of the offshore oil and gas industry, marine pipeline engineering is advancing to the deep sea. As a developing coastal country, China's national economy must continue to develop, and the development and protection of the ocean must be a long-term strategic task. A large number of submarine pipeline construction projects have put forward new requirements for underwater welding technology.
Underwater welding makes the welding process more complicated due to the presence of water, and there are various problems that have not been encountered in land welding. At present, there are many types of underwater welding methods being applied and studied in various countries around the world. Mature is arc welding. With the development of underwater welding technology, in addition to the commonly used wet underwater welding, partial dry underwater welding and dry underwater welding, some new underwater welding methods have appeared. However, from the perspective of marine development in various countries, the research on underwater welding is far from being able to adapt to the needs of the development of the situation. Therefore, strengthening research in this area will be a very meaningful work, both now and in the future.
1 Latest developments in underwater welding technology
1.1 Wet underwater welding
In wet welding, the basic problems of underwater welding are most prominent. Therefore, it is difficult to obtain a good quality welded joint by such a method, especially in important applications, the quality of wet welding is unsatisfactory. However, wet underwater welding has the advantages of simple equipment, low cost, flexible operation and strong adaptability. Therefore, in recent years, countries continue to conduct research on this method, especially coated electrodes and manual arc welding, which will be further applied in the future.
In terms of welding rods, the more advanced Hydroweld FS underwater welding rod developed by British Hydroweld Company, the US patented underwater welding rod 7018'S welding rod, and the double developed by the Hanover University in Germany based on the influence of slag gas combined protection on droplet transfer and protection mechanism Layer self-protecting flux cored electrode. In the United States, Stephen Liu and others added manganese, titanium, boron and rare earth elements to the electrode coating to improve the welding performance during the welding process and refine the microstructure of the weld.
The development of underwater welding rods has promoted the application of wet underwater welding technology. At present, there are examples of underwater welding construction using underwater wet welding arc welding technology in the country, both inside and outside.
The emergence and development of flux-cored welding wire has adapted to the trend of high-efficiency, low-cost, high-quality, automated and intelligent welding production. The British TWI and the Ukrainian Barton Institute have successfully developed a wire-feeding structure, control system and welding process for underwater wet-process flux cored wire welding. Liu Sang and Zhong Jiguang from the Department of Mechanical and Electrical Engineering of South China University of Technology have developed a micro-drainage underwater welding method for flux-cored wire [3]. From the perspective of practical economy, it relies entirely on the gas generated by welding and the vaporization of water. The water vapor discharges water to form a stable, localized water-free zone where the arc can be stably burned. The size and structure of the micro-drainage cover determines the size and stability of the water-free zone (partial drainage zone) during the welding process. In addition, they also collected the arc welding underwater arc image of the flux-cored wire through the composite filter technology and the underwater CCD camera system, which laid the mechanism analysis and underwater welding process control for the underwater wet welding arc. The foundation.
Because the traditional edge detection operators such as gradient operator, Laplacian operator and Sobel operator are sensitive to noise, Liang Ming et al. used the Bubble function zero-crossing detection to extract the wavelet multi-scale method at the edge of the weld image. Adjusting the value of the scale parameter σ, the best σ range for the weld edge extraction is: 0.4 ≤ σ ≤ 0.6, which effectively reduces the noise, while maintaining the weld edge detail better, and welding the weld under the water core. Good results are obtained in edge detection.
Although wet welding has made great progress as mentioned above, it should be said that it is still difficult to obtain a good welded joint for wet underwater welding with a water depth of more than 100m, so it cannot be used for welding important marine engineering. structure. However, with the development of wet underwater welding technology, many problems of wet underwater welding are being overcome to some extent, such as the use of well-designed electrode coatings and waterproof coatings, plus strict welding process management and certification. Nowadays, wet underwater welding has been successfully applied in underwater repair of auxiliary components of the North Sea platform. In addition, wet underwater welding technology is also widely used in shallow water areas with good marine conditions and welding without requiring high stress components. . At present, the most widely used wet underwater electrode and wet underwater welding technology in the world is the Gulf of Mexico. The most common methods used in wet underwater welding are electrode arc welding and flux cored arc welding. When welding, the submersible welder uses electrodes with waterproof coatings and welding tongs specially designed or modified for underwater welding. In the case of high quality requirements, the electrode can be placed in an inflatable container to prevent the electrode from absorbing water before use.
1.2 Local dry underwater welding
There are many types of local dry underwater welding, including dry box welding, dry point welding, water curtain dry welding, steel brush underwater welding, and local dry large hood underwater MIG/TIG welding. Since local dry underwater welding reduces the harmful effects of water, the quality of welded joints is significantly improved over wet welding.
The Harbin Welding Research Institute of China conducted earlier research on semi-automatic underwater welding of CO2 gas protection partial drainage, developed the LD-CO2 welding method, and developed the NBS-500 underwater semi-automatic welding machine, which was carried out many times in China. Successful welding. The Underwater Welding Research Group of South China University of Technology has successfully developed a set of underwater partial dry flux cored wire welding equipment and technology using micro drain cover, which lays a foundation for further development into an underwater welding method suitable for China's national conditions.
Next page
Galvanized Square Tube,Rectangular Hollow Tube,Square Hollow Steel Tube
Steel Tubing,Stainless Pipe Co., Ltd. , http://www.czsteelpipes.com