Progress in research and application of the hottes

Progress in the research and application of underwater welding technology

Abstract: due to the influence of water, the welding methods and welding equipment of underwater welding are much more complex than those on land. This paper summarizes the latest progress in the research and application of various underwater welding technologies, introduces the application status of some new technologies in the field of welding, and puts forward some views on the development trend of underwater welding technology

key words: underwater welding wet underwater welding partial dry underwater welding dry underwater welding welding welding method

preface

due to working at sea all year round, the working environment of offshore engineering structures is extremely harsh. In addition to the working load of the structure, they also bear the additional load caused by storms, waves, tidal currents, seawater corrosion, sand flow abrasion, earthquake or ice flow invasion in cold areas. In addition, the flammability and explosion of oil and natural gas also pose a threat to the structure. Moreover, the main part of the offshore structure is underwater, and the inspection and repair of the welded joints after service are very difficult and expensive. Once a major structural damage or overturning accident occurs, it will cause serious losses of life and property. Therefore, there are strict quality requirements for the design and manufacture, material selection and welding construction of offshore engineering structures. With the development of offshore oil and natural gas industry, offshore pipeline engineering is increasingly advancing to the deep sea. As a developing coastal country, China must take the development and protection of the ocean as a long-term strategic task in order to achieve sustainable national economic development. A large number of submarine pipeline construction projects put forward new requirements for underwater welding technology

underwater welding due to the existence of water, the welding process becomes more complex, and there will be a variety of problems that have not been encountered in land welding. At present, there are a wide range of underwater welding methods being applied and studied all over the world, and the more mature application is arc welding. With the development of underwater welding technology, in addition to the commonly used wet underwater welding, local dry underwater welding and dry underwater welding, some new underwater welding methods have emerged. However, from the perspective of ocean development in various countries, the research of underwater welding is far from meeting the needs of the development of the situation. Therefore, it will be a very meaningful work to strengthen the research in this area, both now and in the future

1 the latest development of underwater welding technology

1.1 wet underwater welding

in wet welding, the basic problems of underwater welding are the most prominent. Therefore, it is difficult to obtain high-quality welded joints by this method, especially in important applications, the quality of wet welding is difficult to be satisfactory. However, wet underwater welding has the advantages of simple equipment, low cost, flexible operation and strong adaptability. Therefore, in recent years, countries continue to study 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 ones are the hydroweld FS underwater welding rod developed by the British hydroweld company, the American patented underwater welding rod 7018's welding rod, and the double-layer self protective flux cored electrode developed by Hanover University in Germany based on the influence of slag gas joint protection on droplet transfer and protection mechanism. Stephen Liu of the United States and others added manganese, titanium, boron and rare earth elements to the electrode coating, which improved the welding performance during the welding process and refined the microstructure of the weld [1]

because traditional edge detection operators such as gradient operator, Laplace operator and Sobel operator are sensitive to noise, Liang Ming et al. Used the wavelet multi-scale method of bubble function zero crossing detection to extract the edge of weld image [4] by adjusting the scale parameters σ Get the best result of weld edge extraction σ The range is: 0.4 ≤ σ ≤ 0.6, which effectively reduces the noise, while better maintaining the details of the weld edge, and achieves good results in the underwater flux cored welding weld edge detection

although wet welding has made great progress as mentioned above, so far, it should be said that it is still difficult to get a good welding joint for wet underwater welding with a water depth of more than 100m. Therefore, the center of the platform is gradually adjusted and aligned, which cannot be used for welding important offshore engineering structures. However, with the development of wet underwater welding technology, many problems of wet underwater welding are being overcome to a certain extent, such as the use of well-designed electrode coating and waterproof coating, coupled with strict welding process management and certification, now wet underwater welding has been successfully applied in the underwater repair of auxiliary components of Beihai platform. In addition, Wet underwater welding technology is also widely used in shallow water areas with good marine conditions and the welding of components that are not required to bear high stress. At present, the Gulf of Mexico is the most widely used wet underwater electrode and wet underwater welding technology in the world. At present, the most commonly used methods in wet underwater welding are electrode arc welding and flux cored wire arc welding. When welding, submerged welders should use electrodes with waterproof paint and welding tongs specially designed or modified for underwater welding. In the occasions with high quality requirements, the welding rod can be put into the inflatable container to prevent the welding rod from absorbing water before use

1.2 local dry underwater welding

there are many kinds of local dry underwater welding, including dry box welding, dry spot welding, water curtain dry welding, steel brush underwater welding and local dry large hood underwater mig/tig welding. Because local dry underwater welding reduces the harmful effects of water, the quality of welded joints has been significantly improved compared with wet welding

Harbin Welding Research Institute of China has studied the CO2 gas shielded partial drainage semi-automatic underwater welding earlier, developed the ld-co2 welding method, and developed the supporting nbs-500 underwater semi-automatic welding machine, which has been successfully welded for many times in China. The underwater welding research group of South China University of technology has successfully developed a set of underwater local dry flux cored wire welding equipment and process using a micro drainage cover, which has laid a foundation for further developing an underwater welding method suitable for China's national conditions

the water curtain underwater welding method was first proposed by Japan. The welding gun structure of the usual water curtain welding is divided into two layers. The strength of the welded joint of this method is not lower than that of the base metal, and the face bending and back bending of the welded joint can reach 180 degrees. The welding gun is light and flexible, but the visibility problem has not been solved. The water in the welding area is muddy and disordered by shielding gas and smoke, and the welder is basically in a blind welding state. In addition, the distance and inclination between the nozzle and the surface of the weldment are strict, and the requirements for the operation technology of the welder are high. In addition, the reverse effect of the steel plate on the high-pressure water, this method is not effective in welding lap joints and angle joints, and manual welding is very difficult, so it should be developed in the direction of automation. Recently, Japan has successfully developed a mechanized water curtain underwater welding mechanism, which can weld large underwater moving components well [5]. For water curtain local dry underwater welding, Hoffmeister et al. Established the relationship between the minimum protective airflow and heat input and pressure when reducing hydrogen adsorption. Mattias et al. Designed a new exhaust hood based on their understanding of the principle of radial flow extractor, which reduced the air pressure in the welding area in the hood and obtained good welds

Zhang Xudong et al. Studied the underwater local dry laser welding, and studied the basic physical phenomena of underwater laser welding by using the method of wire filling thermal conductivity welding. The use of gas nozzles to form a local dry space, its protection effect depends on the nozzle structure and gas flow and other parameters, the nozzle outer diameter has a significant impact on the protection effect, and the mechanical properties of underwater welds under good protection conditions are consistent with those in the atmosphere [6]

compared with dry welding, local dry welding does not need large and expensive drainage chamber, and its adaptability is significantly increased. It combines the advantages of wet and dry methods. It is an advanced underwater welding method, and it is also the focus and direction of current underwater welding research. Local dry underwater welding can directly obtain the joint quality close to the next step. At the same time, it is a promising underwater welding method because of its simple equipment, low cost and flexibility of wet welding

1.3 dry underwater welding

dry welding is a method that uses gas to remove the water around the welding part, while the submerged welder is welding under completely dry or semi dry conditions. When carrying out dry underwater welding, it is necessary to design and manufacture complex pressure chambers or workrooms. According to the different pressures in the pressure chamber or working chamber, dry underwater welding can be divided into high-pressure dry underwater welding and atmospheric pressure dry underwater welding

1.3.1 high pressure dry underwater welding

dry underwater welding tests are generally carried out in the high-pressure simulation cabin, and welding procedure qualification tests can also be carried out in the pressure cabin. Harbin Welding Research Institute has been studying dry underwater welding since the 1980s. First, the experimental research is carried out in the simulation experiment cabin, and then the actual field verification is carried out. Chen Jinhong and Xiao Zhiping repaired a river crossing pipe in Guangzhou by high-pressure dry welding, which has made new development in underwater welding technology in China [7]. The underwater high-pressure welding cabin of cenpes center in Brazil consists of six parts: environmental control room, gas supply room, gas recovery room, high-pressure room, electrical control room and automatic welding machine. High voltage automatic TIG, MIG, FCAW and SMAW welding processes can be carried out. GKSS center in Germany has studied the short-circuit transition behavior of a special fresh-keeping film welding blown out by flux cored wire arc blow molding machine at a water depth of 600 ~ 1100 meters, the influence of power output and gradient on droplet transition, the reaction mechanism of molten pool, the influencing factors of oxygen adsorption and the selection of shielding gas. The research results have been applied to the design of high-pressure welding cabin and achieved satisfactory results. In the past seven years, the welding engineering research center of Cranfield University has applied the automatic welding technology to the deep-water welding under the condition of 2500m water depth and 250bar pressure [8, 9]. This deep-water high-pressure welding research is carried out in three stages:

stage 1: with the development, optimization and trial operation of welding auxiliary equipment, under the condition that the welding process is all linear welds, the pressure range is demonstrated to be in the range of 0 ~ 250bar, Welding of plasma arc welding and GMAW welding