Summary of wet underwater welding

Underwater welding is refers to the underwater, welding of the metal structure of a professional technology. Underwater welding has both the influence of the presence of water and the effect of high pressure, so the underwater welding technology, equipment and its requirements on quality and there is a difference between land. At present, a lot of methods of underwater welding, generally can be divided into wet underwater welding, dry underwater welding and local underwater welding. 
Wet underwater welding, the divers do not take any drainage measures and direct welding method. Using this method, the main problems is that the poor visibility, not easy to control, fast cooling speed, high hydrogen content affect the quality of welding joint. 
In 1954 first put forward by the United States the concept of dry underwater welding, namely, including welding parts, a broader range of water, the welding process is in the environment of a dry gas box. Main problems of this method: first of all, to have a big room, but is limited by underwater shape dimension and position of welding, adaptability is poor, so far, this method is only undersea pipeline welding shapes such as simple structure; Second must have a maintenance, adjustment, monitoring, lighting and security control of the complete equipment system, the cost of expensive; Still exists the third pressure influence on welding quality, with the increase of the depth of the water, the welding arc is compressed, arc column and weld bead and weld width narrowing, bad and easy to cause defects of weld formation. 
Local dry welding, underwater wet underwater welding, simple equipment, easy operation, low cost, but the welding quality is poor. And dry underwater welding, although the welding quality is higher, but this is expensive, poor adaptability and is difficult to meet the development of ocean development business, and so people developed a kind of local dry underwater welding. This welding method is local waters around the welding parts of water, artificial emptying, form a local gas tank area, in which the arc stability of combustion. Compared with wet method, due to welding parts to exclude the interference of water, thus improving the joint quality. Compared with the dry method, and don't need that huge equipment system. So this kind of underwater welding method, is the research focus and direction. But this method also has shortcomings, namely the flexibility and adaptability is poorer, welding time is long, the smoke thickened, affect visibility. Because often mobile location, weld joint quality is not guaranteed.