Welding & Cutting Underwater
Underwater electric welding and cutting is an indispensable and important technological means in the installation, maintenance and construction of underwater engineering structures. They are often used in the construction of marine engineering and large underwater facilities, such as marine salvage, marine energy, marine mining, etc.
There are three types of underwater welding: dry method, wet method and local dry method.
（1） Dry welding
This is a method of using a large gas chamber to cover the weldment and the welder to weld in the gas chamber. As it is welded in the dry gas phase, its safety is good. When the depth exceeds the submergence range of air, it is easy to produce Mars due to the increased pressure of local oxygen in the air environment. Therefore, inert or semi inert gas shall be used in the gas chamber. During dry welding, welders shall wear special fireproof and high temperature resistant protective clothing.
Compared with wet and local dry welding, dry welding has the best safety, but it has great limitations and is not widely used.
（2） Local dry method
Local dry method is an underwater welding method in which the welder carries out welding in water, but artificially drains the water around the welding area. Its safety measures are similar to those of wet method.
As the local dry method is still under study, it is not widely used.
（3） Wet welding
Wet welding is an underwater welding method in which the welder directly performs welding under water, rather than artificially draining the water around the welding area.
The underwater combustion of arc is similar to that of submerged arc welding, which burns in bubbles. When the welding rod burns, the coating on the welding rod forms a sleeve to stabilize the existence of bubbles, thus stabilizing the arc. To make the welding rod burn stably under water, a layer of coating with a certain thickness must be coated on the core of the welding rod, and the method of impregnating with paraffin or other waterproof substances must be used to make the welding rod waterproof. Bubbles are generated by hydrogen, oxygen, water vapor and the combustion of electrode coating; Other oxides produced by turbid smoke. In order to overcome the difficulties of arc striking and stabilizing caused by water cooling and pressure, the arc striking voltage is higher than that in the atmosphere, and the current is 15% ~ 20% higher than that in the atmosphere.
Compared with dry welding and local dry welding, underwater wet welding has the most applications, but its safety is the worst. Due to the conductivity of water, preventing electric shock has become one of the main safety problems in wet welding.
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