The need to perform underwater welding can be due to various reasons, usually related to construction work. For example, this may concern the installation of structures for hydroelectric stations, port groups, bridges, etc. Piping arrangements are also widespread. In any case, welding under water has been used for several years and the quality of the result is slightly inferior to standard techniques.
Principles of forming a welding arc under water
Different technological methods of organizing the welding process under water are used. Two methods are fundamentally distinguished: with the formation of an artificial gas environment and with the use of equipment provided with effective insulators from water. The most reliable and productive method is considered to be welding in a deep-sea chamber, which contains thewelder, and work unit. A dry environment is formed, which completely eliminates interference from moisture. Next, welding is carried out under water pressure with the connection of a pressure complex that provides communication supply to the chamber.
The quality of work meets the highest requirements, but it is technically difficult and expensive to organize such conditions. Only large enterprises working on large-scale projects can afford this. Therefore, the method of arc welding in a gas bubble, which is formed during the evaporation of water and molten metal elements, is more often used. The electrode coating will play an important role in this process.
Required Equipment and Materials
Welding can be done on both AC and DC. Equipment with consumables is selected for specific arc parameters with the expectation of providing protection against short circuits and loss of combustion stability. By the way, the average arc voltage should be 30-35 V. The power sources are single-station and multi-station devices, supplemented by a traditional combination of transformers (generators) and converters. The voltage of the units at idle should vary on average from 70 to 100 V.
Special attention is paid to the selection of electrodes. For welding under water in manual mode, rods with a thickness of 4-6 mm are used. But the most important thing is the characteristics of the electrode coating. At a minimum, it should be a waterproof layer impregnated with nitro-varnishes, paraffin, celluloid solutions in acetone and syntheticresins with dichloroethane. A diver-welder handles the electrode using a special electrode holder, provided with electrical insulation over the entire surface.
Hydrowelding instructions
Dry welding technology, in which the gaseous medium is localized. In the working area, a camera is mounted from portable modules that allow you to organize a dry isolated environment under water. Metal welding is performed as follows:
- The electrode wire is fed through the flexible hose that goes into the chamber.
- In parallel, the supply of inert gas begins, which will protect the welded area and the electrode coating.
- Welding diver adjusts the wire feed with a traction mechanism.
- Voltage is applied to the arc through current sources located on the surface.
- Using a working tool with an electrode holder, the operator starts the ignition of the arc and direct thermal impact on the metal.
A feature of this process in relation to conventional welding on land can be called the use of a wide group of instrumentation that allows you to comprehensively take into account the indicators of pressure, moisture and temperature in the chamber.
Wet welding instructions
By this method both manual and semi-automatic welding can be realized. When installing large structures, the overlapping technique is usually used, and typical thermal action operations allow you to providecorner, tee and butt joints of metal. How is it cooked under water by welding using this technology? The technique is based on the ability of an electric arc to maintain combustion in an artificially created gas bubble under conditions of active water cooling. The welder is in a special diving suit, receives equipment and the necessary eyeliners from equipment located on the surface. Further, the process is carried out according to standard arc welding technology. In semi-automatic mode, autonomous wire feeding is possible, which makes the workflow uninterrupted. However, this method has many drawbacks, including poor visibility, tightness of the arc, porous weld, etc.
Features of cold welding under water
This method eliminates the need for thermal action on the metal in order to ensure the melt. The principle of operation lies in the chemical processes that are activated by a special paste. These are one-component or two-component based formulations, which are a highly adhesive adhesive mixture. In particular, plastic and waterproof pastes with metal fillers are used for underwater welding. After the putty is completed, the composition is activated, providing a durable sealing of the working area. The main disadvantage of such welding can be called the limited application. This method is suitable only as a means of restoring minor damage in structures and pipelines. To connect massive metal elements, such mixtures are not strong enough.
Features of arc cutting
The workflow in this case is carried out under high welding current. In this case, the equipment can be used the same as in arc welding. It is desirable to use electrodes of a larger diameter - about 5-7 mm and up to 700 mm long. Cutting is performed as the electrode moves in the working area. It is recommended to start from a hole or edge, and then maintain a stable cutting contour until it ends. In the case of thick sheets of metal, electric arc welding under water is performed with a smooth movement from the top to the bottom, and fast - when lifting from the bottom up. The following feature is also taken into account: as the thickness of the workpiece increases, the productivity of the equipment in terms of electrothermal effects will sharply decrease. At the same time, the consumption of electrodes will increase significantly.
Difficulties in performing work from the position of a welder
Problems of working under water are caused by a whole range of factors. Among them are the already mentioned poor visibility, constraint of movement due to equipment and pressure, overcoming the underwater current and the lack of reliable reference points. All this affects the accuracy of electrode manipulation and equipment connection. The most common and characteristic welding defects under water include poor penetration, sagging and undercuts. There is also an increased risk of typical negative factors, from which the surface is traditionally protected by flux and gas insulating media.
Conclusion
The success of underwater welding operations to the greatest extent will depend on the quality of their technical organization. Even the choice of the method of thermal exposure is not so important, since all methods are based to varying degrees on the principle of ignition and maintenance of an electric arc. Unless welding under water using synthetic sealant pastes has fundamental differences, although it is used in exceptional cases. But even with this method, it is important to take into account the smallest organizational details. These include the quality of the working equipment, the accuracy of the preparatory operations and the coherence of the actions of all members of the installation team. It is important to emphasize that underwater welding requires the participation of a whole group of specialists in addition to the diver. Most often, the working equipment remains on the surface and a significant part of the control and regulation operations is carried out by electromechanics without the participation of a welder.
