How Much Do You Know About Submerged Arc Welding?

Recently, a video from the official抖音 account of underwater operations has gained widespread attention. Welders have been enthusiastically leaving comments, showing great curiosity about underwater welding. Today, the editor is joining the team to learn about underwater welding.

In 1802, a scholar named Humphrey noted that an electric arc could burn continuously underwater, which pointed out the possibility of underwater welding in marine engineering.

In 1917, welders at a British naval dockyard employed underwater welding techniques to seal the rivet gaps in a ship's underwater section that was leaking. This marked the first application of underwater welding.

In 1932, Khrenov invented the thick-film underwater welding rod.

In 1985, a batch of certified diving welders was produced, and a wet welding process for underwater operations at depths less than 100 meters was established.

In 1987, the underwater wet welding technique was applied in the repair of stainless steel pipelines in nuclear power plants.

Underwater welding presents a more complex process due to the presence of water, leading to various issues not encountered in land-based welding. Currently, there is a wide variety of underwater welding methods being applied and researched worldwide, with the most mature being arc welding.

Underwater Welding Operation Video:

Underwater welding and cutting are indispensable important techniques in the installation and maintenance of underwater engineering structures. They are commonly used in marine engineering projects such as sea rescue operations, ocean energy, and offshore mining, as well as the construction of large underwater facilities.

Underwater Welding Techniques

Dry Welding

This method involves enclosing the welding piece with a large gas chamber, where the welder performs the welding inside. Due to the welding taking place in a dry gas phase, the safety is relatively good. When the depth exceeds the air's penetration range, an increased pressure of local oxygen in the air environment can easily cause sparks. Therefore, inert or semi-inert gases should be used within the chamber. During dry welding, the welder should wear specialized flame-retardant and high-temperature-resistant protective clothing.

Local Dry Welding

Local dry welding is an underwater welding method where the welder performs welding in water while manually displacing the water around the welding area. The safety measures are similar to those of wet welding. Since local dry welding is still under research, its use is not yet widespread.

Wet-Film Soldering

Wet welding is a type of underwater welding where the welder performs the welding directly beneath the water, as opposed to manually removing the water around the welding area.

Arc welding under water, similar to submerged arc welding, occurs in bubbles. As the electrode burns, the coating on the electrode forms a sleeve that stabilizes the bubble, thus stabilizing the arc. To ensure stable burning of the electrode under water, a layer of paint with a certain thickness must be applied to the electrode core, and the electrode should be soaked in paraffin or other waterproof substances to achieve waterproof properties. The bubble consists of hydrogen, oxygen, water vapor, and bubbles produced by the burning of the electrode coating; and other oxides generated by the smoky mist. To overcome the difficulties of initiating and stabilizing the arc due to the cooling and pressure effects of water, the initiating voltage must be higher than the atmospheric initiating voltage, and the current should be 15% to 20% greater than the welding current in the atmosphere.

Underwater Welding Features

1. Poor visibility is present due to water's significantly stronger absorption, reflection, and refraction of light compared to air, resulting in rapid light attenuation when propagating through water. Additionally, during welding, a large number of bubbles and smoke are produced around the electric arc, severely reducing the visibility of underwater arcs. Underwater welding in silt-covered sea floors and sandy mud-laden waters exacerbates this poor visibility.

2. High hydrogen content in welds is a major enemy of welding. If the hydrogen content exceeds the permitted limit during welding, it can easily cause cracks and even lead to structural damage. Submerged arc welding generates thermal decomposition in the surrounding water, which increases the amount of hydrogen dissolved into the weld. The poor quality of焊接 joints in submerged arc welding and the high hydrogen content are inextricably linked.

3. The cooling rate is fast during underwater welding, as the thermal conductivity coefficient of seawater is approximately 20 times higher than that of air. When wet welding or local welding methods are used, the workpiece to be welded is directly immersed in water, resulting in a significant rapid cooling effect on the weld seam, which is prone to the formation of high-hardness quenching structures. Therefore, only dry welding can avoid the cooling effect.

As pressure increases, the arc column becomes thinner, the weld width narrows, the weld height increases, and the density of the conductive medium rises, thereby increasing the ionization difficulty. Consequently, the arc voltage rises and the arc stability decreases, leading to more spatter and dust.

5. Continuous operation is challenging to achieve due to the influence and limitations of underwater environments. As a result, in many cases, it is necessary to adopt a method of welding for a section, then stopping, leading to discontinuous weld seams.

Underwater Welding and Cutting Safety Measures

1. Conduct surveys of the environmental conditions in the work area, including weather, water depth, water temperature, and current velocity. Operations may only be conducted when the surface wind is less than 6 levels and the flow velocity at the work site is less than 0.1 to 0.3 m/s.

2. Prior to underwater welding and cutting, it is crucial to investigate the nature and structural characteristics of the item to be welded or cut, and determine if there are flammable, explosive, or toxic substances present within the work area. Properly secure any objects that may fall or collapse, especially during underwater cutting, to prevent injury or damage to the air supply tubes and cables.

Prior to submersion, on the water surface, inspect and test the insulation, watertightness, and technical performance of welding, cutting equipment and tools, diving gear, air supply pipes and cables, communication tools, and other equipment. Oxygen hoses must be cleaned with steam or hot water at 1.5 times the working pressure, ensuring no oil or grease adheres to the inside or outside. The air supply pipes and cables should be securely tied at intervals of 0.5 meters to prevent tangling. After entering the water and descending, promptly organize the air supply pipes, cables, and signal lines to ensure they are in a safe position to avoid damage.

Above the work area, within a radius equivalent to the water depth, no other operations are allowed to take place simultaneously. Due to the potential release of unburned gases or toxic substances during underwater operations that may rise to the surface, personnel on the surface should have fire prevention measures in place and the air supply pump should be located in the upwind position to prevent fire or for the protection of divers from inhaling toxic gases.

5. Prior to operation, the operator must ensure the work area is safely prepared by removing any surrounding obstructions. Underwater welding and cutting should not be performed while floating in the water; an operation platform must be installed beforehand, or a safe operation position must be selected on the object. This is to prevent the operator, diving gear, air supply pipes, and cables from being within the splash or flow range of molten slag.

6. Divers must have communication devices with surface support personnel. Only after all preparations are complete and with the consent of the support staff, can the welding and cutting operations begin.

7. Underwater welding and cutting operations must be performed by individuals who have undergone specialized training and hold the appropriate work license.