Underwater welding is a metal joining process performed underwater. This method is primarily used in the repair of ships, maintenance of underwater pipelines, and construction of offshore platforms. Underwater welding applications were first initiated during World War I by the British Navy. The techniques employed during that period generally involved rudimentary procedures using bare electrodes wrapped in waterproofing materials.

Today, underwater welding is widely used not only for repair and maintenance but also for the construction of new structures. In particular, with the growing significance of submarine natural gas and oil pipelines, this technology plays a strategic role on an international scale.

^{Visual Representation of the Underwater Welding Process (Generated by Artificial Intelligence)}

Classification

Underwater welding is divided into two main categories: wet welding and dry welding.

• Wet underwater welding is a method in which the welding process is carried out directly in the water environment. In this technique, the weld pool remains in contact with the surrounding water.
• Dry underwater welding, on the other hand, is performed in pressurized chambers or enclosures where the welding area is mechanically isolated from water. By preventing water contact with the weld zone, dry welding provides a more controlled welding environment.

Although wet welding methods are more commonly used due to their lower equipment cost and operational simplicity, the direct exposure of the weld seam to water in this technique can negatively affect the quality and mechanical properties of the weld.

Areas of Use

Underwater welding is a joining method utilized in various industrial applications. It is employed in the repair of submerged sections of ship hulls, the installation of sacrificial anodes for corrosion protection, the laying and maintenance of underwater pipelines, and the construction of offshore oil and natural gas platforms. Additionally, it is preferred for external structural work on large vessels without the need for dry docking and for rapid repairs in emergency situations. These applications make underwater welding a functional technique for the maritime, energy, and construction industries.

Methods and Electrode Types Used

The most common underwater welding method is shielded metal arc welding (SMAW). In addition, flux-cored arc welding (FCAW), gas metal arc welding (GMAW/MIG-MAG), TIG welding, and plasma arc welding are also used at various depths and in different application contexts.

In wet welding, the most commonly preferred electrode type is rutile coated electrodes. These electrodes provide good arc stability, low spatter, and satisfactory weld bead appearance. Basic and cellulose-coated electrodes are not preferred in underwater welding due to intense gas release and difficulties in slag control.

Coated electrodes are insulated with waterproof coatings. Materials such as paraffin, cellulose varnish, or vinyl coatings are used for this insulation. In particular, paraffin coatings are effective in reducing the amount of diffusible hydrogen that may form during welding.

Material Properties and Microstructure

The most commonly used materials in underwater welding are low-carbon steels. These materials possess a low carbon equivalent (typically less than 0.3%) and are more resistant to hydrogen-induced cracking. In underwater welding, the cooling rate is significantly high. This leads to the formation of columnar crystals in the weld zone and the narrowing of the heat-affected zone (HAZ).

Experimental studies have shown that samples welded underwater exhibit higher hardness values (by approximately 6–8%) compared to those welded in atmospheric conditions, but they also show lower ductility (48% less elongation) and reduced impact toughness (14–22% lower).

Effect of Depth and Mechanical Results

The depth at which the welding process is conducted directly affects the quality of the weld. As depth increases, the cooling rate also increases. This can lead to changes in the microstructure of the weld metal, a narrowing of the HAZ, and degradation of certain mechanical properties. For example, in welds performed at a depth of 16 meters, the HAZ width was measured to be 40% narrower than that of welds made in atmospheric conditions.

However, some experimental studies have shown that there is no significant difference between the yield and tensile strength of welds performed in atmospheric and underwater environments, although the ductility of underwater welds is notably lower.

Safety and Operational Challenges

Underwater welding poses challenges not only technically but also in terms of safety. The individual performing the operation must be both a qualified welder and a professional diver. As depth increases, physical conditions such as pressure, limited visibility, light refraction, and heat transfer make the welding process more complex.

Vapor, gas, and fume bubbles can obstruct the welder's view. Furthermore, the rapid cooling of molten metal in water may adversely affect the quality of the weld bead. Gas bubbles formed during welding create a gas pocket around the weld pool, which can cause uncontrolled movement of metal droplets.

Equipment and Power Systems

An underwater welder must be equipped with a sealed helmet, special viewing glass, insulated electrode holders, and isolated power connections. Direct current generators with a capacity of approximately 300 amperes are typically used. For electrical safety, all circuits outside the welding circuit must be controlled by a circuit breaker.

Direct current (DC) power sources are generally preferred. Due to the conductivity of saltwater, current losses of up to 20% may occur underwater; therefore, current and voltage settings must be adjusted to account for these losses.

Advantages and Disadvantages

Advantages

• Enables rapid and on-site repairs in emergency situations.
• Allows the repair of large structures such as platforms or ships without the need to remove them from the water.
• Can be implemented with low equipment cost (especially in wet welding).
• In some operations, the use of a closed welding chamber (habitat) can improve weld quality.

Disadvantages

• Welders must be both divers and certified welders.
• The hardness of the heat-affected zone (HAZ) is high, posing a risk of brittleness.
• Due to limited visibility and high cooling rates, weld quality may be low.
• Hydrogen diffusion increases with depth, raising the risk of cracking.

Underwater welding is a welding technique of strategic importance, particularly in fields such as maritime operations, offshore structures, and the construction and maintenance of energy infrastructure. Applied in two primary forms—wet and dry welding—this method involves various technical and safety-related challenges. The most commonly used method, shielded metal arc welding, is preferred for its simplicity and applicability; however, it presents certain limitations compared to atmospheric welding in terms of weld quality, ductility, and impact toughness. In particular, the high cooling rate leads to microstructural changes and the formation of narrow heat-affected zones. The coating characteristics, water resistance, and chemical composition of the electrodes used have a direct impact on weld quality. Additionally, the requirement that the operator be both a certified welder and a trained diver increases the complexity of the procedure. Considering all these technical and environmental factors, underwater welding can yield reliable and functional results when performed with appropriate material selection, suitable parameters, and qualified personnel.