What Is The Difference Between Wet And Dry Underwater Welding? - Company News

Underwater welding, as a critical technology in marine engineering, offshore oil exploitation, and underwater infrastructure maintenance, is divided into two main categories: wet underwater welding and dry underwater welding. These two technologies differ significantly in operation environment, equipment, welding performance, and application scenarios. A clear understanding of their differences is crucial for selecting the appropriate welding method in practical projects.
Core Differences in Operation Environment
Wet Underwater Welding
In wet underwater welding, the welder and the welding zone are completely exposed to the water environment during the welding process. There is no isolation device between the welding operation and the surrounding water, and the welding arc directly burns in the water. The water temperature, pressure, and flow rate in the working area will directly affect the welding process. For example, in shallow sea areas with a water depth of 10–30 meters, the water pressure can reach 1–3 atmospheres, and the water flow may cause the arc to fluctuate, increasing the difficulty of welding.
Dry Underwater Welding
Dry underwater welding creates a dry or semi-dry working space for the welding area. A sealed chamber (such as a pressure vessel or habitat) is installed around the welding position, and water in the chamber is drained or replaced with inert gas (such as argon) to simulate a land-like welding environment. The welder can operate inside the chamber or control the welding robot remotely. The pressure in the chamber is usually balanced with the external water pressure to avoid structural damage to the chamber. For example, in deep-sea welding at a depth of 100 meters, the internal pressure of the chamber will be adjusted to 10 atmospheres to match the external water pressure.
Differences in Welding Equipment and Materials
Wet Underwater Welding
•Welding Power Source: Special DC power sources with high current stability are required to resist the interference of water on the arc. The output current is usually 300–600A, and the voltage is 20–40V, which can maintain the arc combustion in water.
•Electrode: Waterproof electrodes are used. The coating of these electrodes contains ingredients such as flux and gas-generating agents. When heated, the gas-generating agents release protective gases (such as carbon dioxide and hydrogen) to form a gas film around the arc, isolating part of the water. For example, E7018 underwater electrodes have a thick coating that can slow down the cooling rate of the molten pool.
•Welder's Equipment: The welder wears a diving suit, diving helmet, and waterproof gloves. The welding torch is designed to be waterproof and anti-electric shock, with an insulating layer to prevent current leakage.
Dry Underwater Welding
•Sealed Chamber System: This is the core equipment, including pressure-resistant shells, water pumps, gas control valves, and pressure sensors. The chamber is usually made of high-strength steel or titanium alloy to withstand high water pressure. For example, the dry welding chamber used in offshore oil platforms can achieve a pressure resistance of up to 50 atmospheres, adapting to deep-sea environments below 500 meters.
•Welding Equipment: It can use welding methods similar to those on land, such as shielded metal arc welding (SMAW) and gas metal arc welding (GMAW). The welding power source and torch do not need special waterproof treatment, but they need to be compatible with the pressure environment in the chamber.
•Auxiliary Systems: Inert gas supply systems (to maintain the dry environment in the chamber), temperature control systems (to prevent condensation), and video monitoring systems (to assist remote operation) are included.
Differences in Welding Performance and Quality
Wet Underwater Welding
•Arc Stability: The arc is easily disturbed by water flow and water vapor, resulting in unstable combustion. The cooling rate of the molten pool is extremely fast (about 10–100 times that of land welding), which may cause cold cracks in the weld.
•Weld Mechanical Properties: The tensile strength of the weld is usually 70%–80% of that of land welding, and the impact toughness is lower. For example, the impact energy of the weld metal in wet welding of carbon steel is generally 20–30J, which is significantly lower than 40–60J in land welding.
•Defect Rate: It is prone to defects such as pores (caused by water vapor entering the molten pool), incomplete fusion (caused by rapid cooling), and slag inclusion (caused by poor fluidity of the molten metal). The qualified rate of one-time welding is usually 60%–80%.
Dry Underwater Welding
•Arc Stability: The arc burns in a dry or inert gas environment, with stability close to that of land welding. The cooling rate of the molten pool is slow, which is conducive to the escape of gas and the floating of slag.
•Weld Mechanical Properties: The weld strength and toughness are close to those of land welding. For example, the tensile strength of the weld in dry welding of low-alloy steel can reach 90%–100% of that of land welding, and the impact energy can reach 35–50J.
•Defect Rate: The defect rate is low, and the one-time welding qualified rate can reach 90%–95%. Common defects are mainly caused by improper parameter setting, such as overheating or insufficient penetration.
Differences in Application Scenarios and Cost
Wet Underwater Welding
•Application Scope: Suitable for shallow water (usually within 50 meters) and non-critical structures, such as emergency repair of underwater pipelines, maintenance of river bridges, and welding of small underwater components. For example, when a 20-meter-deep water supply pipeline leaks, wet welding can be used for temporary plugging.
•Cost: The equipment investment is low (mainly diving equipment and special electrodes), and the construction cycle is short. The cost per meter of welding is usually 500–1,000 US dollars, which is suitable for projects with limited budgets.
•Advantages and Disadvantages: The advantage is flexibility and quick response; the disadvantage is poor welding quality and high requirements for welders' skills (they need to master both diving and welding technologies).
Dry Underwater Welding
•Application Scope: Suitable for deep water (more than 50 meters) and key structures, such as welding of offshore oil drilling platforms, installation of deep-sea pipelines, and maintenance of nuclear power plant underwater components. For example, the welding of 300-meter-deep oil pipeline connectors must use dry welding to ensure long-term reliability.
•Cost: The equipment investment is huge (the cost of a set of dry welding chamber system can reach millions of dollars), and the preparation work is complicated (such as chamber installation and pressure testing). The cost per meter of welding is 5,000–20,000 US dollars, which is only used in high-value projects.
•Advantages and Disadvantages: The advantage is high welding quality and stability, which can meet strict engineering standards; the disadvantage is poor flexibility and long construction cycle.
Selection Suggestions for Engineering Applications
Industry experts suggest that the choice between wet and dry underwater welding should be based on the following factors:
•Water Depth: Wet welding is preferred for shallow water within 50 meters, and dry welding is recommended for deep water exceeding 50 meters.
•Structural Importance: Key structures (such as oil platforms and nuclear power equipment) that require long-term safe operation must use dry welding; non-critical structures or temporary repairs can use wet welding.
•Budget and Construction Cycle: Wet welding is suitable for projects with tight budgets and urgent schedules; dry welding is chosen when quality is the primary consideration and the budget is sufficient.
•Welding Quality Requirements: If the weld needs to withstand high pressure, corrosion, or fatigue loads (such as submarine pipelines), dry welding is required; if only temporary connection is needed, wet welding can meet the requirements.
In conclusion, wet and dry underwater welding have their own characteristics and applicable scenarios. With the development of marine engineering, dry welding technology is constantly improving (such as the application of robot welding in chambers), while wet welding is also optimizing electrodes and processes to improve quality. In future underwater engineering, the two technologies will complement each other to provide technical support for the development and maintenance of underwater infrastructure.