Underwater Welding Technology: Classification And Applications

01 Introduction

Underwater welding is a core technology in marine resource development, ship maintenance, and subsea pipeline repair. It must be performed in extreme environments with high pressure, low temperatures, and low visibility. Due to the rapid cooling effect of water, the risk of hydrogen embrittlement, and environmental interference, the complexity and quality risks of underwater welding are significantly higher than those of land-based welding. Based on the welding environment and process characteristics, underwater welding is mainly classified into three types: wet welding, dry welding, and localized dry welding. Each technique has its unique principles, advantages, disadvantages, and applicable scenarios.

02 Wet Welding

Wet welding is the most fundamental underwater welding method, where the welder and arc are directly exposed to water. During welding, the high temperature of the arc instantly vaporizes the surrounding water, forming bubbles composed of water vapor, hydrogen, and oxygen that temporarily isolate the molten pool from water contact. This technique typically uses specialized waterproof electrodes, such as E6013 or nickel-based alloy electrodes.

The advantages of wet welding include high flexibility, low cost, and the ability to perform emergency repairs quickly in shallow water (within 30 meters) without requiring complex equipment. However, it also has notable drawbacks: the instability of the bubbles often leads to secondary contact between the molten pool and water, causing defects like porosity and hydrogen embrittlement. Additionally, as water depth increases (beyond 50 meters), water pressure significantly affects arc stability, making penetration control difficult. According to the Norwegian classification society, 70% of global ship emergency repairs rely on wet welding, especially in localized hull repairs and anchor chain welding.

03 Dry Welding

Dry welding completely isolates the welding environment from water to improve welding quality. This technique places the welding area inside a sealed high-pressure chamber, where inert gases (such as helium or argon) expel water and maintain pressure balance with the external water pressure, simulating land-based welding conditions.

Dry welding can use high-precision methods such as TIG and MIG, achieving weld tensile strength of over 90% of land-based welding and enabling applications in deep water environments (such as 3000-meter-deep subsea pipeline repairs). However, this technique has high equipment complexity and costs, requiring custom high-pressure chambers, gas circulation systems, and diving support platforms. A single operation can cost up to ten times that of wet welding. For example, in the North Sea oil field, dry welding successfully completed an all-position circumferential weld repair on an 800mm diameter subsea pipeline.

04 Localized Dry Welding

Localized dry welding is an intermediate solution between wet and dry welding, aiming to create small dry areas using localized water removal techniques. Common methods include water jet drainage and gas shielding: the former uses high-speed water flow to remove water from the welding zone, while the latter creates a protective gas barrier using compressed air or inert gas.

This technique significantly reduces weld hydrogen content (50% lower than wet welding) while avoiding the complex equipment requirements of dry welding. It is particularly suitable for confined spaces such as pipe joints and flanges. However, the success of localized dry welding highly depends on drainage stability; fluctuations in water flow or gas pressure can easily lead to molten pool contamination. Moreover, precise coordination between drainage and welding parameters is required. The titanium alloy robotic arm repair of China’s "Deep Sea Warrior" manned submersible was performed using the gas shielding method of localized dry welding.

05 Conclusion

Despite significant technological advancements, underwater welding still faces many challenges. Firstly, hydrogen atoms generated by water decomposition penetrate the weld, causing hydrogen-induced cracks that severely threaten structural integrity. Secondly, low underwater visibility makes weld positioning reliant on robots or sensors. Additionally, deep-sea high-pressure environments impose extreme precision requirements on welding robot motion control.

As marine development advances into deeper waters, the integration of new materials, robotics, and in-situ monitoring will drive underwater welding towards higher reliability and intelligence. Future development directions include the creation of intelligent welding robots, low-hydrogen welding materials (such as nano-coated welding wires to suppress hydrogen absorption), and multi-physics field collaborative monitoring systems (combining acoustics, spectroscopy, and electrical signals for real-time process parameter control).

**--Cite the article published by 高能束加工技术 on March 24, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."