Kinds of Underwater Welding:

There are three kinds of underwater welding. These are wet underwater welding, coffer dam welding, and hyperbaric welding. Each kind is completely unique from the others and has specific processes that have to be followed.

Wet underwater welding is done using the manual metal arc welding (MMA) process most commonly. Flux-cored arc welding (FCAW) used to be used in the former Soviet Union. Friction welding has a lot of potential to be used in deep water repair, especially if something needs to be repaired where people can't go. It mainly is done using robots.

Coffer dam welding consists of a steel structure that is sealed against the side of the structure that needs to be welded. It is open to the atmosphere and houses the welders in dry air, making it easier to do the welds.

Hyperbaric welding is done by sealing a chamber around the structure to be welded, and then filling it with gas. Helium is commonly used. The gas fills the chamber to a higher pressure than the water around and pushes the water out. More recently, transparent enclosures around the area to be welded are being used. The welder/diver then welds using several MMA electrodes in turn. They work from outside the chamber and the electrodes are already positioned through a flexible port in advance. The enclosures are made for every joint needing to be welded, and this process costs much less than the conventional method of making a large chamber.