Underwater welding process in a nutshell
There are three main types of underwater welding used in the industry for many years. They are the wet underwater welding, coffer dam welding and hyperbaric welding.
In wet underwater welding, the Metal Arc Welding (MAW) is the most common process. For deep water repair, the friction welding is of great use. This is because it has the advantage of being relatively insensitive to depth and lends itself to robotic operation. In the former Soviet Union, the flux core arc welder (FCAW) had been widely used. The coffer dam welding is carried out in the dry in air. A rigid steel structure to house the welders would be sealed against the side of the structure to be welded. This would be open to the atmosphere. In hyperbaric welding a chamber would be sealed around the structure to be welded and is filled with a gas at the prevailing pressure. Helium containing 0.5 bar of oxygen is usually used as the gas.
The welder or diver would be usually works from outside the enclosure. He welds with each of several electrodes in turn, each electrode having been positioned in advance through a flexible port. The advanced welding technology involves the fabrication of a transparent enclosure around the intended weld. An appropriate gas is introduced to exclude water. Underwater welding offers a great deal of use for assembly or repair underwater. It has found to be more effective compared to the alternatives like clamped and grouted repairs. Wet underwater welding has been widely used in the repair of offshore platforms.