Underwater welding techniques are most commonly used
in executing marine engineering projects such as installation of oil
and gas rigs. Underwater welding is mostly related to welding work
pieces made from different types of metals such as steel, aluminum,
copper, and others.
Underwater welding can be classified
according to the type of equipment used and the type of processes
followed. The most common underwater welding process is known as manual
metal arc welding (MMA) which has the advantage of being relatively
insensitive to depth. This makes it the most suited technique for
undertaking deep-water repair activities.
Cofferdam welding
involves the use of a rigid structure to house the welders, which is
sealed against the side of the structure to be welded. Another type of
underwater welding technique is commonly known as Hyperbaric welding in
which an enclosure is sealed around the structure to be welded, and is
filled with a gas (commonly helium containing 0.5 bar of oxygen) at the
prevailing pressure. This welding technique is often combined with MMA
(SMA), TIG (GTA), or FCAW for effecting high integrity welds,
particularly for deep-water welds, including tie-ins in pipelines and
risers in the oil and gas industries.
Underwater welding
techniques are used for welding steel pipelines, other offshore
structures, submerged parts of large ships, and underwater structures
supporting a harbor. Welding in depths of 500 to 1000 meters generates
high weld metal diffusible hydrogen, which can increase the risk of
hydrogen-assisted cracking. This can be prevented with the use of
electrode coating formulations and improved power source technology.
Underwater
welding techniques can be dangerous if proper procedures and equipment
is not used. An underwater welder faces the potential risk from
electric shocks and from nitrogen introduced into the bloodstream
during exposure to air at increased pressure. Underwater welding safety
measures include emergency air or gas supply, stand-by divers, and
decompression chambers to avoid decompression sickness following rapid
surfacing after saturation diving.