Although underwater welding does not have as many applications in marine salvage operations as underwater cutting, underwater welding is an extremely important and useful process. By substituting welding for mechanical methods of joining, the overall cost and time spent on the job can be reduced considerably. Historically, most underwater welding was done for the purpose of making temporary repairs to waterborne ships. Specific wet and dry underwater welding techniques applicable to ship husbandry are properly addressed in the Underwater Welding Ship Husbandry Manual. This manual addresses basic welding techniques and their application to salvage operations. The joining of padeyes and patches onto recoverable objects are typical examples of underwater salvage welding.
Until mid-1960, all underwater welding consisted of wet welds. The technique was usually limited to the shielded metal arc process (commonly known as stick welding). Wet welding is a situation where both work and welder are in contact with the water. Today there are two additional underwater welding methods available. While each technique has individual merits and limitations, both share one common factor: water is not in direct contact with the weld area. In a sense, the welding is dry.
Dry underwater welding involves the weld being performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded.
The advantages of underwater welding are largely of an economic nature, because underwater welding for marine maintenance and repair jobs bypasses the need to pull the structure out of the sea and saves valuable time and dry docking costs. It is also an important technique for emergency repairs which allow the damaged structure to be safely transported to dry facilities for permanent repair or scrapping.