In underwater welding, the installation of large patches, as well as the attachment of suitable pad-eyes presents a more complicated problem to the diver than does underwater cutting. Considerable practice is necessary to achieve a consistently good standard of underwater welding for salvage work. As a result, the diver’s underwater welding techniques must conform to acceptable standards. Also, the ocean acts as a large heat sink and draws off the heat of the electrode. This may cause blow holes and possible loss of strength between the patch and hull. This is true because the gas cannot escape from the molten pool of metal due to sudden cooling by the surrounding water. Despite the above shortfalls, underwater welds of good strength that are acceptable for salvage work are possible. Unless otherwise specified, the term “underwater welding” as used in this manual refers to the wet welding technique where no mechanical barrier separates the welding arc from the surrounding water. Two types of welding to be covered here are: • wet welding and • dry welding at the “splash zone.”
Shielded metal arc welding is the most widely used process for wet welding. Specific welding procedures for underwater maintenance work on ships is addressed in the Underwater Ship-Husbandry.
Wet welding is accomplished with both the diver and the work completely submerged.
Dry welding at the “splash zone” is generally conducted in a dry box or cofferdam at atmospheric pressure. It is essentially conventional welding and is discussed in another article to provide the salvor with methods to exclude water from the weld area.