Underwater welding (wet welding) is described as welding at ambient pressure with the weldeddiver in the water with no physical barrier between the water and the welding arc. Although it is a complex metallurgical process, wet welding closely resembles welding in air in that the welding arc and molten metal are shielded from the environment (water or dir) by gas and slag produced by decomposition of dux coated electrodes or flux cored wire. Underwater dry welding is done at ambient pressure in a chamber from which water has been displaced. Depending on the size and configuration of the chamber, the weldeddiver may be completely in the chamber, or only partially in the chamber, and may work in conventional welder’s attire, dive gear, or a combination of both.
Underwater welding has been used during the installation of new offshore drilling structures, sub-sea pipelines and hot taps, docks and harbor facilities, and for modifications and additions to underwater structures. However, underwater welding is most often required for repairs to existing structures. Maintenance and repair applications include:
(1) Replacement of damaged sub-sea pipeline sections and pipeline manifolds
(2) Replacement of structural members damaged by corrosion and fatigue
(3) Damage occurring during installation, boat collisions, or other accidental damage.
Specifications for underwater welding are published by American Welding Society, Miami, Florida; in ANSUAWS D3.6-93, Specification for Underwater Welding.