In various news stories or industrial videos, you’ve likely seen engineers and mechanics wearing huge helmets (or at least a pair of black goggles) and bending over a piece of metal with a gun-like tool that appears to shoot bright sparkles in every direction when it comes in contact with metal.
What they’re doing is ‘welding’ something. Welding is basically a process of joining objects using very high temperatures. Since it involves joining materials, typically thermoplastics or metals, by applying very high temperatures to a very small, specific point, it is a task that requires immense care, patience and precaution by the person performing it.
Welding is demanding enough in normal conditions, so what would it be like to weld underwater, where environmental conditions are so different than on land?
Welding at high pressures
Welding, like many other things, is best done on solid ground. However, there are certain conditions when you have to ‘take the plunge’ and weld underwater. Making repairs to deep-sea pipelines, mending the hulls of ships, and working on other marine structures are some of the instances when underwater welding is unavoidable.
High-pressure underwater welding (technically referred to as ‘hyperbaric fabrication‘) can be classified in two different types: dry welding and wet welding.
Dry welding is carried out in an enclosed chamber that is filled with a gas mixture and sealed around the structure that is being welded. This ‘habitat’ has slightly more pressure than the pressure at the surface (0.007 pounds per square inch more), but it’s not too significant.
A standard working habitat can house one person, but larger habitats can comfortably house two to three people. Therefore, people can work inside the enclosed chamber without being constantly exposed to water (as is the case with wet welding). The Deep Rover submersible is a great example of a dry welder. It can carry out welding projects up to 3000 feet underwater.
Gas tungsten arc welding – a welding process that uses a tungsten electrode to produce the weld – is the most popular dry welding technique. Generally speaking, dry welding provides better results in terms of the quality and precision of the weld.
Wet welding is performed while the worker is submerged, and therefore in constant contact with water. Shielded Metal Arc Welding (SMAW) is the most common wet welding technique.
Wet welding involves using an electric welding rod through which electric current passes. Since electric current and water are not typically friendly, the rod is protected by a waterproof flux. High-temperature sparks fly off the electrode to the weld area, forming an arc between the filler and base material. Metal is melted by temperatures up to 3500 degrees Celsius, so any cracks in the damaged object are filled by the melted material from the flux and steel.
With all that water surrounding both the welding equipment and the object being welded, it’s quite logical to think that welding would get disrupted by all that water surrounding the weld area.
Fortunately, it doesn’t, thanks to the ingenious design of modern welding equipment. When the weld area is heated at such high temperatures by burning flux, carbon dioxide is released as a byproduct. This forms a small bubble around the weld area, which creates a temporary shield that holds back any water from coming in contact with the welding spot.
Underwater welding can be very helpful, especially when a marine structure (like a ship, a pipeline or an oil rig) needs immediate maintenance. Therefore, if you happen to be riding along in a submarine that develops a minor breach while still submerged and far from the harbor, just be thankful that underwater welding is a thing!