DS Articles

Underwater welding refers to a number of very different processes. However, all of them do have one thing in common - they’re done below the surface of the water.

There are lots of different applications out there for using underwater welding. The material most commonly welded is steel, but that steel might make up an offshore oil platform, pipeline, or a ship.

Underwater welding comes in two basic categories - wet and dry. Both of them are considered hyperbaric welding, since they’re performed at relatively high pressures. Dry welding is the most common technique for deep water welding, or any other application where strength is very important.

The problem with many dry underwater welding methods is that they are expensive and require building full hyperbaric chambers to enclose the equipment and the welder. There are alternative methods being developed, where a smaller chamber encompasses only the area to be welded. These could make this type of welding the best choice for almost any application.

Usually considered superior to wet welding, dry welding is used whenever it’s economically feasible and doesn’t use too much time. Wet welding isn’t as strong, and may create oxygen and hydrogen pockets, and dangers of explosion. Wet underwater welds are often temporary, and must be replaced relatively quickly.

The depth limitations of welding underwater may vary - for instance there’s ongoing research into using dry techniques as deep as 1000 meters. Projects that use NEPSYS type welding have been successfully performed deeper than 30 meters, and the systems themselves are tested to 80 meters. SAT diving is required if the weld is deeper than 50 meters, however.

The mechanical properties of dry welds tend to be much better than those of wet welds - they are a permanent part of the structure. Dry welding typically achieves more than a twenty percent elongation of the weld when tested to destruction. By comparison, wet welding is rated to only seventeen percent, and usually achieves only seven to ten percent.

Wet underwater welds are usually used when conventional dry welding is too time costly or too expensive. The use of hyperbaric chambers in dry welding can also cause hydrogen absorption problems, due to humidity levels.

Alternative methods using a NEPSYS dry welding system are less expensive, and there’s no concern about humidity and hydrogen absorption. These chambers take less time to construct, making this kind of dry underwater welding less time consuming.

Another kind of dry underwater welding, called a cofferdam repair, is useful but doesn’t remove moisture and humidity. That means that these repairs have similar problems with hydrogen absorption to those found in welds using hyperbaric chambers. The way to avoid this involves using heated inert gas to fill the enclosure around the weld.

This gas is pressurized to one unit more than the surrounding water, which is sufficient to keep the water out of the chamber. The chamber does not need to be larger than the area to be welded, minimizing costs and transport problems. Since the chamber is filled with inert gas, quenching of the weld is also not a problem.

Underwater welding is a vital part of many industries. Anyone who needs to work around underwater structures should know all their underwater repair options, including any dry welding techniques that might be appropriate. That knowledge will help you choose the correct one for your needs.