Interesting Jobs: Welding Underwater
Thursday, September 11, 2014 1:29:40 PM Australia/Sydney
'Underwater Welding' might sound like an oxymoron, but it's actually an incredibly important part of the industry and is one of the most difficult welding techniques.
Hyperbaric welding refers to the process of welding inside a highly pressurised environment; though this can also refer to dry atmospheres, it is mostly used in an underwater context. How underwater welding works, in a nutshell, is by replicating a dry environment. This is can be done by creating an artificial bubble or employing an entire chamber that removes water from the welding area. It's a dangerous job, but one that is extremely important for a number of water-related jobs. The most common metal welded is steel, as many other types of metal do not perform well at extreme depths.
Underwater welding has a large number of practical applications, the most prominent of these being underwater construction. Ships, piers and any structure built over water cannot always simply be assembled in a dry atmosphere and transported to water. In particular, repairs on existing underwater projects have to be welded where they are, which is where underwater welding comes in.
How it works
The overall process is more or less the same as arc welding, in that a current is generated by electrodes that melds two or more pieces of metal. The electrodes used in hyperbaric welding must be waterproof. The welder spends the entire time underwater, sometimes deep enough to require de-pressurizing before returning to dry land. How underwater welding works from a heat perspective can be explained by the type of gas.
In the first method, the diver carries with them a tank of gas, usually argon or nitrogen, and creates a bubble around the welding area. This creates a small dry zone, after which the welding can be completed as normal. The difficulty with this type of welding mainly lies in maintaining this bubble, as if it collapses, it will extinguish the arc. Underwater welding therefore requires a steady hand; combined with the usual techniques of welding effectively, it's easy to see why welding underwater is regarded as far more difficult than doing so on land. Another option is a hyperbaric chamber, which is a special chamber that is pressurised and pumps water out, allowing for a dry atmosphere even deep underwater.
The two options of dry and wet welding depend on a number of factors. Wet welding is a cheaper procedure, does not require as much special equipment (notably, the chamber) and can be set up more easily. However, its free-standing position means that the danger is much higher, and visibility lower. It is therefore a more common option for quicker jobs, closer to the surface. The materials in a wet weld are also limited to certain types of steel.
Dry welding, using the chamber, is more common and used on larger projects. It may be more costly, but as it creates an atmosphere that removes most of the water, the welding process becomes easier. Visibilty is increased, and the more stable atmosphere leads to a greater strength of weld. It's easy to see why this type would be used for bigger, more important projects, though dry or wet simply depends on the circumstance and the job required.
Stick welding is most commonly used underwater, and the electrodes are specially insulated to avoid electric shock to the user.
Quite a few welding techniques are unavailable underwater, such as pre-heating or applying hydrogen embrittlement. Therefore the process of achieving an effective underwater weld becomes even more difficult. Due to the surrounding water, rapid cooling is one of the biggest problems during the process.
To work underwater, a person must be certified as both a welder and a commercial diver. Though these two skills are important, underwater welding as a skill is an art unto itself, making it one that can only be mastered with training and practice. Notably, welding underwater is much more dangerous than its counterpart, due to the high-pressure atmosphere.
As previously mentioned, the equipment used during underwater construction must be completely insulated. Quite a few volts worth of electricity are used in the welding process, and the surrounding water greatly increases the risk of injury. The equipment may be highly specialised, but a gap in protective clothing or faulty wiring can lead to an electric shock to the welder.
The job is also dangerous from a pressure perspective, as some welds can potentially take place thousands of feet underwater. Some divers spend days underwater on a job, sleeping near the chamber, and this can lead to decompression sickness (or 'the bends') when surfacing.
The underwater atmosphere can also cause musculoskeletal issues, as well as the threat of ocean life. However, all of these dangers can be prevented through proper procedure. Welding is necessary to underwater construction, and this means that welders are required to enter potentially dangerous environments in order to get the job done.