Underwater welding

Dry hyperbaric welding is used in preference to wet underwater welding when high quality welds are required because of the increased control over conditions which can be exerted, such as through application of prior and post weld heat treatments. This improved environmental control leads directly to improved process performance and a generally much higher quality weld than a comparative wet weld. Thus, when a very high quality weld is required, dry hyperbaric welding is normally utilized. Research into using dry hyperbaric welding at depths of up to is ongoing.^[3] In general, assuring the integrity of underwater welds can be difficult (but is possible using various nondestructive testing applications), especially for wet underwater welds, because defects are difficult to detect if the defects are beneath the surface of the weld.

Underwater hyperbaric welding was invented by a Russian metallurgist Konstantin Khrenov in 1932.

Dry

Dry hyperbaric welding involves the weld being performed at the prevailing pressure in a chamber filled with a gas mixture sealed around the structure being welded.

Most welding processes SMAW, FCAW, GTAW, GMAW, PAW could be operated at hyperbaric pressures, but all suffer as the pressure increases.^[4] Gas tungsten arc welding is most commonly used. The degradation is associated with physical changes of the arc behaviour as the gas flow regime around the arc changes and the arc roots contract and become more mobile. Of note is a dramatic increase in arc voltage which is associated with the increase in pressure. Overall a degradation in capability and efficiency results as the pressure increases.

Special control techniques have been applied which have allowed welding down to 2500m simulated water depth in the laboratory, but dry hyperbaric welding has thus far been limited operationally to less than 400m water depth by the physiological capability of divers to operate the welding equipment at high pressures and practical considerations concerning construction of an automated pressure / welding chamber at depth.^[5]

Wet

Wet underwater welding commonly uses a variation of shielded metal arc welding, employing a waterproof electrode.^[2] Other processes that are used include flux-cored arc welding and friction welding.^[2] In each of these cases, the welding power supply is connected to the welding equipment through cables and hoses. The process is generally limited to low carbon equivalent steels, especially at greater depths, because of hydrogen-caused cracking.^[2]

Risks

The risks of underwater welding include the risk of electric shock to the welder. To prevent this, the welding equipment must be adaptable to a marine environment, properly insulated and the welding current must be controlled. Commercial divers must also consider the safety issues that normal divers face; most notably, the risk of decompression sickness following saturation diving due to the increased pressure of inhaled breathing gases.^[6] Another risk, generally limited to wet underwater welding, is the buildup of hydrogen and oxygen pockets, because these are potentially explosive. Many divers have reported a metallic taste that is related to the breakdown of dental amalgam.^[7][8][9] There may also be long term cognitive and possibly musculoskeletal effects associated with underwater welding.^[10]

See also

• Welding
• Oxy-fuel welding and cutting

References

External links

• Health and Safety Executive - Performs research on long term health effects from underwater welding.
• Process overview at The Welding Institute

sv:Hyperbarisk svetsning

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