Hyperbaric welding

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Hyperbaric welding is the process of welding at elevated pressures, normally underwater. Hyperbaric welding can take place in the wet of the surrounding water or inside a specially constructed pressure chamber and hence a 'dry' environment. It is predominantly referred to as "Hyperbaric Welding" when used in dry mode, and is used in preference to wet welding 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 utilised.

[edit] Limitations

Most welding processes SMAW, FCAW, GTAW, GMAW, PAW can be operated at hyperbaric pressures, but all suffer as the pressure increases. 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.

[edit] References

Richardson, I M, Properties of the constricted gas Tungsten (Plasma) Arc at Elevated Pressures, Ph.D. Thesis, Cranfield University, UK, 1991

Hart, P R, A Study of non-consumable welding processes for diverless deepwater hyperbaric welding to 2500m water depth, Ph.D. Thesis, Cranfield University, UK, 1999