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  • Hyperbaric welding

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    Underwater welding. Hyperbaric welding is the process of welding at elevated pressures, normally underwater. Hyperbaric welding can either take place wet in the water itself or dry inside a specially constructed positive pressure enclosure and hence a dry environment. It is predominantly referred to as "hyperbaric welding" when used in a dry environment, and "underwater welding" when in a wet environment. The applications of hyperbaric welding are diverse—it is often used to repair ships, offshore oil platforms, and pipelines. Steel is the most common material welded. Dry 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. 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 the Russian metallurgist Konstantin Khrenov in 1932.

  • Construction of the Trans-Alaska Pipeline System

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    The construction of the Trans-Alaska Pipeline System included over of oil pipeline, 12 pump stations, and a new tanker port. Built largely on permafrost during 1975–77 between Prudhoe Bay and Valdez, Alaska, the $8 billion effort required tens of thousands of people, often working in extreme temperatures and conditions; the invention of specialized construction techniques; and the construction of a new road, the Dalton Highway. The first section of pipe was laid in 1975 after more than five years of legal and political arguments. Allegations of faulty welds drew intense scrutiny from local and national observers. A culture grew around the unique working conditions involved in constructing the pipeline, and each union that worked on the project had a different function and stereotype. Thirty-two Alyeska Pipeline Service Company employees and contract workers were killed during the project. The main construction effort lasted until 1977; the first barrel of oil was delivered on July 28 of that year. Several more pump stations, added as oil flow increased, were completed through 1980.

  • Saturation diving

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    USS Monitor wreck at 70 m (230 ft) depth. Saturation diver conducts deep sea salvage operations.Saturation diving is a diving technique that allows divers to reduce the risk of decompression sickness ("the bends") when they work at great depths for long periods of time. In saturation diving, the divers live in a pressurized environment, which can be a saturation system on the surface, or an ambient pressure underwater habitat when not in the water. Transfer to and from the pressurised surface living quarters to the equivalent depth is done in a closed, pressurised diving bell. This may be maintained for up to several weeks, and they are decompressed to surface pressure only once, at the end of their tour of duty. By limiting the number of decompressions in this way, the risk of decompression sickness is significantly reduced, and the time spent decompressing is minimised. It is a very specialized form of diving; of the 3,300 commercial divers employed in the United States in 2015, only 336 were saturation divers.

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