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Underwater welding
From GAWDAwiki
Underwater welding is welding performed underwater either in wet or dry conditions. Dry underwater welding refers to underwater welding which is performed under hyperbaric conditions (an underwater habitat displaces the water with a gas at the prevailing pressure). Wet underwater welding refers to welding which is performed in fresh- or salt-water without a protecting habitat.
The most commonly used wet welding technique is shielded metal arc welding (SMAW), also known as manual metal arc (MMA) welding (stick welding). Wet welding is performed by using a power source generating DC current only (For wet welding, AC is not used due to electrical safety and difficulty in maintaining a welding arc underwater.); the inclusion of a single or dual pole knife switch (circuit breaker), which protects a welding diver from electrocution; and the use of double insulated cables. Both the power source and knife switch (capable of breaking the full wet welding current) are secured above water (grounded) and controlled (on the diver welder's command) by an operator. The cross section of the welding cable is adjusted to the length of the cable and should be highly wear resistant and sufficiently flexible; special welding electrode holders are used with extra insulation against the ingress of water.[1] [2]
Underwater welds (both wet and dry hyperbaric) are required to meet standards just like welds made above water. In the US the standards come under the direction of the ANSI / AWS D3.6b sub committee which is part of the ANSI / AWS D3 Committee for welding in Marine Construction. The current specification for underwater welding is the ANSI / AWS D3.6-93 Specification for Underwater Welding.[3]
