Welding is the fusing of metals together by a localised melting and filling process . Both permanent and temporary repairs may be made using underwater welding tools. Many marine salvage operations have only been made possible due to the development of welding processes. There are many different types of welding in use to-day above the water line , including Oxy-acetylene, resistance , brazing , soldering thermite , flash welding and electric arc welding. Only the latter though has found a place in underwater work .

There are a number of pieces of equipment which make up the welding set . A welding generator , normally producing 200 amps or more , will be required. AC not usually recommended due to the more dangerous nature of AC Voltage.
A safety switch or Diver's electric knife will be required topside . This must be permanently manned when in the closed (or live) position . The switch will be kept open at all times except whist welding is in progress. The knife may be single pole or 200 amp capacity or double pole for currents up to 400 amps.

The welding cable carries the current to the diver and is generally in lengths of 50 feet. There is a short length connected to the holder which is usually 10 feet long. The ends of the cable are joined using lugs and copious amounts of electrical insulating tape. The welding electrode holder must be well insulated and robust and must be of the quick change type to allow the diver to change the rod easily. The clamp is used to earth the work piece and is connected to the 'ground or' earth' .

A wire brush and chipping hammer are used to clean the material. The welding electrode is is thick wire , covered with flux , and underwater electrodes given the number 60 The coating most favoured in the 1950 s was Sealac and Ucilon. This was made up by a mixture of acetone and celluloid. Acetone being very flammable extreme must be taken when making up the solution .
An eye shield is required to protect the eyes from 'burning' with the intense light given off by the 6000 C core. Rubber gloves are also required and must be waterproof .

A chaffing suit is a useful addition whilst working with welding equipment. Lastly and very important a signalling device, usually a rope to indicate to the tender topside when to turn the current on or off as this occurs frequently when welding is in progress.