a process of welding through the spot melting of a metal by the flame of a gas-fed welding torch.

For higher flame temperature, a mixture of a gaseous fuel and industrially pure oxygen is used. Oxygen is usually kept in steel containers under a pressure of 15 meganewtons per sq m (150 kilograms-force per sq cm). Acetylene is the primary gaseous fuel used, because an oxyacetylene flame gives the highest temperature: 3100-3200° C. Other fuel gases such as hydrogen-oxygen and benzine-oxygen are employed only rarely in welding.

Acetylene is produced at the job site through the breakdown of calcium carbide by water in acetylene generators, or it is transported to the site dissolved in acetone in steel containers. Oxygen and acetylene are fed by hoses into a welding torch, where they are blended. Combustion occurs at the outlet of the welding tip, and a welding flame is created there. This flame simultaneously melts the edges of the parts being united and a welding rod of filler metal, creating a joint weld. Gas welding is used for steel, cast iron, copper, aluminum, and various alloys when the thickness of the parts to be welded ranges from 0.1 to 6 mm. It is used less frequently when the thickness reaches 40-50 mm, because in such cases other welding methods are cheaper and more convenient.

The surfacing of all sorts of parts by gas welding is also widely practiced. Gas welding is mechanized only slightly and is usually done by hand. Gas welding produces a weld of satisfactory quality. However, this process sometimes results in buckling of the welded parts, since a large area of the metal is heated. The advantages of gas welding are its portability and the low cost of welding apparatus. Its drawbacks are the high cost of operation and the danger of explosion. For the latter reasons, gas welding is being replaced by arc welding.