Underwater welding method and apparatus

Persistent compressive stresses sufficient to suppress hot cracking, reheat cracking and stress corrosion cracking are developed in welds containing alloys of plural materials by quenching of the weld after onset of solidification but while the weld remains soft or "mushy" at a temperature above the melting point of eutectic alloys which may form. Control of the time of quenching is preferably established during submerged welding by a cup-shaped exclusion fitting which is sized relative to the dimensions of a molten weld pool and the speed of travel of a welding heat source such as a plasma transfer arc torch. The cup-shaped exclusion fitting provides improved protection of the weld and heat source with inert gas supplied thereto while also permitting submerged welding at higher hydrostatic pressures than has heretofore been possible. An improved apparatus for transport of powdered welding materials provides for bleeding off of a portion of a flow of transport gas used to transport the powdered materials and can thus provide a reliable supply of such materials over increased distances and against increased gas pressures without compromising the welding heat source or the quality of the weld.