For many years pipe was generally joined with threaded fittings. Improved welding techniques gradually caused a trend toward welded joints. Today, welded piping systems are specified in a wide variety of industries, including power, refrigeration, chemical, petroleum, industrial gas and air, and food processing.
oxyfuel gas welding with oxyhydrogen or oxyacetylene was initially used for aluminium pipe. This process required the use of fluxes which had to be removed subsequent to welding, since they were a corrosion hazard to the pipe in the presence of moisture. Furthermore, welding, other than in the flat position, was very difficult. Both factors imposed a severe limitation on welded aluminium piping systems.
The development of the gas tungsten arc welding process (GTAW) during World War II provided a practical solution to the problem associated with oxyfuel gas welding aluminium pipe. The corrosion hazard resulting from the flux was eliminated by the inert gas shield and all-position welding techniques were developed. Subsequently, the gas metal arc welding process (GMAW) was developed and provided a substancial reduction in pipe welding time for application where this process was suitable.
Jorge T. Reyna´s Blog (NDT, Welding, Concrete & Coatings)