Electric heat-welding process

This is a manual welding process which consists of heating and softening the two surfaces to he joined and a filler rod, usually of the same material, until complete fusion takes place. It is a similar process to welding metal, except that a naked flame is not used as this would burn the plastics material. Instead a stream of hot gas is used, directed from a special welding torch. The heat source may be electric or gas, at a temperature around 300 °C. 

TIG welding is an arc fusion welding process in which intense heat is produced by an electric arc between a non-consumable, torch-held tungsten electrode and a work piece see Fig. 8.117. 

Stress relieving is accomplished by heating the fabricated section in a special furnace. Alternatively, process equipment may be stress relieved in the field by electrical heating. The operating engineer should insist that replacement welded carbon steel piping be stress relieved if caustic can enter the piping system. 

Electric-welded pipe is defined as pipe having one longitudinal seam formed hy electric-flash welding or electric-resistance welding, without the addition of extraneous metal. The weld seam of electric-welded pipe should he heat treated after welding to a minimum temperature of 538 °C (1000 °F), or processed in such a manner that no untempered martensite remains. 

In arc welding, the coalescence of metals is achieved through the intense heat of an electric arc, which is estabUshed between the base metal and an electrode. The processes Hsted in Table 1 are differentiated by various means of shielding the arc from the atmosphere (1 3). 

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