Before beginning any welding operation, the bevel of the pipe must be preheated to a temperature of at least 150°C (302°F) to avoid defects such as cracking and lack of fusion.
Both induction heating and resistance heating can be used for this purpose. Induction heating is the most efficient method for quick and repeated heating, as in the case of pipeline construction, while resistance heating is suitable for small joints.
Preheating is also required for the application of thermal insulating and heat-shrink materials on the pipe surface. With the use of specifically designed inductors (coils), induction heating is the most advisable method for this type of coating applications thanks to its performance, because it is easy to control, and it prevents oxidation of the sandblasted joint.