Before welding the tube can be preheated with oxygen-acetylene torch heating, resistance heating and induction heating method, in which resistance heating and induction heating temperature than the use of torch heating easier to control.
The tube is preheated, its role is to ensure that the welding heat input weld, rather than discharged into the surrounding metal, so as to avoid welding defects. Preheating, the welding zone and the surrounding metal is heated to 40 a 150 ℃, can well prevent the welding heat to the surrounding metal.
Since preheating reduces the temperature difference between the weld and the surrounding metal, the thermal stress of the weld metal is also reduced, reducing the tendency to weld cracking and deformation. In addition, preheating helps to eliminate gas, especially in the weld Spilled hydrogen. In the welding procedure, according to the welding method used, welding rod and tube material, etc., on the required preheating temperature are regulated. Preheat temperature can be measured using a high temperature thermometer, portable pyrometer or thermocouple.