How To Preheat Metal Before Welding. When the temperature outside is very low or the plate is cold preheating can help prevent defects. The minimum temperature to be ensured just before the commencement of weld.
Inter-pass Temperature is specified as Maximum Temperature allowed in the base metal and weld metal before commencement of next weld pass. Propane gas torch induction heating and electrical resistance heating. Generally speaking preheating helps ensure that the weld has the mechanical properties it was designed to achieve.
The temperature at which the base metal is heated is called as the preheat temperature.
One may also ask when should you preheat metal before welding. The best thing to do is to determine the adequate preheat temperature for the base metal you are welding. Preheating a wider area minimizes the risk of colder areas in the material sucking away the heat. Generally pre-heat is applied up to 1 hour before the welding to ensure even temperature throughout the welding area.