Preheating before Welding

March 27, 2021 0 By sajle

To reduce the risk of cracking in weld metal and heat-affected zone (HAZ), heating before actual welding is carried out. The level and need for preheat is determined by the applicable welding code and is dependent on the following:

  • Heat input during welding
  • Carbon equivalent derived from the chemical composition of steel
  • Thicknesses of the materials being welded
  • Diffusible hydrogen

Preheating results in the following:

  • Prevents formation of brittle weld metal/HAZ and allows more time for hydrogen to escape the molten weld by lowering the cooling rate of the weld.
  • Reduces shrinkage by lowering the temperature differential between weld metal/HAZ and the surrounding metal.
  • Removes hydrogen source from the part by removing moisture.