Pre-Heat
Preheating of the base material minimizes the temperature difference between the material and the arc, slows the cooling rate in the weld area and reduces the risk of cracking.
The preheat necessity increases with steel thickness, weld restraint, the carbon/alloy content of the steel, and the diffusible hydrogen of the weld metal. Preheat is commonly applied with fuel gas torches or electrical resistance heaters. Although the process can seem expensive, it can save time and costs in the long term by reducing risk of failed weld.
The purpose of preheat:
- Reduce the risk of hydrogen cracking
- Reduce the hardness of the heat affected zone
- Reduce shrinkage stresses during cooling and improve the distribution of residual stresses.