Question

One of the crack-prevention measures in welding is to preheat the components to be welded. Describe the rea For the toolbar, press ALT+F10 (P) Of ALT FN+F10 (Mac). 25

Answer 1

Preheating the steel to be welded slows the cooling rate in the weld area. This may be necessary to avoid cracking of the weld metal or heat affected zone.

The need for preheat 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.

The purpose of preheat:

1. Reduce the risk of hydrogen cracking
2. Reduce the hardness of the weld heat affected zone
3. Reduce shrinkage stresses during cooling and improve the distribution of residual stresses.

If preheat is locally applied it must extend to at least 75mm from the weld location and be preferably measured on the opposite face to the one being welded.