Welding Preheat Is Important to Ensure Weld Quality
Pre-Weld Heat Treatment or Preheating in welding is used to help ensure weld quality and reduce the occurrence of cracking and other problems that can result in costly rework.
Welding preheat is commonly used before welding steel or steel alloy pipes or plates that are 1 inch thick or more. Preheating is often required in shop and field welding for oil and gas, transmission pipelines, power plants, structural construction, mining, shipbuilding and heavy equipment applications.
PURPOSE OF PREHEAT
The process of preheating involves heating the area around the weld joint or the entire part to a specified temperature before welding. This reduces the cooling rate of the weld and drives out moisture, which in turn helps prevent hydrogen buildup and the potential for cracking.
- Reduce the risk of hydrogen cracking
- Reduce the hardness of the weld heat affected zone
- Reduce shrinkage stresses during cooling
- Improve the distribution of residual stresses.
Preheat can be applied through various means. The choice of method of applying preheat will depend on the material thickness, weldment size and the heating equipment available at the time of welding. The methods can include furnace heating for small production assemblies or, for large structural components, arrays of torches, electrical strip heaters, induction heaters or radiation heaters.
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