Preheating & Other Metallurgy of Welding

Front

Why do we preheat in welding?

Back

To slow the cooling rate in the weld metal and base metal, producing a more ductile structure with resistance to cracking.

Front

What does slow cooling rate during preheating allow?

Back

It allows hydrogen to diffuse out harmlessly, reducing the potential for hydrogen-induced cracks.

Front

How does preheating affect shrinkage stresses?

Back

It reduces shrinkage stresses in the weld and adjacent base metal.

Front

What is the fourth reason for preheating?

Back

It raises some steel's temperature above the brittle fracture temperature during fabrication.

Front

What factors should be considered when determining whether to preheat?

Back

Code requirements, base metal thickness and chemistry, restraint of sections, ambient temperature, and type of welding consumable.

Front

How can preheat temperature be determined?

Back

Using a material test report and a preheat/interpass temperature calculator.

Front

What tools are typically used to measure preheat temperatures?

Back

Temperature sticks or digital pyrometers.

Front

What is a safe preheat temperature for home welding?

Back

Around 400-500 degrees Fahrenheit to slow cooling.

Front

How far should preheating extend around the material?

Back

Minimum three inches in all directions from the thickness of the material.