Preheating Before Welding: Techniques and Parameters for Optimal Results

Before the start of the formal welding work, the weld joint area of the thick steel plate should be preheated.

During welding, cracks may occur in the welding area due to local rapid heating and cooling.

Preheating is a process to slow down the rapid heating and cooling process in the welding area.

Joints with high restraint force can reduce shrinkage stress after preheating, and preheating can also eliminate moisture and humidity in the welding area, eliminating the source of hydrogen gas.

When welding, the appropriate preheating temperature should be selected according to the ambient temperature of the work site, the material and thickness of the steel, and preheat the weldment.

When there are no special requirements, the preheating temperature can be selected according to Table 1.

Table 1 Commonly used preheating temperature.

Steel classificationambient temperaturePlate thickness (mm)Preheating and interlayer temperature control (℃)
Ordinary carbon structural steelAbove 0 ℃≥5070~100
Low alloy structural steelAbove 0 ℃≥3670~100

For components that require preheating, preheating should be carried out evenly within a 100mm range on both sides of the weld line before welding. The measurement of the preheating temperature should be taken 50mm away from the weld line.

Table 2 Conditions for preheating required for different thickness of steel materials.

Low carbon steel componentsLow carbon steel pipe componentsQ345,16Mnq 15MnV, 15MnVg components
Steel thickness
(mm)
Temperature below
(℃)
Steel pipe wall thickness
(mm)
Temperature below
(℃)
Steel thickness
(mm)
Temperature below
(℃)
≤30-30≤16-30≤10-26
31~50-1017~30-2010~1610
0   16~24-5
51~70031~40-1025~400
  41~500Above 40Any temperature

When the ambient temperature at the work site is below 0℃, the preheating temperature of the welding component should be determined by trial.

Table 3 Preheating temperature required for different material steel materials.

Carbon content in carbon steel
(%)
Preheating temperature
(℃)
low alloy steelPreheating temperature
(℃)
<0.20Not preheating  
0.20~0.30<100  
Carbon content in carbon steel
(%)
Preheating temperature
(℃)
low alloy steelPreheating temperature
(℃)
0.30~0.45100~200 100~150
0.45~0.80200~400  

When welding in an environment where the temperature is below 0℃, low carbon steel should also be preheated.

Table 2 is the condition for preheating thick steel plate. Table 3 is the temperature that needs to be preheated.

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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