In oxyfuel welding, which flame type is the hottest?

• A. Carburizing flame
• B. Neutral flame
• C. All flames are equally hot
• D. Oxidizing flame

Answer: (D)

In oxyfuel welding, flame temperature rises with more oxygen in the mix. The oxidizing flame has excess oxygen, which drives the combustion to a higher adiabatic temperature, making it the hottest. The neutral flame is stoichiometric—balanced between fuel and oxygen—so it’s hot but not as hot as the oxidizing flame. The carburizing flame is fuel-rich and tends to produce carbon and incomplete combustion, which cools the flame and reduces heat transfer efficiency. So, the hottest is the oxidizing flame.