When using an acetylene cutting torch, how should the flame appear?

When using an acetylene cutting torch, how should the flame appear?

• A. Shorter than 2 inches, blue and white
• B. Longer than 6 inches, yellow
• C. About 4 inches, orange
• D. Shorter than 2 inches, red and yellow

Answer: (D)

In oxy-fuel cutting, the preheat flame should be a carburizing (fuel-rich) flame that is kept short to precisely heat the metal to its ignition temperature. The smoky red and yellow appearance shows that there is excess acetylene, which helps bring the steel to the right heat quickly without flooding it with an oxidizing environment. Keeping the flame shorter than about 2 inches concentrates the heat where you want it and reduces the risk of overheating surrounding area or causing distortion. Other flame colors and lengths indicate different mixtures or heat zones not suitable for preheating in cutting. A blue/white neutral flame or an elongated flame would not provide the proper heat characteristics for ignition, and a long, orange flame suggests too much heat spread or an overly fuel-rich condition that’s harder to control.

In oxy-fuel cutting, the preheat flame should be a carburizing (fuel-rich) flame that is kept short to precisely heat the metal to its ignition temperature. The smoky red and yellow appearance shows that there is excess acetylene, which helps bring the steel to the right heat quickly without flooding it with an oxidizing environment. Keeping the flame shorter than about 2 inches concentrates the heat where you want it and reduces the risk of overheating surrounding area or causing distortion.

Other flame colors and lengths indicate different mixtures or heat zones not suitable for preheating in cutting. A blue/white neutral flame or an elongated flame would not provide the proper heat characteristics for ignition, and a long, orange flame suggests too much heat spread or an overly fuel-rich condition that’s harder to control.