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Flame used for most oxy-acetylene welding

Aviation Mechanic Airframe (AMA) practice question 1 of 20 on Metallic Structures. ACS element AM.II.A.K11 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONWhich oxy-acetylene flame is used for most welding because it does not alter the composition of the base metal?

  1. AThe neutral flame
  2. BThe oxidizing flame
  3. CThe carburizing flame
Show the answer and explanation

Correct answer: A. The neutral flame

  • A — correct Produced by a balanced mixture of acetylene and oxygen, it is used for most welding precisely because it does not alter the composition of the base metal.
  • B — incorrect Burning an excess of oxygen makes molten steel foam, spark, and burn; this flame is reserved for bronze welding and for fusion welding of brass and bronze.
  • C — incorrect Burning more acetylene than oxygen adds carbon to the metal, which suits high-carbon steels, hard facing, and certain nonferrous alloys instead of general work.

BACKGROUND

Three oxy-acetylene flames are in common use, and each is recognized by sight and sound as well as by its mixture. The neutral flame burns at about 5,850 degrees Fahrenheit at the tip of the inner luminous cone and comes from a balanced mixture of acetylene and oxygen; on steel it leaves the molten puddle quiet and clear so the metal fuses without burning or sparking. The carburizing or reducing flame burns at about 5,700 degrees Fahrenheit, is recognized by a greenish feathery tip, and suits high-carbon steels, hard facing, and nonferrous alloys such as aluminum, nickel, and Monel. The oxidizing flame burns at about 6,300 degrees Fahrenheit with a short outer flame, a small pointed inner cone, and a hissing sound. Because the neutral flame leaves the base metal chemically unchanged, it is the one used for most welding.

STUDY TIP

Anchor each flame to its recognition cue and its intended metal: neutral for most work, feathered carburizing for high-carbon and nonferrous, hissing oxidizing for brass and bronze.

KEY POINTS

  • The neutral flame comes from a balanced oxygen and acetylene mixture and does not alter the base metal.
  • Carburizing flame has a greenish feather and suits high-carbon steels and nonferrous alloys.
  • An oxidizing flame on steel makes the puddle foam, spark, and burn.

SOURCES

  • sources/ama-airframe/ch05.txt "Different Flames — Neutral Flame"
  • sources/ama-airframe/ch05.txt "Carburizing Flame"
  • sources/ama-airframe/ch05.txt "Oxidizing Flame"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.