Oxy–acetylene welding — condition for a neutral flame In gas welding, which gas flow condition produces a neutral flame (chemically balanced flame with neither oxidizing nor carburizing tendency)?

Introduction / Context:
Flame chemistry in oxy–acetylene welding directly affects weld pool metallurgy and surface appearance. A neutral flame is the default choice for steels and many nonferrous alloys because it neither adds excess carbon nor strips alloying elements by oxidation.

Given Data / Assumptions:

• Gases: oxygen (O2) and acetylene (C2H2) with standard welding tips.
• Neutral flame desired for balanced chemistry.
• Operator adjusts flows to observe inner cone length and feather.

Concept / Approach:
A neutral flame forms when oxygen and acetylene are supplied in roughly equal volumetric proportions at the tip, resulting in complete combustion: C2H2 + O2 (primary) followed by secondary combustion with surrounding oxygen. The visual cue is a well-defined inner cone with no acetylene feather. An oxidizing flame uses excess oxygen (short, sharp inner cone, hissing sound), while a carburizing (reducing) flame uses excess acetylene (long feather beyond inner cone) and can introduce carbon or soot into the weld.

Step-by-Step Solution:

Verification / Alternative check:
Welding handbooks define neutral flame at approximately 1:1 oxygen-to-acetylene ratio by volume at the tip, with allowances for tip size and back pressure.

Why Other Options Are Wrong:

• Excess oxygen: oxidizing flame, risks porosity and oxide inclusions.
• Excess acetylene: carburizing flame, risks soot and carbon pick-up.
• “None of the above” or oxygen off: do not produce a neutral welding flame.

Common Pitfalls:
Judging solely by sound; ignoring the acetylene feather; not compensating for tip size and regulator settings.

Final Answer: