456A Oxyfuel Welding & Cutting 1 — Questions and Answers
Question 1: What type of flame is produced when oxygen and acetylene are mixed in equal proportions?
- Carburizing flame
- Neutral flame (Correct answer)
- Oxidizing flame
- Reducing flame
Correct answer: Neutral flame
A neutral flame results from an equal mixture of oxygen and acetylene, producing a well-defined inner cone with no acetylene feather, making it ideal for welding most steels.
Question 2: What is the maximum allowable working pressure for acetylene in Canada?
- 35 kPa (5 psi)
- 70 kPa (10 psi)
- 103 kPa (15 psi) (Correct answer)
- 207 kPa (30 psi)
Correct answer: 103 kPa (15 psi)
Acetylene becomes chemically unstable and risk of explosive decomposition above 103 kPa (15 psi), making this the absolute maximum safe working pressure.
Question 3: In Canada, what color is the oxygen hose used in oxyfuel equipment?
- Red
- Black
- Blue
- Green (Correct answer)
Correct answer: Green
In Canada, the oxygen hose is green with right-hand threaded fittings to clearly distinguish it from the red fuel gas hose and prevent dangerous cross-connection.
Question 4: What is the primary purpose of a flashback arrestor in an oxyfuel system?
- To regulate gas pressure at the torch
- To prevent flame from traveling back into the hoses and cylinders (Correct answer)
- To mix oxygen and fuel gas in the correct ratio
- To filter impurities from the gas supply
Correct answer: To prevent flame from traveling back into the hoses and cylinders
Flashback arrestors contain a flame barrier and check valve that stop a backfiring flame from propagating back through the hoses toward the cylinders, preventing a catastrophic explosion.
Question 5: Which type of oxyfuel flame is characterized by an acetylene feather between the inner cone and outer envelope, and is used for welding high-carbon steel?
- Neutral flame
- Oxidizing flame
- Carburizing (reducing) flame (Correct answer)
- Balanced flame
Correct answer: Carburizing (reducing) flame
A carburizing flame has excess acetylene, producing a luminous feather that adds carbon to the weld pool — useful for hard-facing and high-carbon steel applications.
Question 6: When lighting an oxyfuel torch, which gas valve should be opened and ignited first?
- Oxygen
- Both simultaneously
- Either gas can be opened first
- Acetylene (fuel gas) (Correct answer)
Correct answer: Acetylene (fuel gas)
Fuel gas (acetylene) is always opened and lit first to establish a flame before oxygen is added, preventing the risk of creating an explosive pre-mixed atmosphere in the air.
Question 7: What distinguishes an oxyfuel cutting tip from a standard welding tip?
- Cutting tips have a single large orifice only
- Cutting tips are made of stainless steel
- Cutting tips have a central cutting oxygen orifice surrounded by preheat holes (Correct answer)
- Cutting tips operate at higher acetylene pressure than welding tips
Correct answer: Cutting tips have a central cutting oxygen orifice surrounded by preheat holes
A cutting tip has a central high-pressure oxygen jet orifice for the cutting stream, surrounded by smaller preheat flame holes that raise the metal to its ignition temperature before cutting begins.
456A Oxyfuel Welding & Cutting 1
What type of flame is produced when oxygen and acetylene are mixed in equal proportions?