456A Oxyfuel Welding & Cutting 2 — Questions and Answers
Question 1: What minimum distance must separate oxygen and fuel gas cylinders in storage, unless a fire-resistant barrier is used?
- 1.5 m (5 ft)
- 3 m (10 ft)
- 6 m (20 ft) (Correct answer)
- 9 m (30 ft)
Correct answer: 6 m (20 ft)
Canadian fire codes require oxygen and fuel gas cylinders to be stored at least 6 m (20 ft) apart or separated by a non-combustible barrier at least 1.5 m (5 ft) high to prevent both from being involved in a fire.
Question 2: When cutting mild steel with an oxyfuel torch, what reaction actually performs the cut?
- Melting of the steel by the preheat flames alone
- Rapid oxidation (burning) of the preheated steel by the cutting oxygen stream (Correct answer)
- Mechanical action of the high-pressure oxygen blasting away molten metal
- Plasma arc formation within the oxygen jet
Correct answer: Rapid oxidation (burning) of the preheated steel by the cutting oxygen stream
OFC works by heating the steel to its ignition temperature (~870°C) and then directing pure oxygen to rapidly oxidize (burn) the metal, removing it as iron oxide slag — the metal burns rather than melts.
Question 3: Why cannot aluminum be effectively cut using the standard oxyfuel cutting process?
- Aluminum ignites at too high a temperature for the preheat flames to reach
- Aluminum oxide (Al₂O₃) has a higher melting point than the base metal, blocking the oxidation cut (Correct answer)
- Aluminum reacts explosively with the high-pressure cutting oxygen stream
- Aluminum requires a carburizing flame rather than a cutting oxygen jet
Correct answer: Aluminum oxide (Al₂O₃) has a higher melting point than the base metal, blocking the oxidation cut
Aluminum oxide (Al₂O₃) melts at approximately 2050°C, far above aluminum's melting point of 660°C, so the refractory oxide layer prevents the progressive oxidation required for OFC to work.
Question 4: What is the purpose of flux when performing oxyfuel welding on cast iron or bronze?
- To rapidly cool the weld pool and refine grain structure
- To increase the melting point of the filler rod
- To prevent oxidation and chemically remove oxides from the weld pool (Correct answer)
- To add specific alloying elements to the weld deposit
Correct answer: To prevent oxidation and chemically remove oxides from the weld pool
Flux acts as a chemical cleaning agent, dissolving and floating away oxides from the weld pool surface to prevent oxide inclusions and produce a clean, sound fusion bond.
Question 5: What is 'kerf' in the context of oxyfuel cutting?
- The heat-affected zone on either side of the cut
- The angle of the cutting tip relative to the plate surface
- The width of material removed by the cutting process (Correct answer)
- The travel speed of the cutting torch along the cut line
Correct answer: The width of material removed by the cutting process
Kerf is the slot or groove created by the cutting process — the total width of material consumed and removed from the workpiece during the cut.
Question 6: How should acetylene cylinder valves be opened during oxyfuel setup?
- Fully open using a cylinder wrench, same as oxygen
- No more than 1.5 turns from the closed position (Correct answer)
- Exactly 3 full turns open to ensure adequate flow
- Cracked open only, about a quarter turn, for safety
Correct answer: No more than 1.5 turns from the closed position
Acetylene valves should be opened no more than 1.5 turns so the cylinder can be quickly shut off in an emergency, while oxygen valves are opened fully to prevent leakage past the packing.
Question 7: What does a zero reading on the cylinder pressure gauge indicate when the cylinder valve is fully open?
- The regulator delivery pressure is correctly set to zero for startup
- The cylinder is empty and must be replaced (Correct answer)
- The high-pressure gauge needs recalibration
- The cylinder valve is opening in the wrong direction
Correct answer: The cylinder is empty and must be replaced
The high-pressure gauge reads the gas pressure remaining inside the cylinder; a zero reading with the valve open means no gas remains and the cylinder is empty.
456A Oxyfuel Welding & Cutting 2
What minimum distance must separate oxygen and fuel gas cylinders in storage, unless a fire-resistant barrier is used?