20 Thermal Cutting Processes Practice Questions & Answers
Every Thermal Cutting Processes practice question from the Welding Practice Test, with the correct answer and a short explanation.
Start practice test →1. A shop must cut a 1/2 in. aluminum plate. Why will an oxyfuel cutting torch not produce a clean cut in it?
- A.Its thermal conductivity carries the preheat away so fast that the plate never reaches red heat
- B.Its oxide melts far above the metal's own melting point, so the plate simply melts instead of burning away✓ Answer
- C.It burns so readily in the oxygen jet that the kerf widens out of control instead of staying narrow
- D.Its melting point is higher than any temperature an oxyacetylene preheat flame can produce
Oxyfuel cutting is a chemical process: the cutting oxygen burns the hot iron and the jet flushes the liquid oxide out of the kerf. It only works when the oxide melts below the base metal. Aluminum oxide melts far above molten aluminum, so it forms a refractory skin the jet cannot clear, which is why aluminum and austenitic stainless steel are cut with plasma instead.
Source: AWS EG2.0, Guide for the Training of Welding Personnel: Level I, Entry Welder (oxyfuel cutting limited to metals whose oxide melts below the base metal)Report a problem with this question
2. In manual oxyfuel cutting of carbon steel, what must happen at the start point before the cutting-oxygen lever is pressed?
- A.It must be heated until the surface turns blue, showing the mill scale has been burned off
- B.It must be heated to a dull red, at which the steel is soft enough to be blown out of the kerf
- C.It must reach a bright cherry red, the kindling temperature, which lies below the melting point✓ Answer
- D.It must be brought just to the melting point so the oxygen jet can flush the molten pool out
Oxygen cutting burns steel rather than melting it. The preheat flames only raise the metal to its kindling (ignition) temperature, a bright cherry red that is well below the melting point; the cutting oxygen then oxidizes the iron and the reaction's own heat sustains the cut as the jet blows the slag out.
Source: AWS A3.0, Standard Welding Terms and Definitions (oxygen cutting: severing by the chemical reaction of oxygen with the base metal at elevated temperature)Report a problem with this question
3. A welder sets the cutting torch preheat flames to neutral, then presses the cutting-oxygen lever and an acetylene feather appears. What is the correct response?
- A.Leave it as set, since a feather under cutting oxygen shows the tip size matches the plate thickness
- B.Readjust the preheat flames back to neutral with the cutting-oxygen lever held down, then release it✓ Answer
- C.Raise the fuel-gas working pressure at the regulator until the feather disappears with the lever down
- D.Close the cutting-oxygen valve on the torch slightly until the flames return to neutral on their own
Opening the cutting oxygen draws down the oxygen available to the preheat orifices, so flames set neutral with the lever released usually go carburizing when it is pressed. The preheat must be neutral while cutting, so the flames are readjusted with the lever held down; a carburizing preheat adds carbon to the cut face and a feather means unburned fuel.
Source: AWS EG2.0, Guide for the Training of Welding Personnel: Level I, Entry Welder (neutral preheat flame adjustment for oxyfuel cutting)Report a problem with this question
4. How is a carburizing oxyacetylene flame recognized, and what does it do to the steel?
- A.The inner cone is short and necked in, and the excess fuel scales the surface of the steel heavily
- B.The flame is long, blue and quiet, and the excess fuel cools the steel below its kindling point
- C.A feather trails off the inner cone, and the excess fuel adds carbon to the surface of the steel✓ Answer
- D.No feather shows at all, and the excess fuel leaves the cut face soft and easy to bend afterward
A carburizing flame has more fuel than the oxygen can burn, so unburned acetylene shows as a feather around the inner cone. The surplus carbon is absorbed by hot steel, hardening and embrittling the surface, which is why the preheat for cutting is set neutral rather than carburizing.
Source: AWS A3.0, Standard Welding Terms and Definitions (carburizing flame: an oxyfuel gas flame with an excess of fuel gas)Report a problem with this question
5. A cutting torch gives a shrill squeal and the flame disappears back inside the torch. What is happening, and what does the operator do first?
- A.A flashback; shut the fuel valve first so the gas burning inside the torch is starved of fuel
- B.A backfire; raise both working pressures to push the flame back out to the face of the tip
- C.A backfire; relight the tip at once and keep cutting, since the flame will settle down by itself
- D.A flashback; shut the torch oxygen valve first, then the fuel valve, and let the torch cool✓ Answer
A shrill squeal with the flame burning inside the torch is a flashback, not a backfire (a backfire is a loud pop where the flame goes out or relights at the tip). Oxygen is what sustains that internal flame, so the oxygen valve is closed first, then the fuel, and the equipment is inspected before it is used again.
Source: ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes (response to flashback in oxyfuel gas equipment)Report a problem with this question
6. What is the difference between a reverse-flow check valve and a flashback arrestor on an oxyfuel outfit?
- A.A check valve vents excess pressure to the air; an arrestor blocks flow between the two hoses
- B.A check valve stops backflow and flame both; an arrestor only limits working pressure in the hose
- C.A check valve quenches a flame in the hose; an arrestor keeps fuel gas out of the oxygen regulator
- D.A check valve only stops gas from flowing backward; an arrestor also quenches a flame inside the hose✓ Answer
A reverse-flow check valve is a one-way valve: it keeps oxygen and fuel from mixing by flowing back up the wrong hose, but a flame front travels far faster than the valve can seat, so it will not stop a flashback. A flashback arrestor contains a flame-quenching element and shuts off flow, which is why the two devices are not interchangeable.
Source: ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes (reverse-flow check valves and flashback arrestors)Report a problem with this question
7. Why must an acetylene cylinder be used and stored with the valve end up?
- A.Lying it down puts the fusible safety plug above the gas, so it can no longer relieve pressure
- B.Lying it down lets the porous filler shift, so the cylinder valve can no longer be closed fully
- C.Lying it down lets the gas fall below its dew point, so water collects and freezes in the hose
- D.Lying it down lets liquid acetone be drawn out with the gas, harming the torch and the flame✓ Answer
Acetylene is unstable as a free gas, so the cylinder is packed with a porous filler saturated with acetone in which the gas is dissolved. Standing the cylinder valve-end-up keeps the liquid acetone below the gas space; on its side, acetone is carried into the hose and torch, spoiling the flame and damaging the equipment.
Source: ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes (acetylene cylinders stored and used valve end up)Report a problem with this question
8. An oxyfuel cut face shows drag lines trailing sharply backward and the bottom of the plate is not severed in places. What caused it?
- A.Travel speed too fast for the thickness, so the cutting reaction lags behind the tip✓ Answer
- B.Travel speed too slow, so the reaction runs ahead of the tip and undercuts the bottom edge
- C.Preheat flames set too rich, so carbon builds up and closes the kerf behind the cut
- D.Cutting oxygen pressure too high, so the jet blows the reaction sideways out of the kerf
Drag is the horizontal offset between where the cut enters the top and leaves the bottom, and drag lines record it. At the correct speed they run nearly vertical; when travel outruns the oxidation reaction they lag sharply backward and the reaction may never reach the bottom, leaving the plate uncut and heavy dross attached.
Source: AWS C4.1, Criteria for Describing Oxygen-Cut Surfaces (drag lines as the indicator of travel speed)Report a problem with this question
9. What is the correct way to pierce a hole in the middle of a carbon steel plate with a hand cutting torch?
- A.Preheat to red, then drag the tip in from the edge so the kerf runs out to the marked hole location
- B.Preheat to red, hold the tip flat against the plate surface, and snap the cutting oxygen fully open
- C.Preheat to red, then raise and tilt the tip so the first blowback misses it, and open the oxygen slowly✓ Answer
- D.Skip the preheat and open the cutting oxygen fully, letting the jet drill through the cold plate
When the oxygen first breaks through, molten slag blows straight back up out of the puddle. Raising and tilting the tip throws that blowback clear so it cannot plug the preheat orifices or damage the tip, and opening the oxygen slowly lets the hole open progressively before the torch is levelled and the cut is carried on.
Source: AWS EG2.0, Guide for the Training of Welding Personnel: Level I, Entry Welder (piercing with the manual oxyfuel cutting torch)Report a problem with this question
10. Why is a straight cut made with a motor-driven track burner normally held to a higher quality standard than the same cut made by hand?
- A.The carriage burns a hotter gas mixture, so the kerf face is remelted after the flame has passed
- B.The carriage holds a constant speed and standoff, so drag lines stay uniform and the edge square✓ Answer
- C.The carriage uses far more cutting oxygen, which burns the walls of the kerf smoother than by hand
- D.The carriage needs no preheat, so the plate stays cool and the cut face cannot roughen or distort
AWS C4.1 lists operator ability and the condition of the torch or cutting machine among the variables that govern cut quality. A track burner removes the hand tremor and speed variation of manual work, so travel speed and tip height stay constant and the resulting drag lines are more uniform and the face squarer.
Source: AWS C4.1, Criteria for Describing Oxygen-Cut Surfaces (variables affecting cut quality, including operator ability and machine condition)Report a problem with this question
11. A job calls for cutting an irregular curved outline in carbon steel plate. Why is a hand torch chosen over the track burner?
- A.The carriage cannot reach the travel speed a curve demands, so the cut face would be badly gouged
- B.The carriage follows a straight track only, so a curved contour must be steered by hand✓ Answer
- C.The carriage cannot make a square-edge cut, so any shaped part would come out heavily bevelled
- D.The carriage cannot pierce a start hole, so any cut not starting at a plate edge must be done by hand
Mechanized oxyfuel gains its accuracy from a rigid straight track, which is exactly what limits it: the carriage repeats a straight line or a straight bevel. Shape cutting to a layout line is a manual skill at this level, so an irregular contour is cut freehand with a hand torch guided by the operator.
Source: AWS EG2.0, Guide for the Training of Welding Personnel: Level I, Entry Welder (mechanized oxyfuel straight and bevel cuts; shape cutting performed manually)Report a problem with this question
12. How does plasma arc cutting remove metal from the kerf?
- A.A constricted arc melts the metal and a high-velocity jet of ionized gas blows the melt out✓ Answer
- B.The arc raises the metal to its kindling point and the plasma gas then oxidizes it out of the kerf
- C.The arc vaporizes the metal completely, so no molten metal or dross ever leaves the kerf at all
- D.The plasma gas reduces the metal to a slag that the force of the arc then lifts out of the kerf
Plasma cutting is a melting-and-blowing process, not an oxidation process. The orifice constricts the arc into a narrow, very hot column and the gas passing through it is ionized so it carries current and leaves at high velocity, so any metal that conducts electricity can be cut regardless of how its oxide behaves.
Source: AWS A3.0, Standard Welding Terms and Definitions (plasma arc cutting: melting with a constricted arc and removal of molten metal by a high-velocity jet of ionized gas)Report a problem with this question
13. A fabricator must cut both an austenitic stainless steel sheet and an aluminum plate. Which process fits the job, and why?
- A.Oxyfuel cutting, because a heavier preheat setting burns through the oxide film on either metal
- B.Plasma arc cutting, because it melts and blows out any metal that will conduct an electric current✓ Answer
- C.Air carbon arc cutting, because the air jet clears the oxide that stops oxyfuel from cutting
- D.Oxyfuel cutting, because both of these metals oxidize faster than carbon steel under the jet
Stainless steel and aluminum both grow refractory oxides that melt far above the base metal, so the oxyfuel reaction stalls on them. Plasma does not depend on oxidation at all: it melts a conductive workpiece and blows the melt away, which is why the training standard assigns stainless and aluminum to the plasma unit.
Source: AWS EG2.0, Guide for the Training of Welding Personnel: Level I, Entry Welder (plasma arc cutting performed on carbon steel, austenitic stainless steel and aluminum)Report a problem with this question
14. In manual plasma arc cutting of plate, how is the cutting circuit connected?
- A.Alternating current, so the electrode-positive half cycle cleans the oxide off the plate surface
- B.Direct current, electrode positive, with the arc transferred from the workpiece to the electrode
- C.Direct current, electrode negative, with the arc transferred from the electrode across to the workpiece✓ Answer
- D.Direct current, electrode negative, with the arc held between the electrode and nozzle throughout
Plasma cutting runs direct current straight polarity, electrode negative and work positive, so the workpiece is part of the circuit and the arc transfers to it. A pilot arc struck between electrode and nozzle only starts the process; a non-transferred arc stays inside the torch and is used on nonconductive material, not for cutting plate.
Source: AWS A3.0, Standard Welding Terms and Definitions (transferred arc; plasma arc cutting circuit)Report a problem with this question
15. A plasma torch that has been cutting well begins producing a wide, heavily bevelled kerf with a lot of dross. Which condition explains this?
- A.The standoff was reduced below the drag shield height, so the arc widens as it leaves the plate
- B.The work clamp was moved farther from the cut, so return current bevels one side of the kerf
- C.The pilot arc was left switched on, so it burns the top edge of the kerf wider as travel goes on
- D.The nozzle orifice has worn oval and oversized, so the arc is no longer tightly constricted✓ Answer
The constricting orifice is what makes the plasma jet narrow and fast. As the nozzle erodes, the orifice goes out of round and oversize, the jet loses velocity and focus, and the cut turns wide, bevelled and dross-laden. Nozzle and electrode are wear items and are inspected and replaced as part of routine torch maintenance.
Source: AWS EG2.0, Guide for the Training of Welding Personnel: Level I, Entry Welder (inspection and replacement of plasma torch consumables)Report a problem with this question
16. Plasma cutting is several times faster than oxyfuel on thin plate. What does that mean for ventilation and eye protection?
- A.A lighter filter shade is acceptable, since the constricted arc stays buried down inside the kerf
- B.Both can be relaxed on conductive metals, since less metal is oxidized than in an oxyfuel cut
- C.The same ventilation and arc-rated shading apply, since plasma throws heavy fume and radiation✓ Answer
- D.Lighter ventilation is acceptable on short cuts, since the plasma gas is air rather than a fuel gas
Speed does not reduce the hazard, it concentrates it. A plasma arc vaporizes metal and coatings into a large volume of fume in a short time and emits intense ultraviolet and infrared radiation, so local exhaust or other ventilation and a filter shade rated for an arc process are required whatever the cutting speed.
Source: ANSI Z49.1, Safety in Welding, Cutting, and Allied Processes (ventilation and eye protection for arc cutting processes)Report a problem with this question
17. How does air carbon arc cutting remove metal?
- A.An arc off a carbon electrode oxidizes the metal and the compressed air cools the groove behind
- B.The carbon electrode is consumed into the groove as filler and the air jet washes it out smooth
- C.An arc off a carbon electrode melts the metal and a compressed air jet blows the melt away✓ Answer
- D.The compressed air burns the carbon electrode and the hot gas jet erodes a groove in the metal
Air carbon arc cutting is a metal-removal process. The arc between a copper-coated carbon-graphite electrode and the work melts a pool, and air issuing from the holder at pressure ejects that molten metal before it can freeze, leaving a groove. Nothing is added to the joint, so its jobs are gouging and scarfing rather than joining.
Source: AWS C5.3, Recommended Practices for Air Carbon Arc Gouging and Cutting (process description)Report a problem with this question
18. In air carbon arc gouging, why must the air jet blow from behind the electrode and be turned on before the arc is struck?
- A.So the arc is blown forward onto fresh metal and cuts deeper for a given current setting
- B.So the molten metal is swept clear of the groove before it can freeze back into place✓ Answer
- C.So the carbon electrode is cooled enough to stop it burning back inside the torch head
- D.So the oxide film ahead of the arc is stripped away and the base metal can melt evenly
The air stream is the removal mechanism, so it must reach the pool the instant metal melts. Air holes positioned behind and beneath the electrode direct the stream along it into the arc and throw the melt forward out of the groove; if air comes on late or blows from the wrong side, the metal freezes back in and the groove is rough and irregular.
Source: AWS C5.3, Recommended Practices for Air Carbon Arc Gouging and Cutting (air stream direction and sequence)Report a problem with this question
19. What polarity is used with a copper-coated carbon-graphite electrode for direct current air carbon arc gouging?
- A.Direct current electrode negative, the same straight polarity connection used for plasma cutting
- B.Either polarity serves, because the compressed air rather than the arc does the metal removal
- C.Direct current electrode positive, the reverse polarity connection that these DC electrodes call for✓ Answer
- D.Direct current electrode negative, so that the copper coating lasts longer and the groove runs cool
Copper-coated DC carbon-graphite electrodes are made for direct current electrode positive, which puts the greater heat in the workpiece and gives the stable, smooth-washing arc the process needs. Plasma cutting runs the opposite way, electrode negative, and confusing the two is the most common polarity error in this module.
Source: AWS C5.3, Recommended Practices for Air Carbon Arc Gouging and Cutting (electrode types and polarity)Report a problem with this question
20. A weld root has been back-gouged with air carbon arc. What must be done to the gouged surface before welding, and why?
- A.Preheat the groove instead of grinding, because the heat drives the carbon deposits back out
- B.Grind it back to bright metal, because carbon left on the surface can harden the weld metal✓ Answer
- C.Wire brush off the loose slag only, because the arc burns any carbon left in the groove away
- D.Leave the surface as gouged, because the carbon film shields the hot groove from the atmosphere
The carbon electrode and the rapidly chilled surface can leave a carbon-enriched, hardened layer on the gouged face. Welding over it risks carbon pickup in the deposit, a hard and crack-sensitive weld, and slag or porosity, so the groove is ground to clean bright metal before the joint is welded.
Source: AWS C5.3, Recommended Practices for Air Carbon Arc Gouging and Cutting (surface preparation of gouged grooves before welding)Report a problem with this question
Practice questions based on the AWS SENSE Level I (Entry Welder) written modules, ANSI Z49.1 safety practice, and AWS A2.4 welding symbols. This bank covers the KNOWLEDGE half of entry-level welding only — the workmanship and welder performance qualification tests are hands-on and cannot be practised here, and this is not preparation for the separate, performance-based AWS Certified Welder credential. AWS, SENSE, and NCCER are marks of their respective organizations; this site is not affiliated with or endorsed by them. Work from your program's current materials, and follow the welding procedure and drawings on your own job rather than any number you remember. About AWS SENSE →