OXY-FUEL CUTTING (OFC) · FLAME CUTTING
Oxy-fuel cutting heats steel to ignition temperature with preheat flames and then oxidizes the steel with a high-velocity cutting oxygen jet. The oxidation reaction sustains heat and the gas momentum ejects slag through the kerf. This is a cutting process — distinct from gas welding — with its own torch, tips, and operating principles.
PREHEAT · OXYGEN JET · KERF
Cutting Process — not Welding Process
Oxy-fuel cutting (OFC), also called flame cutting, separates steel by rapid oxidation rather than by melting alone. Preheat flames bring the surface to a kindling temperature where iron will burn in oxygen. When the cutting oxygen lever is opened, a central high-velocity oxygen stream oxidizes the heated steel through the thickness and blows the molten iron oxide and slag out of the cut. Travel advances the reaction along the cut line.
It is related to gas welding by the shared oxygen and fuel-gas supply family, but the mechanism, torch configuration, consumable tip, and resulting joint (a removed kerf rather than a fused weld pool) are different. Oxy-fuel cutting is classified here as a Cutting Process and appears under Cutting, not under Welding Processes.
Preheat flames
Oxygen jet
Kerf + slag ejection
Tip orifice, gas delivery, preheat condition, travel speed, and plate thickness jointly determine cut behavior. Use the manufacturer tip chart for equipment-specific values — there are no universal pressure or tip-size settings.
The three cutting stages occur in sequence at the cut front: preheating brings the steel to ignition, the oxygen jet oxidizes through the thickness, and the ejected slag clears the kerf for advance. The diagram below labels preheat, cutting-oxygen jet, kerf, and slag ejection.
Peripheral flames heat a spot or line to ignition temperature. The surface turns bright before the oxygen jet is effective. Insufficient preheat delays or stalls initiation.
The lever releases the central oxygen jet onto the heated zone. Iron oxidizes rapidly, generating additional heat that sustains heating of the next material layer.
Jet momentum ejects molten oxide and slag through the kerf to the underside. Complete ejection clears the path so travel can advance; incomplete ejection leaves adherent dross.
A cutting torch blends fuel gas and oxygen for the preheat flames and controls them with separate valves. The central cutting-oxygen passage terminates in the tip orifice. Tips are consumables sized by orifice and preheat configuration; tip selection directly affects kerf width, achievable thickness, and cut quality. Use only tips compatible with the torch model and gas service.
Oxygen has two roles: it supports combustion of the fuel gas in the preheat flames and, as the cutting jet, it oxidizes the base steel. Fuel gas (acetylene, propane, propylene, or natural gas) fuels only the preheat. Fuel choice affects preheat characteristics and pierce behavior but does not replace the oxygen jet's oxidation function.
OXYGEN
Preheat oxidizer + cutting oxidizer and ejection momentum. Purity and delivery stability matter.
FUEL GAS
Preheat energy only. Acetylene has distinct flame and handling requirements. Confirm configuration per manufacturer.
A neutral or near-neutral setting provides stable, even heating. Excess carburizing or oxidizing character can disturb preheat uniformity. Adjust for the material condition rather than assuming one setting.
A coherent, centered jet penetrates the full thickness and ejects slag below the plate. Jet coherence depends on orifice condition, standoff, and delivery stability across the thickness.
Hold the tip slightly above the surface at ignition, preheat until the spot is uniformly bright, then open the oxygen lever smoothly while maintaining position until the jet punches through. Advance only after the pierce is confirmed on the underside.
Tip-orifice size, oxygen flow capacity, and plate thickness are linked: thicker material generally requires a larger orifice and greater oxygen mass flow to sustain oxidation and ejection through the thickness, while thinner material benefits from a smaller orifice and faster travel to limit heat input and kerf widening. No single pressure, tip size, or thickness limit applies universally. Use the applicable manufacturer tip chart and qualified procedure to map thickness to recommended tip, flow, and standoff — and observe the trend, not a fixed number.
There are no universal pressures, tip sizes, gas-flow values, or thickness limits. The relationships below describe direction and interaction; equipment-specific values must come from the tip chart and procedure.
Regulator setting, hose condition, and oxygen purity affect jet coherence and thickness capability. Leaks or pressure droop degrade the jet.
Preheat intensity and duration bring the entry point to ignition. Too little preheat stalls the start; excess preheat broadens the heat-affected zone.
Travel speed, torch angle, and standoff determine heat input per unit length, kerf straightness, and whether oxidation keeps pace with advance.
Tip orifice, orifice condition, and preheat-orifice arrangement constrain attainable speed and quality for a given thickness.
| Change | Effect | Verification |
|---|---|---|
| Larger tip orifice (within chart range) | More oxygen mass flow → higher penetration capability, wider kerf | Check chart for matching thickness and flow; inspect kerf width |
| Faster travel | Less heat per unit length → tighter kerf, may leave incomplete penetration or heavier drag if too fast | Observe drag lines and underside slag ejection |
| Slower travel | More heat per length → rounded top edge, wider kerf, molten buildup below plate | Inspect top-edge rounding and dross adhesion |
| Increased standoff | Jet disperses → less penetration, angled kerf walls, more spatter | Measure kerf perpendicularity, check slag position |
| Low oxygen flow vs. chart | Incomplete oxidation/piercing, persistent slag adherence | Restore supply, recheck regulator and tip condition |
Do not treat these as setpoints. They describe trends to diagnose while confirming values against the correct chart.
The kerf is the slot removed by the cut. Its width is set primarily by the cutting orifice and operating condition. Plate thickness, speed, and standoff shift it measurably. Consistent kerf width enables dimensional planning and nesting.
Vertical striations on the cut face. When nearly vertical, speed and jet coherence are reasonably matched. Heavy rearward drag (lines leaning sharply behind the direction of travel) suggests excessive speed or an attenuated jet; over-penetration with melted upper edge suggests too slow.
Solidified slag on the underside. Low-speed dross is globular and on the bottom edge, easily knocked off. High-speed dross is a tight, stringy bead along the lower kerf wall that indicates the jet was outrun and had insufficient time to oxidize through.
Gouged / irregular kerf: Unstable preheat, worn orifice, or contaminated oxygen path.
Excessive top-edge melting: Too slow, excessive preheat, or incorrect tip.
Bevel or angled kerf walls: Torch not perpendicular, incorrect standoff, or tip damage.
Incomplete cut / hang-up: Insufficient oxygen flow, too fast, or thickness beyond chart capability.
Tear / ragged bottom edge: Contamination, poor pierce initiation, or travel hesitation.
Most cutting is perpendicular. A slight lead can help initial penetration on thicker starts; sustained lean degrades kerf perpendicularity.
Starting off the plate edge avoids a pierce and reduces molten blowback. Use piercing only where geometry requires it.
Close cutting oxygen before extinguishing preheat to avoid oxidizing the cut termination unevenly. Maintain position momentarily to clear the kerf.
Plain carbon steel and many low-alloy steels oxidize readily and cut well with oxy-fuel. Plate thickness capability is tip- and supply-dependent; the correct chart maps the combination to the achievable range. Kerf width and gas demand rise with thickness, and travel speed naturally falls.
Stainless steels (chromium oxide barrier), cast irons, aluminum, copper, and copper alloys do not sustain the iron-oxidation reaction and are not effectively cut by oxy-fuel. Use plasma, laser, or mechanical cutting for these materials.
Thicker plate retains more heat but demands more oxygen mass flow to oxidize through and eject slag. Thin sheet is more sensitive to overheating and top-edge rounding — faster travel and smaller tips reduce dwell. Always treat thickness capability as a combination of tip, gas, and procedure, not as a universal limit printed on this page.
Follow manufacturer instructions, site hot-work procedure, and governing regulations. Do not invent pressures, storage distances, or shutdown sequences.
Secure upright, identify by label, use compatible regulators. Oxygen and fuel systems remain separate until the torch.
Keep oxygen equipment free of oil and grease. Oxygen-enriched atmospheres greatly increase fire risk.
Remove combustibles, cover openings, stage fire watch where required, and consider slag trajectories that extend meters below the kerf.
Check valves and flashback arrestors have distinct roles. Repeated backfires or any flashback require immediate stop and inspection per manufacturer/site procedure.
Use correct shade for oxy-fuel cutting, gloves, flame-resistant clothing, and ventilation appropriate to the material and environment.
Inspect hoses, connections, and fittings; use approved leak-detection methods. Suspected leak means stop and follow site procedure.
Ejected molten oxide can ignite surroundings and burn through footwear or clothing. Clear the zone below and beyond the cut.
Sequence equipment shutdown per manufacturer instructions. Do not improvise the order of closing cutting oxygen, fuel, and oxygen valves.
Principle of material removal and gas roles determine the right cutting method for a given thickness, material, quality, and productivity need.
| Factor | Oxy-Fuel Cutting | Plasma Cutting | Laser Cutting |
|---|---|---|---|
| Heat / removal | Chemical oxidation by cutting oxygen | Constricted arc + ionized gas melting and ejection | Focused light energy + assist gas ejection |
| Shielding / gas | Preheat fuel + cutting oxygen | Plasma and shielding gases | Assist gas (O₂/N₂/air) depending on mode |
| Materials | Strong on carbon/low-alloy steel | Broader: steels, stainless, aluminum | Broader with reflective-material considerations |
| Thickness + speed | Competitive on thick steel, slower on thin | Fast on thin and medium, pierces well | Fast on thin and medium, very precise cut face |
| Edge quality driver | Kerf, drag, dross controlled by tip/jet/speed | Consumable, current, gas, standoff | Focus, power, assist gas, speed |
| Typical choice driver | Thick plate, field portability, lower capital cost | Versatility, pierce-heavy work, speed on non-ferrous | Precision, fine features, tight tolerances, automation |
Plate preparation, bevels, removal of excess, and field trimming where portability and thick-section capability matter.
Sectioning structural steel and scrap where edge finish is secondary to separation capability.
Opening access, removing cracked or worn sections, and preparing joints for subsequent welding.
Where material does not oxidize effectively, where fine-feature tolerance or minimal heat input is required, or where speed on thin non-ferrous work governs, consider plasma or laser methods.
It is a cutting process that heats steel to ignition with preheat flames and then oxidizes it through the thickness with a high-velocity cutting oxygen jet, ejecting the molten oxide as slag through the kerf.
Preheat heats the steel to kindling temperature. The central cutting oxygen jet oxidizes the heated steel and provides the momentum to eject molten material from the kerf. Both are required.
The width of material removed during the cut. It is set primarily by the cutting tip orifice and operating condition; use the manufacturer tip chart to relate tip size to expected kerf and thickness.
Acetylene, propane, propylene, and natural gas can all serve as fuel gases for cutting in the appropriate torch and tip configuration. Follow manufacturer and procedure guidance for the selected fuel.
It effectively cuts carbon and low-alloy steels. Stainless steels, cast irons, aluminum, and copper alloys are not effectively cut by oxy-fuel oxidation and require a different cutting process.
Oxy-fuel removes material by oxidation with oxygen. Plasma uses a constricted arc to melt and blow away metal. Laser uses focused light energy with assist gas. Each principle leads to different speed, edge quality, and applicable materials.
Discuss a cutting torch, tip chart, and gas configuration for your material thickness and site.
When oxidation cutting is not effective, plasma equipment provides broader material capability.
High precision and fine features driven by focused light energy and assist gas.
Related oxy-fuel welding process using the same gas family with a fusion-welding mechanism. Cross-link, not a synonym.
Broad and localized heating with controlled temperature for preheat and forming.
Shallow-angle oxidation forming a controlled groove for defect removal and back-gouging.