Oxy acetylene welding uses a flame produced by burning acetylene gas mixed with oxygen to melt and fuse metal. The process reaches temperatures around 3,500°C (roughly 6,300°F), hot enough to melt steel and several other metals. While it has largely been replaced by arc welding methods like MIG and TIG for heavy industrial work, oxy acetylene welding remains a go-to technique for repair jobs, thin metal work, and applications where portability and precise flame control matter more than speed.
How the Process Works
Oxygen and acetylene flow from separate pressurized cylinders through hoses to a handheld torch, where they mix inside the torch body before igniting at the tip. The welder controls the ratio of the two gases and directs the resulting flame at the joint where two pieces of metal meet. The intense heat melts the edges of the base metal, and the welder often feeds a filler rod into the molten pool to add material and strengthen the joint. As the torch moves along the seam, the molten metal solidifies behind it, creating a continuous weld.
What sets oxy acetylene apart from arc welding is that no electricity is involved. The heat comes entirely from the chemical combustion of the gas mixture, which gives the welder fine control over how much heat reaches the workpiece. That makes it especially useful for thin metal sections where too much heat would burn through the material.
Equipment You Need
A complete oxy acetylene setup includes two gas cylinders, two regulators, twin hoses, a welding torch with interchangeable nozzles, flashback arresters, and personal protective equipment.
- Gas cylinders. Oxygen is stored at pressures as high as 300 bar, while acetylene is dissolved in acetone inside a porous filler material and stored at a much lower pressure, roughly 15 bar. The cylinders are color-coded for quick identification.
- Regulators. Each cylinder gets its own regulator, which steps the high storage pressure down to a usable working pressure for the torch. A regulator has two gauges: one showing how much gas remains in the cylinder and another showing the outlet pressure being delivered to the hose. A pressure-adjusting screw lets you dial in the correct flow rate. It is critical that an oxygen regulator be rated for at least the same pressure as the cylinder it connects to.
- Hoses. Twin hoses carry each gas from its regulator to the torch. Oxygen fittings use right-hand (standard) threads, while acetylene fittings use left-hand threads, a deliberate design choice that prevents you from accidentally connecting the wrong gas to the wrong line.
- Torch and nozzles. The torch mixes the gases and directs the flame. Torches are rated by the thickness of material they can handle, from light-duty models for sheet steel up to about 2mm thick to heavy-duty versions for plate steel over 25mm. Each torch accepts a range of nozzle tips with different bore diameters. Manufacturers publish tip charts that match nozzle size and gas pressures to the thickness of the metal you’re welding.
- Flashback arresters. These safety devices fit into both the oxygen and acetylene lines between the hoses and the regulators. They stop a flame from traveling backward through the hose and reaching the gas supply, which could cause an explosion. OSHA requires flash-back protection on fuel-gas supply systems. Non-return valves can also be fitted in the hoses to detect and stop reverse gas flow.
Three Flame Settings and When to Use Them
The character of the flame changes depending on the oxygen-to-acetylene ratio, and choosing the right setting is essential for a clean weld.
A neutral flame uses equal quantities of oxygen and acetylene. This is the standard setting for most welding work because it adds neither excess oxygen nor excess carbon to the weld pool, producing the cleanest results on steel and many other metals.
An oxidizing flame has a higher proportion of oxygen. The extra oxygen makes the flame hotter and more focused, but it can introduce oxygen into the molten metal, which causes porosity and brittleness in steel. It has limited, specialized uses.
A carburizing flame (sometimes called a reducing flame) has more acetylene than oxygen. The excess carbon in the flame can be useful for specific applications like hard-facing, where you intentionally add carbon to a metal surface, but it is unsuitable for general steel welding because the extra carbon weakens the joint.
Metals and Thickness Range
Oxy acetylene welding works best on metals with relatively low melting points or on thin sections. Steel is the most common material welded this way, but the process also handles aluminum and copper. For thicker steel plate, arc welding methods are faster and produce stronger, more consistent joints. On thin sheet metal, though, the gentle, controllable heat of a gas flame is a real advantage.
The specific nozzle tip, gas pressure, and filler rod you need all depend on the thickness of your workpiece. Equipment manufacturers like Victor publish detailed tip charts that match metal thickness to the correct nozzle size and pressure settings. Checking the chart before you start saves time and prevents problems like burn-through on thin stock or insufficient penetration on thicker pieces.
Where It’s Still Used Today
Modern welding relies mostly on arc methods (MIG, TIG, and stick welding) because they are faster, more efficient, and better suited for producing strong, consistent welds on a production scale. Oxy acetylene has not disappeared, though. It fills roles where its unique characteristics give it an edge:
- Maintenance and repair. Small-scale repair jobs, especially on older equipment or thin-gauge metal, benefit from the precise heat control a gas flame provides.
- Portable cutting. On-site metal cutting in locations without electrical power is straightforward with an oxy acetylene rig, since the equipment runs entirely on bottled gas.
- Heating and brazing. Manufacturing lines that require manual or semi-manual heating, bending, or brazing often use oxy acetylene torches for their adjustable, localized flame.
- Artistic metalwork. Sculptors and ornamental metalworkers favor the process because the flame can be feathered to extremely low heat, giving fine control over thin, decorative pieces.
The equipment is also relatively inexpensive compared to a full arc welding setup, which makes it a practical entry point for hobbyists and small shops that do occasional welding and cutting.
Safety and Cylinder Storage Rules
Working with pressurized, flammable gas demands respect for a few non-negotiable safety rules. OSHA regulations spell out storage and handling requirements in detail.
Oxygen and fuel-gas cylinders in storage must be separated by at least 20 feet or by a noncombustible barrier at least 5 feet high with a fire-resistance rating of at least half an hour. Acetylene cylinders must always be stored valve end up, because the acetone inside can leak into the regulator if the cylinder is on its side. All cylinders should be kept away from heat sources and stored in well-ventilated, dry locations at least 20 feet from highly combustible materials like oil or grease. Valve protection caps should stay hand-tight whenever cylinders are not in use.
Inside a building, the total stored gas capacity is limited to 2,000 cubic feet (or 300 pounds of liquefied petroleum gas) unless the cylinders are in use or connected and ready for use. Even empty cylinders should have their valves closed.
Personal protective equipment for oxy acetylene welding includes welding goggles with the appropriate shade lens, flame-resistant gloves, and clothing that covers exposed skin. The lower intensity of a gas flame compared to an arc means you typically need a lighter filter shade than arc welding requires, but eye protection is still essential to guard against infrared radiation and flying sparks.