In both gas and arc welding, compressed gases are used to shield the molten pool as weld metal gets deposited in the joint. Otherwise, oxidation would occur, allowing air bubbles and impurities to slip into the weld, making it weak.
Here are the most common gases used in different welding processes:
Oxy-Fuel Welding: Oxygen and a fuel gas (Acetylene, Propane, Propylene, Natural Gas, Mapp® Gas) There are also special blends for Oxy-cutting, like MagneGas.
MIG Welding: Carbon Dioxide (CO2), Argon, Helium or blends
TIG Welding: Argon
When you buy a welding machine or Oxy-Fuel kit, you generally have to secure your tanks separately. This allows you to choose between different sizes, depending on how much welding you plan to do. In industrial shops, a manifold is typically set up to control the flow of compressed gases from large tanks to multiple welding station. In a home shop, smaller tanks are set up directly to a welding machine or Oxy torch.
When you take empty tanks into a licensed gas supplier, you’ll surrender them in exchanged for filled tanks that are ready to go. Consequently, the supplier may ask to see your documentation to make sure the empty tanks are in good working order before they accept them. (Keep that in mind should you decide to buy a used tank instead of a new one.)
As a rule, you don’t keep the same tanks over time, although some suppliers will refill them for an additional charge.
There are a few standard protocols to learn before you start working with compressed gases or buy your first Oxy-Fuel welding and cutting kit.
Gas Hoses – In Oxy welding (and in general), the red hose is connected to the fuel, the green hose to the oxygen.
Regulators – These are connected between the tank and one end of the hose. There are two gauges. One tells you how full the tank is. This one is nearest the tank. The second tells you how much pressure is being applied to the gas flowing out of the tank.
When attaching a regulator to a tank, never turn the T-handle all the way in (clockwise) beforehand. This creates unwarranted pressure which can damage the regulator. Instead, turn the handle all the way out (counter clockwise), which is considered the “off” position of the regulator.
Connectors – These are standard “female” and male” coupling hardware on tanks, hoses and torch handles. To make sure there’s no mistake in operator set-up, a fuel tank/red hose connector has a left-handed (counter clockwise) thread. For the oxygen tank/green hose, the connector has a right-handed (clockwise) thread. In both cases, you may need to slightly tighten the connections with a small adjustable wrench to prevent a leak.
Don’t use vice grips on connector. Never use oil or grease (which can combust with oxygen), and never use tape to achieve a tight seal.
Tanks – When not in use, the top of a tank should have a cylinder cap. Keep it fastened to protect the protruding valve (aka snout) from getting banged up. Unused tanks should be stored upright if possible. If they’re laid on their sides, you’ll have to wait awhile after standing them up before you can use them. (Ask your gas supplier for a time recommendation.)
Before attaching a regulator so you can use a tank, first “crack” the cylinder valve. This means standing out of the line of fire, slowly loosening its nut and allowing gas to spew out momentarily, which clears the passage of any dust or debris. Then close the valve and attach the regulator.
While a tank is in use (and even when it’s not in use), keep it secured with a chain or other restraint to prevent it from firing like a missile if the regulator gets detached.
Torch Handle – In Oxy-Fuel welding, both check valves and flashback arrestors should be part of the handle fittings where the hoses connect. A check valve prevents oxygen and fuel from mixing inside the hoses. A flashback arrestor prevents the torch flame from traveling up the hose and into the tank. Never weld or cut with a torch that doesn’t have this hardware in place.
Checking for Gas Leaks
After you tighten your tank connections, always take a moment to investigate your set-up for anything amiss. There might b a ripped hose, defective (or missing) hardware, or a leak. In the latter case:
- Examine the regulator gauges for any sign of needle movement
- Listen for the sound of gas escaping
- Moisten the connections with water (not oil) and try to detect air bubbles, just as you would in a flat tire tube.
Here’s a diagram of a complete Oxy-Acetylene set-op:
Safety Rules for Compressed Gases
Contents under pressure are considered hazardous. If a regulator or valve is dislodged, the sudden burst of gas can turn a steel cylinder into a deadly missile. Gas fuels are combustible and capable of causing third-degree burns in an instant. They can also ignite a shop fire. Long-term inhalation of any toxic gas can produce adverse health effects or be fatal.
Because of these hazards, any employee or hobbyist should be fully briefed on all the safety protocols beforehand. While accidents are rare, they’re next to non-existent when informed workers act responsibly.
The official regulation for compressed gases is known as American National Standards Institute (ANSI), Z49.1-1967, “Safety in Welding and Cutting”.
Here are some of the highlights:
- Cylinders shall be kept far enough away from the actual welding or cutting operation so that sparks, hot slag, or flame will not reach them.
- Cylinders shall be placed where they cannot become part of an electrical circuit. Electrodes shall not be struck against a cylinder to strike an arc.
- Fuel gas cylinders shall be placed with valve end up whenever they are in use. They shall not be placed in a location where they would be subject to open flame, hot metal, or other sources of artificial heat.
- Cylinders containing oxygen or acetylene or other fuel gas shall not be taken into confined spaces.
- Cylinders, whether full or empty, shall not be used as rollers or supports.
- No person other than the gas supplier shall attempt to mix gases in acylinder.
- The cylinder valve shall always be opened slowly to prevent damage to the regulator.
- For quick closing, valves of fuel gas cylinders shall not beopened more than one full turns.
- When a special wrench is required, it shall be left in position on the stem of the valve while the cylinder is in use so that the fuel gas flow can be shut off quickly in case of an emergency.
- Nothing shall be placed on top of a fuel gas cylinder, when in use, which may damage the safety device or interfere with the quick closing of the valve.
- Before a regulator is removed from a cylinder valve, the cylinder valve shall always be closed and the gas released from the regulator.
- Oxygen cylinders should be stored separately from fuel cylinders.
Oil and Grease Hazards
- Oxygen cylinders and fittings shall be kept away from oil or grease. Cylinders, cylinder caps and valves, couplings, regulators, hose, and apparatus shall be kept free from oil or greasy substances and shall not be handled with oily hands or gloves.
- Oxygen shall not be directed at oily surfaces, greasy clothes, or within a fuel oil or other storage.