Novice Knowledge – What You Need to Know About Welding Gases

For those unfamiliar with welding techniques and equipment, some of the most common misunderstandings involve welding gases. Perhaps it’s decade of seeing old-timers strike up a torch to melt some lead into a seam. Or maybe the sight of all those sparks flying anytime one of their favorite celebrity car builders is repairing a panel. Either way, the assumption is often that welding is essentially the same as working with a hydrogen bomb. And that’s not really the case. Usually.

It’s true that traditional oxy-acetylene “torch” welding uses combustible fuel to join metal with immense heat. However, most welding these days is actually done using an electric arc shielded by a cloud of inert, non-combustible gas. This is called gas arc welding, and the type of gas used depends on the metals being joined. And even though both processes make a lot of sparks, they go about the task of welding in entirely different ways.

Welding with Gas

There are three main welding processes that use some form of gas to get the job done. These include oxy-fuel welding, metal inert gas (MIG) welding, and tungsten inert gas (TIG) welding. The first uses a mixture of two gases to create an intense flame to melt the metal. The other two use different inert gases to shield an electric arc during welding to prevent contamination.

As the name implies, oxy-fuel welding blends a fuel gas with oxygen to create a hot, controlled flame. Acetylene (C2H2) is the most common fuel gas used, and the process is called oxy-acetylene welding. Acetylene is a highly flammable and explosive, requiring care when handling. Precise ratios of oxygen to acetylene come together in a torch head to allow optimum heat control. Other fuel gases for welding include propane (C3H8) which burns cooler but is safe to handle, and MAPP, a combination of methylacetylene and propadiene used in certain cutting and brazing processes.

Metal inert gas welding, or MIG, is a more popular welding method today than oxy-fuel welding. This process is also sometimes referred to as metal gas arc welding, or MGAW. It uses electricity to create an arc between a positively charged filler wire and negatively charged work piece. To prevent oxidation from forming between the various piece of molten metal, the work area is immersed in an inert gas. MIG welding allows you to join various metals including steel, stainless steel, and aluminum. Because each metal has unique properties, the type of shielding gas used depends on the materials.

Tungsten inert gas welding, commonly known as TIG welding, is very similar to MIG welding. Also called tungsten gas arc welding, or TGAW, it applies a positive charge to a fixed electrode made of tungsten metal. This creates a hot electric arc between the electrode and the negatively charge work. The heat of the arc is capable of joining two pieces of metal without adding any material, unlike MIG welding. Filler material can also be added to the arc to build up a bead. As with MIG welding, a cloud of inert gas protects the weld area from corrosion during the process.

Typical shielding gases for steel and stainless steel include argon (Ar) or carbon dioxide (CO2) in a blend. Welding aluminum may require 100% argon or helium (He) depending on the process.

Storing and Handling Welding Gases

Regardless of whether you’re working with fuel gas or shielding gas, you’re going to be working with a high-pressure storage tank. It’s important to handle gas bottles properly to avoid damaging the cylinders. A puncture could result in a catastrophic rupture that can severely injure you.

Always store bottles upright and ensure they’re securely fastened to a wall, bench, or cart to prevent falling over. Keep their valves closed when not in use to avoid losing gas. In the case of combustible gases, an open valve can create a fire hazard. These should always be stored away from heat sources such as furnaces.

When transporting gas bottles, it is best to position them upright if possible. This reduces the chance of damaging the valve assembly. Secure the bottles so they can’t roll or tip, and ideally move them in pickup truck or van. If you must use a car for transporting them, it is recommended you place them in the passenger compartment. Passenger compartments have better ventilation than an enclosed trunk in the event of a leak.

Obtaining and Maintaining a Gas Bottle

So how do you get a gas bottle? Your best bet is to find a local welding supply store such as Airgas or Linde. These retail providers will typically rent you a gas cylinder that can be refilled as you use the gas. Expect to pay a bottle deposit to get started, plus the cost of the first fill. Depending on the vendor, you may be charged a monthly or annual rental fee for possessing the bottle.

As you use your welding gas, you’ll either exchange your cylinder for a pre-filled unit or refill the empty cylinder. This exchange program usually works the same as propane BBQ tanks exchanges. Exchanging bottles, at least periodically, is a great way to ensure the integrity of your cylinder.

Bottles refilled under exchange are often inspected for damage and checked for leaks before they’re shipped out for resale. Your local welding shop performing a refill on the spot may not catch minor damage.