Welding Gases: 101 Why We Use It and Their Types

If you’re welding mild steel, aluminum, or stainless steel, selecting the right shielding gas is a big step toward getting a good result.

Do you have questions about how to select the proper welding gas for your DIY welding projects? Whether you are welding mild steel, aluminum, or stainless steel, choosing the right shielding gas for your base material is an important first step toward getting good results.

Learn more about the shielding gas options for welding, tips on a proper setup up and how to troubleshoot some common issues.

What are welding gases?

Welding gases refer to gases that are used or produced in welding and cutting processes, such as shielding gases or gases produced through decomposition of fluxes or by the UV-light or high temperatures interacting with a gas or vapor in air.

Gases used in welding and cutting processes are:

• Shielding gases such as carbon dioxide, argon, helium, etc.
• Fuel gases such as acetylene, propane, butane, etc.
• Oxygen, used with fuel gases and also in small amounts in some shielding gas mixtures

While conventional stick welders typically connect with very few gases during their welding process, the emergence of the MIG and TIG welding machines over the last 70 – 80 years has cemented welding gas as a common product in many workshops.

As we delve into the prevailing gases and mixtures in the welding world, it’s intriguing to see how far we’ve come in such a short time since these products have been implemented. The evolution is immense, and the future with both new gases and uses of these gases will be interesting.

In this article, we will look at the different types of welding gases and how they are used.

Types Of Welding Gases Used for Shielding

The first two shielding gases, argon, and helium are inert, while the other four—hydrogen, oxygen, carbon dioxide, and nitrogen—are semi-inert.

1. Argon (AR)

Elemental argon is commonly utilized with aluminum and nonferrous metals. Argon is effective for shielding flat position welds and welds in deep grooves.

Argon is principally used when welding stainless steel and aluminum. Argon is also workable with carbon steel under good arc stability, allowing for continuous transfer of metal from the electrode into the weld pool. Argon is the best option for use with TIG and is a good shielding gas for MIG.

Pure argon is applicable for easier starts, when using alternating current (AC), and for longer arcs at lower voltages. When used with helium, pure argon has better heat transfer characteristics. Carbon dioxide or oxygen mixed with argon can provide stability to the arc.

2. Helium (HE)

Helium is a more expensive gas and provides deep penetration and increased heat input. Pure helium is the best gas for welding: magnesium, copper, and aluminum.

It can be difficult to establish a consistent arc with pure helium, but it does produce a consistent arc when mixed with argon, as long as the arc starts consistently.

However, helium also can produce an erratic arc while welding steel which can also result in spatter. Helium is useful for mechanized welding but also has less margin for error for manual welding.

A helium-argon mixture can also clean cathodes.

3. Carbon Dioxide (CO2)

Carbon dioxide is not the most common shielding gas for multiple reasons. CO2 costs less than argon but is incapable of yielding the same quality welds as argon. When CO2 is mixed with argon, there is less spatter, and it produces a better-looking weld.

CO2 improves weld speed, penetration and mechanical properties, making it a better value for steel in metal inert gas (MIG) welding.

In addition to the advantages of using CO2 as a shielding gas, it also produces a shakier arc, generates spatter losses and smoke fumes. However, using a mixture with argon will reduce spatter.

CO2 is not a good idea to use at all with thin metals like aluminum that cannot withstand co2 high heat.

4. Oxygen (O2)

Oxygen is usually mixed with other shielding gases due to its ability to change the fluidity of molten metal and to increase the welding speed and reduce spatter.

Because of the oxidizing properties of oxygen, it is not ideal for use with copper, aluminum, and magnesium. The gas should be used sparingly and too much can lead to brittleness.

5. Nitrogen (N)

Nitrogen improves weld penetration and arc stability. Nitrogen mixtures can improve mechanical properties of alloys containing nitrogen and can inhibit pitting corrosion, along with nitrogen loss from the metal.

The mixtures can also improve the chemical properties of alloys containing nitrogen.

6. Hydrogen (H)

Hydrogen can produce cleaner weld surfaces and more suitable bead shapes for oxygen-sensitive grades of stainless steel.

When mixed with argon, hydrogen can produce deeper penetration and improved speeds. A mix of hydrogen, argon, and carbon dioxide can enhance weld penetration, but if done wrong, trapped gas can lead to porosity or a crack underneath the bead in carbon and low-alloy steels.

Other Gases Used in Welding

The following three reactive gases are used in oxy-fuel welding and are highly flammable.

7. Acetylene

Acetylene is inexpensive and very flammable, and is used with oxygen as a fuel for some types of welding processes. It can cut (or weld) most metals by creating a hot flame.

8. Propane

Propane is primarily a fuel for brazing after comparable hot welds and therefore is not proper for gas welding. Propane is used as a flammable and combustible gas in many different scenarios.

9. Propylene

Propylene is not entirely a gas (it is mixed with oxygen), but its heat is much higher than propane and oxygen together and can be used for non-structural fusion welding, brazing, and heating.

What Is the Purpose of Gas in Welding?

There are a variety of different purposes for gas in welding. These can include: Keeping the arc clean of contaminants (like contaminants from the surrounding atmosphere, other gases, dirt, etc. ) used for helping stabilize the arc and facilitate proper metal transfer for many welding processes, too.

To ensure the welding pool is clean beneath the seam (this is otherwise known as purging), blanket and heat.

If gas isn’t used properly in welding, you can end up with a weakened, porous weld, or you’ll see far too much spatter while welding. While spatter doesn’t ruin the weld itself, it does slow your production down because it takes effort to clean it up.

1. Inert and Reactive Gases

Two types of gas applies to welding:

Inert Gases: An inert gas is one that does not change state under a given set of conditions. Inert gases typically find application in welding, sealing, or marking operations to avoid unwanted chemical reactions that may compromise a part.

Such reactions include oxidation and hydrolysis, which are reactions in which oxygen and moisture in the air interact.

Nitrogen and Argon are commonly used as inert gases due to their abundance in the atmosphere (78% N2 and approximately 1% Ar) and cost effectiveness.

Reactive Gases: Also called inert gases they are gases that do not undergo chemical reactions under specific conditions, and oxidization is one of them. They include argon, carbon dioxide, helium, and nitrogen.

Reducing shielding gases are mixed gases in welding technologies consisting of argon or nitrogen mixed with hydrogen. Argon with hydrogen is used, for example, in TIG welding of stainless steel. Nitrogen and hydrogen which are applied as backing gases.

Warning: if the proportion of hydrogen exceeds 10%, it should be flared due to fire and explosion conditions.

2. Shielding gas

When air enters the arc, it creates air bubbles in the molten metal while you’re welding and this creates a weak, and very ugly weld.

Also, there is no way to MIG or TIG weld without a shielding gas, unless the filler material is either flux-cored or flux-coated, which protects the arc in the same way but in a different manner.

The majority of shielding gases are inert, is great for shielding a welding process because inert gases are chemically stable under the extreme conditions of welding.

The shielding gas also supports the weld in some different ways depending on the gas, such as additional penetration, more fluidity when molten, and a smoother surface on the bead.

3. Purging gas

Purging gases are used to cover all the bottom side of the material you’re welding, the same way a shielding gas does, only it is done separately from the natural process of the weld.

When you are welding the top of a joint, the bottom of the joint is isolated and has a flow of gas purging it. It is commonly used with stainless steel materials, and it is possible the gas can be the same gas or different gas than that being used on the top of the joint.

4. Heating gas

Certain welding types, such as gas welding and brazing, rely on a gas to heat the metal or the filler rods being welded. This replaces the arc.

Some types of welding will require the metal to be preheated before welding. The gas is used for that preheating and is just a fuel (gas) mixed with air or oxygen, and a flame is applied to warm or melt the metal.

5. Blanketing gas

Blanketing is an operation that involves filling a tank and confined space with gas following completion to keep air along with other contaminants from affecting or staining the finished product.

Blanketing is sometimes used to fill the completed project completely. Other times, gas will be added to the completed, air filled tank, creating a mixture of air and gas, which will keep the tank pure against incoming gases or reactions.

The Different Types of Mixed Gases Used In Welding

Argon & CO2

The most widely used mixture of shielding gas in welding is a mixture of CO2 and Argon. It can range from 95%-80% Argon, with 5%-20% CO2. In most applications, this will give you a nice smooth weld and significantly reduce the amount of spatter.

Typically, the thicker the steel you are welding, the more Carbon Dioxide you will want in your mix, and the thinner the steel, when you will want more Argon.

Welders use these gas mixtures in:

• Gas metal arc welding (GMAW) on carbon steel
• Flux-cored arc welding (FCAW) on carbon steel
• Flux-cored arc welding (FCAW) on stainless steel

Argon, CO2, & Oxygen

If you’re seeking greater fluidity in the weld pool, then you are likely seeking an Argon, CO2 gas and oxygen mix. You can attain very similar characteristics to the Argon, Carbon Dioxide mixture when it comes to the weld you finish.

In addition to the improved fluidity it can improve the travel speed of the welding and therefore improved productivity for the welder. We use it in the following processes:

• Gas metal arc welding (GMAW) on carbon steel
• Gas metal arc welding (GMAW) on stainless steel in some cases

Argon, Helium, CO2

Of course there are many different mixes available, when your selected weld gas is Argon, Helium or Carbon Dioxide. Depending on the mix of gas, it will either be dominated by Helium or Argon.

Depending of what the mix will be used for, the gases made it possible to welded material from carbon steel to stainless steel, which can also used as an aluminum welding gas. ( a good mix for welding stainless steel with MIG machines)

Argon/Helium/CO2 is good for the following processes:

• Gas metal arc welding (GMAW) on stainless steel
• Flux-cored arc welding (FCAW) on carbon steel
• Flux-cored arc welding (FCAW) on stainless steel

Helium & Argon

If you are looking for a gas for welding Aluminum then you are going to likely go with Helium & Argon mixed. This mixed gas is not only designed to weld Aluminum. It will also work well for welding alloys.

Why? Because the Helium & Argon mix offers deeper penetration and gives a wider finish on the weld.

We most commonly use this mix for:

• Gas metal arc welding (GMAW) on aluminum
• Gas tungsten arc welding (GTAW) on stainless steel or aluminum

Argon & Oxygen (o2)

This gas mixture is not for stainless steel and if you are welding steel with it – generally – it will be light gauge steel. The purpose is to assist in the material fusion of the steel.

You should not usually find very much Oxygen in this argon gas mixture otherwise it would burn too hot, and argon gas welding is used for finer, thinner things, such as materials.

Use argon/O2 mixtures for the following welding processes and metals:

• Gas metal arc welding (GMAW) on stainless steel
• Gas metal arc welding (GMAW) on carbon steel

Argon & Hydrogen

If you are TIG welding with gas, a mixture of Hydrogen and Argon is best when you need a clean weld. The hydrogen inhibits oxygen in the air from getting into the weld and oxidizing.

The waste product of this reaction is water, which evaporates quickly under the welding arc. It helps create a thin and tight arc and improves heat transfer.

• Gas tungsten arc welding (GTAW) on austenitic steel

Nitrogen & Hydrogen

This mixture has a very specialist application as it will be used as a shielding gas for the welding of austenitic (high chromium and nickel and low carbon content) stainless steels.

This allows for a higher penetrability level whilst making the welding process quicker. It is also an aid to improve the mechanical properties of the stainless-steel finished product.

Gases In Oxy-Fuel Welding

The three gases below acetylene, propane, and propylene are used in oxy-fuel welding and are extremely flammable.

1. Acetylene

Acetylene is highly flammable and highly combustible in the air. it is typically easy to make and generally inexpensive to use.

Acetylene is combined with oxygen and used in certain types of welding as a fuel source. Acetylene produces a hot flame capable of cutting or welding most metals.

2. Propane

Propane is extremely flammable and quite combustible in the presence of air; The gas is more appropriately known as LPG (Liquid Petroleum Gas) and is utilized as a fuel source in many ways.

It also burns skin if exposed to it; but, it is surprising that you cannot use it in gas welding since, unlike acetylene, when burnt in oxygen it does not form a reducing zone (that cleans the steel surface as welding proceeds).

It is mainly used for brazing after finishing welding work.

3. Propylene

Propylene is not a pure gas; it is a mixture with Oxygen. It will burn at a much hotter heat than just Propane and Oxygen, and it is completely suitable for non-structural fusion welding, brazing, heating, etc.

The only problem is that it is usually supplied in small, disposable canisters that are too small for heating while welding larger items.

4. Compressed Air

As can be expected, compressed air is the cheapest of the gases used in welding. (Although it is sometimes cleaned up a bit). When compressed air is combined with another fuel, then it is capable of providing a very strong flame at a lower temperature than an oxy-fuelled flame.

For welders, this means they have greater control over the thickness of the carbon coating they can apply to the weld.

Gas Welding Safety

Storage and Handling

• Keep cylinders away from physical damage, heat, and tampering.
• Securely chain equipment to prevent falling.
• Store away from flammable and combustible materials.
• Store extra gas and oxygen cylinders separately.
• Store in an upright position.
• Close cylinder valves before moving.
• Protective caps or regulators should be kept in place.
• Roll cylinders on bottom edges to move—Do not drag.
• Allow very little movement when transporting.

General Gas Welding Safety Tips

• Check the equipment to ensure there are no leaks at any connections using the approved leak-test solution.
• Check the hoses for leaks and for worn spots.
• Replace leaky hoses.
• Protect hoses and cylinders from sparks, flames, and hot metal.
• Use a spark lighter to ignite the flame.
• Stand to the side (away from the regulators) when opening cylinder valves.
• Open cylinder valves very slowly to prevent regulators from exploding under sudden high pressures.
• Only open the acetylene cylinder valve ¼-¾ turn, and leave the wrench in the valve so you can quickly close it in an emergency.
• Only open and light acetylene first, then open and adjust the oxygen to get a neutral flame.
• Follow the manufacturer’s instructions on how to shut off the torch, but if that isn’t available the generally accepted practice is to close the oxygen valve first.
• When you are finished, close the cylinder valves, bleed the lines to relieve pressure from the regulators, coil the hoses neatly, and return the equipment.
• Have a fire extinguisher readily available at the job site.

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