Welding Gases: 101 Why We Use It and Their Types

Whether you’re welding mild steel, aluminum, or stainless, choosing the right shielding gas is important to getting good results.

Do you have questions about choosing the right welding gas for your DIY welding projects? Whether you’re welding mild steel, aluminum, or stainless, choosing the right shielding gas for the base material is an important first step in getting good results.

Learn more about shielding gas options for welding and get tips for proper setup and troubleshooting common issues.

What are welding gases?

Welding gases are gases used or produced during welding and cutting processes like shielding gases or gases produced by the decomposition of fluxes or from the interaction of ultraviolet light or high temperatures with gases or vapors in the air.

Gases used in welding and cutting processes include:

  • 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 traditional stick welders knew very little about gases with their welding, the rise of the MIG and TIG welding machines over the last 70 – 80 years has brought in the need for welding gas as a common commodity in most workshops.

As we jump into the leading gases and mixtures used in the welding world, it’s fascinating to learn how much we have progressed over the short time since they were first implemented. The progression is enormous, and what’s in store for new gases or new ways to use these gases, is exciting.

In this article, we’ll explore the different types of welding gas and their uses.

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.

Welding Gases

1. Argon (AR)

Pure argon is often used with aluminum and nonferrous metals. This gas is good for shielding flatly-positioned welds and welds in deep grooves.

Used primarily when welding stainless steel and aluminum, argon also works on carbon steel with arc stability and continuous metal transfer from the weld pool’s electrode. Argon is the top choice for TIG welding and an excellent shielding gas for MIG.

Argon is suitable for easier starts, alternating current (AC) applications, and for longer arcs at lower voltages. The addition of helium improves argon’s heat transfer properties and argon mixed with carbon dioxide or oxygen can help stabilize the arc.

2. Helium (HE)

More expensive than other gases, helium provides deep penetration and increases the heat input. Pure helium is ideal for welding magnesium, copper, and aluminum.

While it can be hard to get a consistent arc start with helium alone, it works well when blended with argon while counteracting its inconsistent starting properties.

However, it creates an erratic arc which can result in spatter when working with steel. Helium is effective for mechanized welding but allows less room for error in manual welding.

A helium-argon mixture can be used to clean cathodes.

3. Carbon Dioxide (CO2)

The most common shielding gas for MIG welding, CO2 costs less than argon but does not produce identical high-quality welds. However, when mixed with argon, there is less spatter and better-looking welds.

Carbon dioxide improves weld speed, penetration, and mechanical properties that make it the most suitable for steel in metal inert gas (MIG) welding.

However, this gas also causes a shakier arc, spatter losses, and a lot of smoke fumes. Mixing carbon dioxide with argon minimizes the spatter.

Carbon dioxide should not be used with thin metals such as aluminum that cannot sustain its high temperatures.

4. Oxygen (O2)

Oxygen is typically mixed with other shielding gases because it changes the fluidity of the molten metal. It can also speed up the welding process and minimize spatter.

Oxygen’s oxidizing properties make it unsuitable for working with copper, aluminum, and magnesium. The gas should be used sparingly as too much may cause products to become brittle.

5. Nitrogen (N)

Nitrogen increases weld penetration and arc stability. Nitrogen mixtures can increase the mechanical properties of alloys containing nitrogen and prevent pitting corrosion as well as nitrogen loss from the metal.

These blends can also enhance the chemical properties of alloys containing nitrogen.

6. Hydrogen (H)

Hydrogen can produce cleaner weld surfaces and better bead profiles for grades of stainless steel that are sensitive to oxygen.

When added to argon, hydrogen provides deeper penetration and faster welding speeds. The mixture of hydrogen, argon, and carbon dioxide can improve weld penetration. However, if used incorrectly, trapped gas can cause weld porosity and cracking under 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

Relatively cheap and highly combustible, acetylene combines with oxygen as a fuel source in specific types of welding. By producing a hot flame, it can cut or weld most metals.

8. Propane

Not appropriate for gas welding, propane is used primarily for brazing after the welding process is completed. Propane is a flammable and combustible gas used in many applications as a fuel source.

9. Propylene

While not a pure gas (it’s blended with oxygen), propylene burns at a substantially higher heat than propane and oxygen, making it suitable for non-structural fusion welding, brazing, and heating.

What Is the Purpose of Gas in Welding?

There is a range of different uses for gas in welding. This can include: keeping the arc clear of impurities (such as dust, other gases, dirt, etc.),

Also used for assisting arc stability and ensuring proper metal transfer for many welding processes. Make sure that the welding pool stays clean below the seam (this is known as purging), for blanketing and heating too.

If you don’t use gas properly in welding you can end up with a weak or porous weld or find that there is too much spatter while welding. Spatter won’t ruin the weld but it does reduce productivity as it requires effort to clean it up.

1. Inert and Reactive Gases

Two types of gas applies to welding:

Inert gases. An inert gas is a gas that does not change under a given set of conditions. Inert gases are often used in welding, sealing, or marking applications in an effort to avoid unwanted chemical reactions which may degrade a part. These unwanted reactions include oxidation and hydrolysis which are reactions with oxygen and the moisture in the air.

Purified nitrogen and argon are most commonly used as inert gases due to their high natural abundance (78% N2, 1% Ar in the air) and relatively low cost.

Reactive gases. Also known as inert gases—these are gases that do not undergo chemical reactions under specific conditions such as oxidization. These include argon, carbon dioxide, helium, and nitrogen.

Reducing shielding gases in welding technology are always mixed gases consisting of argon or nitrogen with hydrogen. Argon with hydrogen is used, for example, in TIG welding of stainless steel. Nitrogen and hydrogen are applied as backing gases. Attention: If the proportion of hydrogen is more than 10%, it must be flared because of fire and explosion hazards.

2. Shielding gas

When the air gets into the arc while you’re welding, it causes air bubbles to form within the molten metal, creating a weak and very ugly weld. You cannot MIG or TIG weld without a shielding gas unless the filler material being used is flux-cored or flux-coated. This serves the same purpose as a shielding gas, keeping impurities out, but in a different way.

Most shielding gases are inert, which makes them ideal for shielding a welding process as they remain stable under welding’s extreme conditions. They also nurture the weld in different ways, depending on the gas being used, including more penetration, more fluidity when molten, and a smoother surface on the bead.

3. Purging gas

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

While you weld the top of a joint, the bottom of the joint is sealed off and has a flow of gas purging it. It’s frequently used with stainless steel items, and it can be the same type of gas or a different gas than what’s used on the top of the joint.

4. Heating gas

Certain weldings, like gas welding and brazing, require gas to heat the metal or the filler rods to achieve the welding. This replaces the need for an arc.

Specific types of welding require the metal to be preheated before welding, which this gas is used for. The gas is simply a fuel mixed with air or oxygen, which is lit by a flame to warm or melt the metal.

5. Blanketing gas

Blanketing is a process where tanks and confined spaces are filled with gas after they’re completed to keep air and other contaminants from damaging or staining the finished product.

Sometimes it’s used to fill the completed projects entirely. Other times, the gas is added to the air-filled tank, creating a mixture to keep the tank pure against other gases or reactions.

The Different Types of Mixed Gases Used In Welding

Argon & CO2

The most common mixed gas for shielding in welding is a CO2, Argon Mix. It can run from 95% – 80% Argon and 5% – 20% CO2. In most applications, this will create a pleasantly smooth weld and keep the amount of spatter to a minimum.

The thicker the steel you’re looking to weld, the more Carbon Dioxide you require in the mix, and the thinner it is, the more Argon you need.

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 looking for a little more fluidity in the weld pool then you’re probably looking for an Argon, CO2 gas, and oxygen mix. You get fairly similar properties to the Argon, Carbon Dioxide blend when it comes to the finished weld.

However, in addition to the improved fluidity, it can also improve the travel speed of the welding process and make a welder much more productive. 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

There is a wide range of different mixes available when your chosen weld gas is an Argon, Helium, or Carbon Dioxide mix. Depending on what it will be used for the mix will either be dominated by Helium or Argon.

The gases used, make this mix suitable for welding anything from carbon steel to stainless steel, and it can even be used as an aluminum welding gas. (a good mixture for welding stainless steel with MIG machines)

Argon/Helium/CO2 is best 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’re looking for gas for welding Aluminum then you’re probably going to go with Helium & Argon mixed. In addition to Aluminum, it’s also suitable for welding alloys.

Why? Well because the mix provides a deeper level of penetration and also delivers a wide finish on the weld itself.

We use this mix most commonly in:

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

Argon & Oxygen (o2)

This mix of gases isn’t suited to stainless steel and if you are welding steel with it – it will normally be light gauge steel. Its purpose is to help with the material fusion of the steel.

You won’t normally find very much Oxygen in this argon gas mix because otherwise, it would burn too hot, and argon gas welding is for finer things and thinner 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’re TIG welding with gas then a mixture of Hydrogen and Argon is ideal when you need a clean weld. The hydrogen prevents any oxygen in the air from getting into the weld and causing oxidation.

The waste product of this reaction is water which quickly evaporates under the heat of welding. It helps maintain a narrow and precise arc while increasing heat transmission.

  • Gas tungsten arc welding (GTAW) on austenitic steel

Nitrogen & Hydrogen

This mix has a fairly specialist use and it’s a shielding gas for the preparation of austenitic (that is high in chromium and nickel with low carbon) stainless steels.

It enables a higher penetration level whilst making the welding process go faster. It also helps to improve the mechanical properties of the stainless-steel end 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 very flammable and it is highly combustible in the air. It is very easy to make and fairly cheap to use.

It’s combined with oxygen and used as a fuel source in certain types of welding. It produces a very hot flame that is capable of cutting or welding the majority of metals.

2. Propane

Propane is also very flammable and it is highly combustible in the air. It is better known as LPG (Liquid Petroleum Gas) and is used as a fuel source in many contexts.

It will burn the skin if it comes into contact with it. Surprisingly, however, it cannot be used in gas welding because unlike acetylene when you burn it in oxygen it does not create a reducing zone (that would clean the steel surface as you weld).

It is used mainly for brazing after welding is finished.

3. Propylene

Propylene isn’t actually a pure gas, it’s a blend with Oxygen. It will burn at a much higher heat than Propane and Oxygen will and it’s completely suited for non-structural fusion welding, brazing, heating, and more.

However, it’s generally supplied in small, disposable canisters that aren’t really big enough to enable heating during the welding of large items.

4. Compressed Air

As you might expect compressed air is the cheapest of the gases that are used in welding because it’s air. (Though it is often purified a little). When you mix compressed air with another fuel then it can produce a strong flame at a lower temperature than an oxy-fueled flame. For welders, this means that they can get greater control over the thickness of the carbon coating they 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

  • Inspect equipment for leaks at all connections using the approved leak-test solution.
  • Inspect hoses for leaks and worn places.
  • Replace bad hoses.
  • Protect hoses and cylinders from sparks, flames, and hot metal.
  • Use a flint lighter to ignite the flame.
  • Stand to the side (away from the regulators) when opening cylinder valves.
  • Open cylinder valves very slowly to keep sudden high pressures from exploding the regulators.
  • Only open the acetylene cylinder valve ¼-¾ turn; leave the wrench in place so the cylinder can be quickly closed in an emergency.
  • Open and light acetylene first, then open and adjust oxygen to a neutral flame.
  • Follow the manufacturer’s recommendations for shutting off the torch. If the guidelines are not readily available, the commonly accepted practice is to close the oxygen valve first.
  • When finished, close cylinder valves, bleed the lines to take pressure off regulators, neatly coil hoses, and replace equipment.
  • Have a fire extinguisher easily accessible at the welding site.