Welding Gases: 101 Why We Use It and Their Types

What are welding gases?

Welding gas is used in a range of different ways. These include shielding the arc from impurities like air, dust, and other gases; keeping welds clean on the underside of the seam opposite the arc (or purging); and heating metal. Blanketing gases are also used to protect metal after the welding process.

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.

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

There are two types of gas that is applicable 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—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 welding, like gas welding and brazing, requires 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.

welding gas

The Different Type Of Gas Used For Welding

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

Be sure to evaluate your project goals in order to select the right gas for the weld at hand. Things to keep in mind when selecting are cost, what preparation entails, the base material you’ll be welding, the finished weld properties, and what needs to be done during the post-weld clean-up.

The four most common shielding gases used in MIG welding are Argon, Helium, Carbon Dioxide, and Oxygen. Each provides unique benefits and drawbacks in any given application.

Argon (Ar)

Argon allows for narrower penetration, which is handy for butt and fillet welds. It also boasts a smooth and relatively fluid arc. If you are going to be welding non-ferrous metals, like titanium, aluminum, or magnesium, you’ll need to use pure argon.

Argon is also often mixed with hydrogen, helium, or oxygen. This helps intensify arc characteristics and aid in metal transfer.

If weld quality and aesthetics are important, mixed gases are good to use. You have several options that vary from between 75-95% argon to 5-25% CO2. They produce better arc stability and reduce spatter compared to 100% CO2.

Mixed gases can also be used in the spray transfer process that, in turn, provide more visually appealing welds as well as increased productivity. Argon/CO2 mixtures are good for welding low-alloy, some stainless steel, and carbon metals. Be aware, however, that higher CO2 levels may cause increased spatter.

Helium (He)

Generally used on non-ferrous metals, helium can also be used on stainless steel. It works well with thick metals due to its wide and deep penetration abilities. It is usually used in ratios of 25-75% helium to 75-25% argon.

By adjusting these ratios, you can alter the penetration and bead profile. When used on stainless steels, helium is usually used in a tri-mix gas combination with CO2 and argon. Helium is also used to prevent oxidation during the welding of metals like stainless steel, aluminum, magnesium, and copper alloys.

Helium does create a hotter arc, which provides faster travel speeds and, thus, increased productivity. That being said, helium is more expensive and does require a higher flow rate than argon does. Weighing out the value of the cost of the gas against productivity rates is important to keep in mind when considering using helium.

Carbon Dioxide (CO2)

CO2 is, by far, the most common and is one of the only gases that can be used in its pure form without needing the addition of inert gas, such as argon or helium. Because of this, CO2 is the most cost-effective option and a good choice if project costs are a priority.

Pure CO2, also known as 100% CO2, provides a deep weld penetration, making it handy when needing to weld thick materials. That being said, pure CO2 is limited to only the short circuit welding process and produces a less than stable arc as well as more spatter than when it is combined with other gases (also known as ‘mixed gases’).

Pure CO2 is good for projects where the aesthetics of the weld are either not important, or the weld cannot be seen, such as on the underside of a car. Post weld clean-up is also a little more involved.

Oxygen (O2)

A reactive gas, oxygen is typically used in small amounts when added to shielding gases, usually between 1-9%. This improves weld pool fluidity, as well as arc stability and penetration in stainless steel, mild carbon, and low alloy metals.

It is not recommended to use oxygen with aluminum, copper, magnesium, or other exotic metals since it can cause oxidation.

Oxygen/argon blends are typically used on stainless steel and plain carbon metals. It produces a stable arc with limited spatter. Higher levels of oxygen, however, may make out-of-position welding hard due to the fact that it will increase puddle fluidity.

Nitrogen (N)

Another inexpensive shielding gas, nitrogen increases weld penetration and arc stability when mixed with other gases. These blends can also enhance the chemical properties of alloys containing nitrogen.

Nitrogen is used as a purging gas for welding stainless steel tubes. Added to argon in small amounts, it can also be used as a shielding gas for stainless steel.

Hydrogen (H)

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 misused, hydrogen may cause porosity.

Hydrogen serves as a shielding gas in high-temperature applications, such as stainless steel. It is often mixed with argon for use on austenitic stainless steel.

The Different Type 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 & 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, 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 together. 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 steels
  • 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 level of penetration 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 temperate 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 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 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.