Last Updated on January 2021
Welding gases are gases produced or used during welding and cutting processes. These gases are used to shield the arc from impurities like air, dust, and other gases; keep welds clean on the underside of the seam opposite the arc (or purging), and to heat metal. When deciding the type of gas that you would like to use, it is best to seek expert advice from one or more of the following:
- Follow manufacturer’s instructions; they will give a few choices ranging from the best to something basic without compromising the quality of work
- Seek advice from a welding supplies store as they know how to match gases with the proper welding wire that you plan to use
- Read the product usage guide inside the packaging and safety data sheets to understand and minimize hazards that may occur from welding gases.
It is critical to choose the proper gas welding tank for use because it can dramatically improve the quality, speed, and deposition rate of a given welded item. The type of gas is a determinant of the mechanical properties of the weld, features of the welding arc, and how deep the weld penetrates the metal.
There are only three types of pure gases used in the shielded arc welding processes. These are argon (Ar), Helium (He), and carbon dioxide (CO2). The primary purpose of adding other gases such as oxygen (O2), nitrogen (N2), and hydrogen (H2) is to modify arc characteristics, the molten weld pool, or the weld.
Categories of Gas Uses in Welding
Purging gases – used to cover the underside of the material you’re welding. It is applied mostly on stainless steel items.
Heating gas – certain types of welding require preheating of the metal before the actual welding. This gas comprises a fuel mixed with air or oxygen, which is lit by a flame to heat the metal.
Blanketing gas – this is a process of filling tanks and confined spaces with gas after completion to keep air and other foreign material from contaminating the finished product.
Types of Welding Gases and Their Use in Welding Fabrication
Argon (Ar) is a colorless, odorless, tasteless, and non-toxic monoatomic gas that is chemically inert, hence suitable for welding on reactive or refractory metals. Argon gas has a smooth fluid like arc with a wide but penetration. It is a noble gas comprising 0.93 % of the earth’s atmosphere.
- Casting industry – used to flush porosity from molten metals to eliminate defects in castings.
- Metal fabrication industry – used to create an optimized atmosphere during open arc welding and create an inert gas shield during welding. It is used in both the primary welding stage and to purge the backside of the joint
- Gas Metal Arc Welding (GMAW or MIG) – used to enhance the arc characteristics and facilitate stable metal transfer in Helium by blending it with carbon dioxide (CO2), hydrogen (H2), Helium (He) or Oxygen (O2)
Helium (He) is a colorless, odorless, tasteless, non-toxic, and monatomic gas that is inert and commonly used for GTAW on nonferrous materials. Helium is non-flammable and has high thermal conductivity and ionization potential
- Helium produces a very hot weld with good weld productivity and mild penetration with a fluid arc.
- To create an inert gas shield and prevent oxidation during welding of metals such as aluminum, stainless steel, copper, and magnesium alloys.
- Increases weld pool fluidity and travel speed.
- Addition of Helium to the shielding gas mixture enhances deeper penetration, faster travel speeds and brings a higher heat input to welds
- Reduces the formation of welding ozone when welding on aluminum alloys.
- As a shielding gas, in both its pure form and as a mixed solution with other gases in MIG and TIG welding
- It creates the right mix when used with argon. The argon excels in consistent arc starts, and the Helium adds the extra heat needed for specific applications like welding aluminum, and TIG welding in particular.
- Carbon Dioxide
Carbon dioxide (CO2) is a tasteless, colorless, odorless, non-flammable gas usually used for GMAW short-circuit transfer and FCAW.
- In its pure form, it is used in flux core welding, some carbon steel MIG welding, and plasma shielding.
- When mixed with argon, it can be used as a shielding gas during the welding of carbon and stainless steel. Sometimes it is used in its pure form, therefore helping to prevent atmospheric contamination of molten weld metal during gas shielded electric arc welding process.
- Produces a deep narrow penetration with a stiff harsh arc that works well in out of position welding.
- Adding Carbon Dioxide to Argon or Helium deepens penetration and stiffens the arc improving out of position welding.
- Combining carbon dioxide with oxygen gives a comprehensive penetration profile at the surface of the weld, while the low ionization potential and thermal conductivity create a hot area at the center of the arc column resulting in a well-balanced width-to-depth penetration of the weld.
Acetylene (C2H2) is a colorless, highly flammable gas mostly used for oxy-fuel cutting and brazing applications.
- Has the hottest flame temperature of up to 6,300 °F/3,480 °C, therefore, an excellent choice for welding, brazing, and cutting of steel alloys.
- Used as fuel for oxy-cutting and oxy-welding. When mixed with oxygen, it’s the most effective gas to form a flame hot enough to cut and weld most metals with ease.
Propane (C3H8) is a colorless, flammable, liquefied gas with a distinct or natural gas odor. The flame temperature of the oxy-propane flame is lower and releases lower BTU compared to propylene and acetylene.
- It is commonly used by scrap yards for cutting of carbon steel where the cut quality is less critical.
- It can also be used as cost-effective fuel gas.
Propylene (C3H6) is a colorless, flammable, liquefied gas with a faintly sweet odor. It has moderate BTU capacity in its primary flames and high BTU capacity in its secondary flames.
- It offers more excellent safety as it can be utilized up to full tank pressure.
- With a more significant vapor pressure compared to propane, it is well suited for use at cold temperatures as
- Combines the qualities of an acetylene flame with the secondary heating capacity of propane; therefore, the fuel gas burns hotter than propane. However, before choosing it as a fuel gas, compare the cutting speed based on individual cases.
Oxygen (O2) is a colorless, odorless, and tasteless gas comprising 21% of the earth’s atmosphere.
- Oxygen supports combustion, which amplifies heat with fuel for gas welding and oxy-cutting metals oxy-fuel cutting operations.
- When you mix oxygen with carbon dioxide and argon, it provides wetting and spray advantages
- It is beneficial if added in small quantities to shielding gases benefits as it adds fluidity to the molten pool and speed to the welding process.
- It is used as the plasma cutting gas (with Hafnium electrodes) on carbon steel.
- When mixed with acetylene, it creates the only flame hot enough to weld steel.
- Gas welding with oxygen also provides a sufficient shield to protect some metals from needing a shielding flux filler wire.
Hydrogen (H2) is the lightest of all gases. It is colorless, odorless, tasteless, non-toxic and exists as a gas at atmospheric temperatures and pressures
- Mainly used with austenitic stainless steels to promote oxide removal and increase heat input. Hydrogen may be used in higher percentages of 30 – 40% in plasma cutting operations on stainless steel to increase capacity and reduce slag.
- In metal fabrication, hydrogen serves as a protective atmosphere in high-temperature operations such as stainless steel manufacturing
- Commonly mixed with argon for welding austenitic stainless.
- Used in atomic hydrogen welding which is a specialized process used to weld materials with extremely high melting points, like tungsten
Nitrogen (N2) is a diatomic gas comprising 78% of the earth’s atmosphere. It is colorless, odorless, tasteless, non-toxic, and non-flammable gas, which exists at atmospheric temperatures and pressures.
- Mainly used for the promotion of austenite and to improve corrosion resistance in duplex and super duplex steels.
- Small additions to argon based shielding gases can be used for welding stainless steel by the Gas Metal Arc Welding (GMAW or MIG) process.
- It is utilized as a purge gas with stainless steel tube welding.
- Nitrogen can enhance plasma cutting and heat-treating.
- Used by itself as a shielding gas for laser welding and plasma cutting
- When shielding nitrogen-rich metals, it increases the alloy’s mechanical properties and can deepen penetration while stabilizing the arc.
- It is used as a blanketing gas once welding is finished inside tanks and enclosed spaces, to preserve the material until it is used with its intended product.
Nitric Oxide When added, it serves to reduce the production of ozone and also stabilize the arc when welding aluminium and high-alloyed stainless steel
Other Gases Used in Mixtures in Welding Fabrication
Here are the most commonly used gas mixtures that enhance performance:
Mainly used for conventional and pulsed spray transfer on clean, plain Carbon and Stainless Steel.
- Suitable for welding substantial section Carbon Steel for farm equipment, military transports, ships, and automotive assemblies.
- It is used for spray arc welding of both ferritic and austenitic Stainless Steel components.
Argon-Helium-Carbon dioxide Blend
This tri-mix blend is mainly useful for short-circuiting transfer welding of Stainless Steel in all welding positions.
- Low carbon dioxide content to minimize carbon absorption and assure excellent corrosion resistance, especially in multipass welds.
- Argon and carbon dioxide combination provide excellent arc stability and depth of fusion.
- High helium content provides significant heat input to overcome the sluggish nature of the stainless steel weld pool.
Argon-Carbon Dioxide Blend
Are versatile mixtures for welding Carbon, Low-Alloy, and some Stainless Steel. Increasing the CO2 content will increase weld penetration and bead wetting characteristics.
- Lower levels of CO2 can be used for a pulsed arc or spray arc welding, while higher concentrations (over 20%) are suited for short arc welding and the shielding of some flux-cored wires.
Suitable for producers who join varying thicknesses of carbon, low alloy, or stainless steels using the MIG/MAG process
- To enhance arc performance during welding hence high-quality welds.
- Increases welder productivity
- Produces good weld metal bead shape
- Offers excellent weld mechanical properties while lowering your cost per foot of weld.
Useful in a wide variety of Gas Tungsten Arc Welding (GTAW or TIG) applications where increased heat input to the base material is desirable while maintaining favorable arc starting and stability characteristics.
- Useful for thick aluminum sections and for other nonferrous materials where additional heat input to the base material enhances welding performance.
- It is used for TIG welding of light gauge steel, stainless steel, and aluminum applications such as bicycle frames, food service equipment, and recreational boats.
This combination yields good weld shape and color and increases welding speed in short-circuiting.
Nitrogen increases arc stability and penetration and reduces distortion of the welded part.
Assists in maintaining proper nitrogen content in duplex stainless steels
Can be added to shield gas for aluminium welding to bind hydrogen in the weld area and reduce weld porosity
It can be used for protective atmosphere for the melting of aluminium-lithium alloys. It reduces the content of hydrogen in the aluminium weld, preventing the associated porosity.
You can take several approaches to select a gas, but to make the best selection, you must be sure of what your finished weld requirements and applications are, by answering the following questions:
- What kind of material must be joined?
- How vital is weld appearance?
- Is spatter a concern?
- Is productivity improvement a prime interest?
- Is deep penetration required, or should penetration be minimized to reduce burn-through in the joint?
- Is it essential to reduce welding fumes?
When you have proper answers to these questions, you will not go wrong as you choose the gas best suited for your welding needs.