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Tungsten inert gas (TIG) welding is an incredibly accurate and refined form of welding, using an inert gas shield to help achieve perfection. You might be wondering, though, if you can use Carbon Dioxide (CO2) as your shielding gas for TIG welding.
Can you use CO2 for TIG welding? No, CO2 should not be used for TIG welding because, as it is a gas containing oxygen, it would cause oxidation and result in a bad weld. If either the melted filler material or the metal being welded is allowed to oxidize, the weld will fail.
This may seem like a simple answer, but there are very good reasons for it. Having a good understanding of why this is the case may help you avoid any future mistakes when dealing with shielding gas. In this article, we’re going to go over the best gases for TIG welding and shielding gases in general.
Why Not Use CO2?
TIG welding is performed on stainless steel and other corrosion-resistant metal alloys. These materials are very sensitive to the presence of hydrogen, air, water, and oxygen.
These impurities in the atmosphere can interact with a weld puddle and cause defects such as cracks, reduced corrosion resistance, carbide precipitation, and brittleness.
CO2 is also an active gas and, if an active gas is used for TIG welding, it will raise to arc voltage, increasing hole blows and causing excessive burning of the tungsten electrode. Proper TIG welding needs the right shielding gas.
What is the Purpose of Shielding Gas in TIG Welding?
The main purpose of shielding gas is to prevent exposure of the molten weld pool to oxygen, nitrogen, and hydrogen contained in the atmosphere.
The reaction of these elements with the weld pool can jeopardize a weld and create several issues, including porosity (holes in the weld bead) and excessive spattering when the weld is performed.
To avoid any issues, the right shielding gas needs to be used to push the air in the atmosphere away. Argon, an inert noble gas, is an effective gas to protect the weld puddle.
Why is Argon Used as a Shielding Gas in TIG Welding?
Argon is the third-most prominent gas in our atmosphere (behind Nitrogen and Oxygen). Welders have long relied on Argon for TIG welding because you can use it on all types of metal. As long as you’ve got the right electrode and settings in place, you can expect Argon gas to provide an effective shield for your weld. Other reasons Argon is used in TIG welding include:
- Protection – Shielding gas is necessary for welding because it’s essential to keep Oxygen from the weld pool. An inert gas, such as Argon, performs the essential task of replacing the Oxygen-containing air with itself and protecting the weld. Argon gas envelops and stabilizes the electrical current of the welder to keep the metals from getting oxidized.
- Arc – The arc produced with a pure Argon shielding gas is more stable, narrow and concentrated, giving you a precise weld with significant penetration.
- Look – A weld made from Argon has a bright, shiny appearance. If something other than pure Argon is used, it can result in a duller presentation with a potential need for brushing and polishing. Argon also produces little to no porosity, an optimal weld bead shape, and a strong, stable weld.
Other Gas Options for TIG Welding
Proper shielding gas coverage is critical to achieving the best results in TIG welding. While pure Argon gas is preferred, a few other shielding gas options exist.
Because it has a higher thermal conductivity than Argon, Helium can be used for TIG welding to produce higher heat inputs. Higher heat inputs result in quicker travel speeds and greater depth-to-width ratios.
Helium works well for welding thicker materials (greater than 3/8 inches) because it creates a hotter weld puddle. Pure Helium has a higher ionization potential, though, resulting in inconsistent arc starts.
Argon and Helium mixed together are used to achieve the higher heat inputs of Helium while maintaining the superior arc starts provided by Argon. The mix can contain anywhere from 25 to 75 percent Helium. However, as Helium content increases, the arc becomes hotter but high-frequency arc-starting performance and stability decreases.
Helium can be used for most TIG welding jobs with the exception of mild steel. It can be used for aluminum, stainless steel, and copper alloys.
In some cases, welders working with stainless steel may opt to work with Hydrogen. Hydrogen, much like Helium, increases the heat input while welding.
Typically, five percent or less of Hydrogen will be used in a shielding gas mixture. The advantage to using Hydrogen for stainless steel is superior oxide removal and a hotter, wider bead that penetrates deeper into the metal.
Shielding Gas Flow Rates
Once you choose your shielding gas, you will need to determine the optimal gas flow rate for the perfect weld. TIG welding flow rates are typically between 10 and 35 cubic feet per hour (cfh).
When your shielding gas exits the nozzle, it will have a different velocity than the atmospheric gasses surrounding it. The different velocity and density between the two can cause currents to form.
This can potentially turn the shielding gas column from a laminar flow (which is desirable) to a turbulent flow (which is not desired).
If the flow becomes turbulent, atmospheric gasses can be pulled into the shielding gas column, ultimately leading to contamination of the weld and tungsten. Lowering the cfh will help the shielding gas column to become more laminar.
However, even though a higher flow rate can cause contamination, a meager rate can be simply be disturbed, breaking down the shielding gas column. This breakdown can contaminate the weld and/or tungsten, as well.
You will need to assess your TIG welding flow rate to achieve the highest laminar flow while not allowing a turbulent flow and possible contamination. For best results, choose a flow meter regulator to accurately measure the cfh.
Consumables for Shielding Gas and TIG Welding
Consumables are an important factor in creating quality welds. Keep in mind when choosing TIG welding, Pick torch consumables that offer both:
When practicing welding or non-critical, a collet body will do. A collet body brings the shielding gas to the inside of the nozzle with its 4 holes.
They are able to hold the tungsten right where it is when you tighten the back cap. It makes the electrical contact perfect for good current transfer.
Normally they’re made from standard tellurium copper or standard grade copper. Keep in mind when using the body, that the tungsten shouldn’t push outside the nozzle more than the distance inside the nozzle’s diameter.
If the weld is critical or requires the best quality, a gas lens is the best option. A gas lens boosts shielding gas coverage and cuts down turbulence versus to that of a collet body because it has a couple screens inside that create a more uniform laminar flow. The gas lens enables the tungsten to continue farther than the inside diameter of the standard collet body.
The nozzle (aka the cup) screws onto the collet body or gas lens and popularized the gas to the weld. Nozzles are available in various lengths, diameters, and shapes to produce different shielding profiles or laminar flow lengths.
Nozzle lengths add standard, long and extra-long. Longer nozzles bring longer laminar flow columns compared to smaller nozzles with the same flow rate and cup diameter.
The reason why is because the flow is more developed before leaving the nozzle lessens the shear between the flow and the surrounding atmosphere. Long nozzles also benefit for great access to tighter joints.
Nozzle shapes include straight, converging and champagne. Converging nozzles start with a larger diameter and neck and decrease to a smaller diameter. This shape is recommended to achieve the longest laminar flow.
A champagne nozzle is an opposite shape of converging. This nozzle is not beneficial in TIG welding, as the shielding gas exits at the gas lens or smaller diameter of the nozzle, creating a more turbulent flow.
To get the best laminar flow, be sure to use a converging shape nozzle in the biggest diameter and the longest length practical for your job.
Final Thoughts on CO2 Gas for TIG Welding
In TIG welding applications, choosing the proper shielding gas, along with the correct flow rates and consumables, will help you achieve the best weld. Remember, if you use CO2 as a shielding gas, you risk weld contamination, porosity, and other weld defects.
This article has hopefully given you a broader understanding of why CO2 isn’t a good choice of shielding gas for TIG welding. Instead, using the shielding gas options mentioned above is going to result in a much more quality weld and one that you are going to be proud of.