Shielding Gas and Weld Pool Contamination

Weld pool shielding is certainly a broad topic and while we in no way are trying to cover all aspects of shielding and shielding gas in this article, we would like to talk about some of the basic principles of weld pool shielding, shielding gas, and how contamination can occur.

Why is shielding necessary?

We live in a world that contains atmospheric gases. These gases are useful for combustion, photosynthesis, and breathing, however when it comes to a welding arc and molten metal, our atmosphere is harmful and can cause contamination

It is for this reason we are required to isolate our molten weld pool and our welding arc in a “bubble” of “shielding gas” if you will. The idea is simple, by adding an inert gas of our choosing to the weld pool, we can effectively displace the atmospheric gases that exist in an near the weld pool.

The gas we choose to do the job of weld pro shielding must contain certain properties that prevent it from interacting or chemically changing the weld pool. These types of gases are known as INERT gases. The term (Inert) in this use is defined as “Not reacting chemically.”

Using a shielding gas that is NOT inert could cause many different types of reactions. For example. If you tried to use pure oxygen to shield a weld, the O2 would augment the combustion of the weld pool. The arc would be out of control, unstable, the arc would be too hot, and you would likely melt your torch and your base material rather quickly. 

For this reason, it is important that we use an inert gas such as Helium, Argon, or C02. These types of gases do not react with the weld pool and are very good at simply displacing atmospheric contaminants and providing a stable shielding “bubble” surrounding the weld. 

How is shielding provided?

Shielding to weld pools can be provided in several different ways. The TIG process provides shielding gas from a high pressure cylinder, down a gas hose, and out the nozzle of the TIG torch. The STICK (SMAW) welding process provides shielding to the weld pool through burning a flux coating on the exterior of the electrode. As this flux coating burns, it releases gas that protects the weld pool from contamination.

MIG is a process with a solid wire, where shielding gas is provided down a hose to the nozzle, however when switching to “flux cored” welding wire, you are often able to remove the shielding gas because the flux cored wire contains flux internally that burns and creates a shielding cloud to protect the weld. 


So what happens when you don’t have adequate shielding? Poor weld quality due to contamination can range from obvious porosity to underlying contaminates that were not removed from the weld because of lack of shielding or incorrect flux composition. These aren’t the only variables that can introduce contamination into a weld.

Wind is an outside force that is often overlooked when it comes to welding. Depending on the process you are using, wind can quickly removing shielding from around your weld pool and cause contamination. SMAW or Stick welding is a great process for windy environments. The flux in stick electrodes produces a thick smoke Shield that can be used even in windy conditions.

Contrary to this, the Gas flow rate on TIG welding and MIG welding are such that even the slightest breeze can remove the shielding from around the weld pool. It is important to keep in mind that Flux cored wire, and SMAW electrodes run much better in windy environments, and if MIG or TIG are required, setting up a wind blocking system is a must.

In conclusion

If you are melting metal, it is important to have shielding to protect your weld from contamination. While each welding process differs in how shielding is provided, understanding that our atmosphere is bad for your weld, and applying correct shielding gas or fluxed electrodes is key to achieving a high quality weld. 

Be sure to adjust your shielding gas to the correct rate so that adequate shielding is occurring over your weld pool. Use the correct electrode for your environment, and don’t be afraid to build a windscreen! Being mindful of shielding will help your welds tremendously!