Preventing Porosity in TIG Welding: Tips and Techniques

Tungsten Inert Gas (TIG or GTA) welding is a precise and versatile welding process, known for its ability to produce high-quality welds on various metals. However, like any welding technique, TIG welding can encounter issues, one of which is porosity. Porosity in welds refers to the presence of small cavities or voids within the weld bead. It weakens the weld and compromises its integrity. In this article, we'll explore some of the causes of porosity in TIG welding and discuss effective strategies to prevent it.

Understanding Porosity in TIG Welding

Porosity can manifest as tiny gas pockets or voids in the weld, which appear as small, round holes. These voids significantly reduce the weld's strength and make it more susceptible to cracking and failure. It can result from various factors and conditions during the welding process.

Porosity in TIG welding is primarily caused by the entrapment of gases, such as hydrogen, nitrogen, oxygen, and moisture, within the molten weld pool.

Causes of Porosity in TIG Welding

To prevent porosity effectively, it's essential to understand the common factors that contribute to its occurrence:

Contaminated Base Metal: Dirty or contaminated base metals, including rust, oil, grease, paint, or mill scale, can introduce impurities into the weld pool, leading to porosity.
Improper Gas Shielding: In TIG welding, a shielding gas (typically argon) is used to protect the molten weld pool from atmospheric contamination and oxidation. Inadequate or inconsistent shielding gas coverage can allow air to infiltrate the molten metal, causing oxidation and porosity.
Dirty Electrodes: Tungsten electrodes should be clean and free of any contaminants, as impurities can vaporize and enter the weld pool.
Tungsten Electrode Type: In terms of porosity in the weld, the choice of tungsten electrode can indirectly influence it. Proper tungsten preparation, including grinding and maintaining a clean electrode tip, is crucial for achieving a good weld. Contaminated or improperly prepared electrodes can introduce impurities into the weld, potentially leading to porosity.
Welding Speed: Welding too slowly can increase the dwell time of the molten pool, allowing more time for gases to escape from the base metal and contaminate the weld.
Gas Flow Rate: Incorrect gas flow settings, either too high or too low, can affect the quality of shielding gas coverage and lead to porosity.
Gas Purity: Using low-purity or contaminated shielding gas can introduce impurities and gases into the weld, contributing to porosity.
Inadequate Preparation: Poor joint and edge preparations, including gaps, variations in joint thickness, or improper bevel angles, can create areas where gases become trapped during welding.
Welding Technique: Inconsistent or improper welding techniques, such as excessive weaving or improper travel speed, can lead to uneven gas coverage and potential porosity.

Tips for Preventing Porosity in TIG Welding

Preventing porosity in TIG welding requires careful consideration of the factors mentioned above. Here are some tips and techniques to help you achieve porosity-free welds:

Proper Cleaning: Ensure that the base metal, the tungsten electrode and filler material, is free from contaminants. Use appropriate cleaning methods, such as wire brushing on the base metal and a solvent such as acetate on the filler rods.
Correct Gas Flow: Set the shielding gas flow rate according to the manufacturer's recommendations and monitor it throughout the welding process. Proper gas flow ensures consistent coverage and protection.
High-Quality Shielding Gas: Use high purity shielding gas to minimize the risk of introducing impurities into the weld pool. Verify the gas quality with a reputable supplier.
Selecting the Right Tungsten Electrode: Choose the appropriate tungsten electrode type for your specific welding application. Pure tungsten electrodes are commonly used for AC welding of aluminium, whilst ceriated or lanthanated electrodes are typically used for steels.
Optimal Welding Speed: Maintain a consistent and appropriate travel speed to ensure a consistent shroud of shielding gas and a consistent weld.
Proper Technique: Adhere to proper welding techniques, such as maintaining a consistent torch travel angle. Practice steady and controlled movements for a smooth, even weld.
Gas Cup / Gas Lens: Using a gas lens gives a directed, laminar flow of gas, providing better coverage and also allows the use of a longer electrode stick out for accessing narrow gaps. Use the correct sized gas lens to ensure complete coverage of the weld pool.
Joint Preparation: Ensure the joint is clean, free from dirt, oil, and swarf. Ensure consistent gaps and bevel angles and a good fit up.
Back Purge: In situations where the backside of the weld cannot be accessed, consider back purging to displace atmospheric gases. Back purging involves introducing inert gas on the backside of the joint to maintain a shielded environment.

Conclusion

Porosity in TIG welding is a common issue, but with proper knowledge and careful attention to key factors, it can be effectively prevented. Cleanliness, appropriate gas shielding, electrode selection, and sound welding techniques are essential for achieving porosity-free welds. By following the tips and techniques outlined in this article, you can produce high-quality TIG welds with the confidence that your welds will be strong, durable, and free from porosity-related defects.

For further insights into TIG welding, make sure to explore the following articles on ESAB University: