What Is Weld Purging?

welding in a workshop

As a welding program student, you come across a lot of specific welding terms, such as annealing, porosity, tension, to name a few.  One of the terms a welding training student needs to know is purging. In short, when you purge a weld, you remove any gases from the welding joint that may impact the weld during or right after the process and lead to oxidation, discoloration, or corrosion. 1

Purging Methods

Gases like oxygen or water vapor are normally removed with inert gases like argon, nitrogen, or helium. The welding torch covers the top of the weld zone with the inert gas, pushing away the unwanted gases. 2 The pressure and flow rate of the purging gas may vary throughout the welding job, so constant monitoring is vital. The quality of the gas may also change during the purging process, and welders should specifically look out for oxygen and moisture levels.

Welding Methods & Purging Gases

The process of weld purging is typically done in GTAW and TIG welding. Argon is the most commonly uses purging gas, but helium can also be used. Nitrogen, however, should not be used on stainless steel. For GMAW, inexpensive carbon dioxide may also be used, as it is a reactive gas. 3 In either case, the gas may not include any impurities like oxygen or moisture 4; otherwise it could damage the molten weld and lead to cracking or brittleness once the material cools down.

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The Importance of Weld Purging

Purging allows for smooth and clean welds that are free from any particles. This precision is especially needed in the semiconductor-, biopharmaceutical- and food equipment industry. 5 Spotless and even contact surfaces are crucial when working with semiconductor materials or biopharmaceutical products. In the dairy sector, for example, full-penetration welds are important for thoroughly cleaning piping systems in dairy plants. 6

If you seek a welding career in a flied that requires high-precision welding, you ought to be familiar with weld purging. Different metals need different kinds of purging gases. Nowadays, monitoring equipment exists that helps you as a welder control the purging process and keep the weld as clean as possible.

Sources:

1 – https://www.huntingdonfusion.com/index.php/en/technical-support/technical-papers-61691/183-advances-in-weld-protection-during-fabrication-of-stainless-steel-tubes
2 – https://www.huntingdonfusion.com/index.php/en/technical-support/technical-papers-61691/250-purging-methods-for-weld-purity
3 – https://www.bakersgas.com/weldmyworld/2015/07/20/purpose-of-purging-in-welding/
4 – http://www.mathesongas.com/pdfs/products/How%20Weld%20Torch%20Hose%20Materials%20Affect%20Shielding%20Gas%20Quality.pdf
5 – http://www.arcmachines.com/news/case-studies/purging-improved-weld-profile
6 – http://www.arcmachines.com/applications/fusion-butt-welding/sanitary-process-piping