If you are performing a welding operation, you’re familiar with the term “purging,” which is simply the method of extracting oxygen from the welding scene to avoid the risk of oxidation. When TIG welding, purging prevents issues like pitting, cracking, and splatter from arising. Argon, the most notable purging gas, can be effectively used with steel, aluminum, or copper alloys. In the case of stainless steel, however, the need for purging gas may vary.
Given the different types of stainless steels, inert gases like nitrogen or helium may also be options. In this article, we will discuss these purging gases and determine the best gas for purging stainless steel during welding.
Stainless Steel and Weld Defects From Poor Welding
Welders prefer a TIG welding process for stainless steel to create strong, corrosion-resistant joints. Argon is often used as the shielding gas to protect stainless steel pipes from the external environment during welding. This general mechanism would also work for metals like carbon steel or aluminum. However, when welding stainless steel pipes, chromium content can oxidize along the back of the weld and create a “sugaring” effect. This is observable as the granulation on the backside of the weld and can be the source of cracks, contamination, and corrosion.
Consequently, purging is an important preventive measure against oxidation and contamination on the backside of the weld. The use of inert gas prevents the chemical interaction with the molten puddle to help derive the desired weld attributes. For stainless steel pipes used across food processing, pharmaceutical, oil and gas, nuclear, and many other industries, purging allows for welds that meet both strength and sanitary requirements.
Types of Purge Gases Suitable for Stainless Steel
A common question welders face is: “What gas is best to purge stainless steel pipe during welding?” Popular options include argon, helium, and nitrogen. Below, we explore each of these gases in more detail.
Argon: Argon is the most commonly preferred purging gas by welders when using a TIG or manual welding method. It provides the necessary blanket when welding stainless steel pipes to prevent contamination. Its inert nature prevents oxidation and helps preserve the corrosion-resistant property of the metal while providing a clean and smooth finish. Most standard argon used for industrial welding is 99.99% pure, but 100% pure argon can be used for high-purity applications. Due to its non-reactive nature, it is suitable for high-temperature welding applications.
Nitrogen: Nitrogen is a reactive gas that when combined with heat can enhance the properties of the joint and prevent weld oxidation. Although undesirable for use with most stainless steels, nitrogen has been used in place of argon to purge some stainless steel types. When used with TIG welding for austenitic stainless steel, nitrogen can stabilize the delta-ferrite ratio in the weld pool to improve the tensile strength and pitting resistance in the joint. Nitrogen is also a more economical choice compared to argon. The nitrogen-argon mix can also be used as a purge gas to enhance the weld’s corrosion resistance.
Helium: Helium is a good choice for purging when welding pipes with greater thickness and at high temperatures. However, it is expensive when compared with argon. Helium is often used as a mixture with argon to support high heat requirements during welding and enhance the penetration depth for stainless steel pipes.
Purging to Achieve Clean Stainless Steel Pipe Welds
While the benefits of each purge gas may be different, the aim is to achieve a clean and smooth weld. The choice of gas for stainless steel pipe welding depends on the type of welding application and the desired result. While some applications may benefit from 100% pure inert gas, others may want the reactiveness of the purge gas to enhance the weld properties.
Manufacturers should also consider the purge gas based on welding standards set by different agencies. For instance, the AWS D18.2 specification for welding austenitic stainless steel pipes recommends using argon for purging. Choosing the right purge gas with ideal tools and welding techniques is an excellent way to maximize productivity and improve the quality of stainless steel pipes.
Arc Machines, Inc. specializes in orbital welding technologies that can support your stainless steel pipe welding applications. If you simply want to learn what gas is best to purge stainless steel pipe during welding, or if you need to monitor a high-purity welding application, AMI can help you with a wide range of welding machines and welding purge oxygen sensors. To learn more about our products, contact sales@arcmachines.com. For service inquiries, contact service@arcmachines.com. Arc Machines welcomes the opportunity to discuss your specific needs. Contact us to arrange a meeting.
