Orbital and Root Gas

Why Is the Use of Shielding Gas in Orbital Welding Important?

Shielding gas is the process of replacing oxygen in the weld zone with a protective gas, such as argon, to prevent corrosion on surfaces heated to high temperatures. However, using poor-quality root gas can pose risks to the welded assembly, and different metals may react in various ways.

Root Gas and Stainless Steel

When welding stainless steel pipes and fittings, it is important to preserve the thin chromium layer that protects the metal from corrosion. Stainless steel is an alloy composed of various elements and contains at least 10.5% chromium. This chromium forms a protective layer of chromium oxide that enhances the durability of stainless steel.

During the welding process, when two stainless steel components are exposed to high temperatures, it is critical that these components remain inert. If shielding gas is not used or if inerting is inadequate, root porosity may form, and the metal may be exposed to corrosion. An unprotected molten pool reacts in a manner similar to that of conventional steel, and in this case, the metal is no longer stainless.

Inerting and Titanium: A Key Property

Titanium and its alloys also face a similar issue. Although lightweight, titanium is an expensive metal that offers a long service life and excellent resistance to substances such as acids, chlorides, and salts. Titanium has the best weight-to-performance ratio among metals.

In titanium welding processes, color distortion resulting from the use of poor root gas is more noticeable than root porosity. As the temperature rises when the material melts, all parts must be maintained in a protective atmosphere throughout the welding process. In the event of root gas defects, the color initially appears golden; when it turns to blue tones, the part is considered damaged. Although some welders mention the challenges of welding titanium, if the correct root gas is used, titanium can be welded even more easily than stainless steel. All titanium alloys are subject to the same rules.

Applications: When Is Root Gas Really Necessary?

It is important to assess whether a root gas is truly necessary before welding. The use of a root gas involves root gas equipment and gas cylinders. If your intention is to weld a simple garden shovel, a decorative piece, or a car bumper, a root gas is unnecessary.

However, if the assembly is designed to carry food products or liquids under high pressure, the use of stainless steel is recommended, and in this case, root gas is mandatory. This applies particularly to “high-purity” industrial sectors such as food and beverage, pharmaceuticals, nuclear energy, and semiconductor manufacturing. In these sectors, the most common welding method is TIG welding (Tungsten Inert Gas welding), which offers excellent control over the molten pool and is therefore well-suited for precision welding.

The various shapes and sizes of workpieces must also be taken into account. While pipe welding is widely used in industrial applications, differently shaped parts such as sheet metal or beams may also require root gas. For example, even if sheet metal vessel bodies are not made of stainless steel, the same principles apply. Similar considerations apply to large tanks; they cannot be completely filled with argon. In such cases, it makes sense to use a U-shaped flange placed behind the weld. This flange will be filled with gas to create a root gas chamber. The goal is to perfectly fill the back side of the weld, which will be exposed to high temperatures. For economic reasons and to speed up the process as much as possible, this procedure should be performed sparingly. For example, if a 1,000-liter tank needs to be filled with gas, significantly more gas will be required to prevent the risk of contamination. For such tasks, it is more advantageous to use an inverted back torch with a large nozzle positioned behind the welding machine.