It is important to select the welding process and materials carefully before you weld stainless steel pipe and tubes because their corrosion resistance can be compromised if sufficient precautions aren't taken. This article discusses some measures that inexperienced welders can take in order to preserve the corrosion resistance of the stainless steel tubes that they wish to weld.
Pay Attention to the Filler Metal
The filler metal that is used when welding stainless steel tube can compromise its corrosion resistance if that filler metal isn't carefully selected. The best filler metals for this welding process should be low in carbon. Such filler metals usually have the letter "L" included in their name to denote their low carbon content. Trace elements, such as sulphur, tin and phosphorous can also affect the corrosion resistance of stainless steel. Select a filler metal with low levels of those trace elements.
Beware of Sensitisation
Stainless steel relies on its chromium content for protection against corrosion. Sensitisation refers to the chemical processes by which this chromium layer is prevented from doing its work. For instance, high temperatures can enable the chromium to react with carbon and air to form chromium carbides. These new compounds eat up the chromium that was available to protect the steel from corrosion. Sensitisation can be prevented in three main ways.
First, the use of fillers with low carbon reduces chromium carbide formation as earlier mentioned. Secondly, using the lowest heat intensity during the welding process can reduce the chance that chemical reactions will take place to form chromium carbides. Finally, some filler metals have ingredients, such as titanium, which prevent any reaction between carbon and chromium.
Use Specific Shielding Gases
The use of nitrogen as a shielding gas during stainless steel tube welding can result in the reduction of the corrosion resistance of the material due to the formation of nitrides. However, argon has no impact on the corrosion resistance of stainless steel. Helium is also good for welding stainless steel. You should select shielding gas combinations that will not have an adverse impact upon the corrosion resistance of the tubes that you wish to weld.
Many more precautions, such as avoiding using tools that have been used on carbon steel, are also necessary to protect the integrity of stainless steel at all stages of the welding process. Ask experienced welders for help in case you keep getting reports of corrosion in the stainless steel pipes that you use during fabrication processes.