Sensitisation refers to the loss of the chromium content as one is welding stainless steel. This loss of chromium predisposes the stainless steel product to corrosion. Several options are available to welders to prevent sensitisaton from happening as they repair stainless steel tube. This article discusses some of those options.
Use of Low-Carbon Fillers
The first option entails selecting welding fillers that have minimal amounts of carbon in them. Such low levels of carbon will be unable to react with the chromium layer in order to create chromium carbides. Consequently, most of the chromium will still be available to form a corrosion-resistant surface at the weld site on the stainless steel.
However, it may not always be practicable for you to use low-carbon fillers in all stainless steel welding operations. This is because it may be desirable to use carbon-rich filers in order to enhance the strength or other properties of the welded stainless steel tube.
Keep Heat Exposure Low
Sensitisation also occurs when stainless steel is exposed to intense heat for long. That heat accelerates or facilitates the reaction between chromium and carbon. This knowledge gives you another avenue to limit sensitisation without having to use carbon-free fillers.
For example, you can use the lowest heat setting possible as you weld the tube. You can also avoid making multiple passes of the welding rod over the same area. Multiple passes subject an area to intense heat since the material may not have cooled after the first pass. Avoiding those multiple passes therefore prevents the conditions that favour the formation of chromium carbides at the weld site.
Use of Special Fillers
A third alternative involves selecting filler metals that have special ingredients that prevent the carbon in the filler metal from reacting with the chromium in the stainless steel tube being repaired. For example, niobium and titanium can prevent carbon from reacting with chromium.
However, you need to be careful when using such special filler metals since they can affect other properties, such as toughness and strength, of the stainless steel tubing. Select the special fillers after reading their data sheets and confirming that they will not have an undesirable effect on your stainless steel tubing.
Implement the measures above in order to retain the corrosion resistance of your stainless steel tube after conducting repairs. Ask experts for help in case defects develop despite the precautions that you took to retain the corrosion resistance of the tubing. Those professionals may suggest advanced solutions, such as changing how edges are beveled before welding operations start.
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