Stainless steel is a steel alloy that contains a minimum chromium content of 10.5%. The chromium reacts with the oxygen in the air and forms a protective layer that makes stainless steel highly resistant to corrosion and rust. At the moment, there are over 150 varieties of stainless steel in the market.
Because of its low maintenance nature, resistance to oxidation and staining, stainless steel is preferred in many applications, particularly those where aesthetics matter.
Even with these impressive features, stainless steel can and does rust after all, it’s 'stainless' not 'stainfree'. Some types of stainless steel are more prone to corrosion than others, depending on the chromium content. The higher the chromium content, the less likely the metal will rust.
But, over time and if not maintained correctly, rust can and will develop on stainless steel.
Various factors can affect the ability of stainless steel to resist corrosion. The composition of the steel is the single biggest concern when it comes to corrosion resistance. The elements in the different grades of stainless steel can have adverse effects on corrosion resistance.
The environment where the metal is used is another factor that can amplify the chances of stainless steel rusting. Environments with chlorine like swimming pools are highly corrosive. Also, environments with salty water can accelerate corrosion on stainless steel.
Finally, maintenance will have an effect on the metals ability to resist rust. The chromium in stainless steel reacts with oxygen in the air to produce a protective chromium oxide layer across the surface. Although very thin, this layer is what protects the metal from corrosion. This layer can be destroyed by harsh environments or mechanical damage such as scratches however, if cleaned properly and in a suitable environment, the protective layer will form again restoring the protective properties.
There are different types of stainless steel corrosion. Each of them presents different challenges and requires different handling.
· General corrosion – it’s the most predictable and easiest to handle. It’s characterised by a uniform loss of the entire surface.
· Galvanic Corrosion – this type of corrosion affects most metal alloys. It refers to a situation where one metal comes into contact with another and causes one or both to react with each other and corrode.
· Pitting corrosion – it’s a localised type of corrosion which leaves cavities or holes. It’s prevalent in environments containing chlorides.
· Crevice corrosion – also localised corrosion that occurs at the crevice between two joining surfaces. It can happen between two metals or a metal and a non-metal.
Rusting stainless steel can be a concern and look unsightly. The metal is designed to resist corrosion which is why most users have fears when they start noticing stains and rusting on the metal. Luckily, there are various methods at different stages that can help to improve rust and corrosion resistance.
Preparation during the planning phase, when using stainless steel, can pay off in the long run. Ensure the metal is used in areas with minimal water penetration to reduce damage to the surface. In cases where contact with water is inevitable, drainage holes should be applied. The design should also allow free circulation of air to prevent damage to the alloy.
During fabrication, exceptional care should be taking on the surrounding environment to avoid cross contamination with other metals. Everything from the tools, storage units, turning rolls and chains should be carefully monitored not to drop impurities into the alloy. This can increase the potential formation of rust.
Once the alloy is installed, regular maintenance is key in rust prevention, also limiting the progression of any rust that might have already formed. Remove formed rust using mechanical or chemical means and clean the alloy with warm water and soap. You should also cover the metal with a rust-resistant coating.
Read more: Density of stainless steel