Can stainless steel rust, or is it truly stainless?

Stainless Steel is a remarkable alloy and can be found in many industries throughout the world. Cornerstone Stainless Containers provides stainless steel equipment used for food, beverage, and pharmaceutical processing, however that is only scratching the surface on the many uses of stainless steel. But is stainless steel truly STAINLESS?

If you compare stainless steel to other metals and alloys, you’ll find that stainless steel offers more corrosion resistance than nearly all other metals. This is because of the components that make up stainless steel, one of which is Chromium. Chromium forms a thin, invisible layer when exposed to oxygen, which is known as Chromium Oxide. This invisible layer is what protects the metallic material from the normal wear and tear cause by an environment/atmosphere containing oxygen.

Below is an example of corrosion on a galvanized steel pipe (6-7 years in a water supply system; TX, USA) compared to a stainless-steel pipe used in a similar fashion.

Stainless Steel clearly offers a much better resistance to the elements, and for the most part is capable of fending off corrosion. But is it truly stainless?

In short, the answer is no, however there is much more to that answer than meets the eye. There are over 150 different grades of stainless steel, all of which have a differing degree of corrosion resistance. In general, the higher the chromium content, the higher the corrosion resistance will be. However, the quality of the product is imperative because any impurities can affect the corrosion resistance.

In addition to the contents of the stainless steel, another factor that can lead to corrosion occurs when the layer of Chromium Oxide is damaged or breaks down. This can be caused by several factors, some of which could be exposure to cleaners, high salinity environments, chloride, high humidity, or mechanical abrasions. More or less, if the stainless steel is in an environment that encourages corrosion, there’s a good chance it will eventually breakdown.

There are ways to combat corrosion even further though! Using a Passivation Process, a manufacturer can create an additional layer of protection.

In stainless steel, the passivation process uses nitric acid or citric acid to remove free iron from the surface. The chemical treatment leads to a protective oxide layer, or passivation film, that is less likely to chemically react with air and cause corrosion. Passivated stainless steel resists rust.

When using a passivated piece of stainless steel, the operator can be confident that corrosion will not be an issue. However, even with this added layer of protection, these barriers can breakdown in certain environments. So, the answer to our question is that stainless steel is never truly stainless, especially in environments that invite corrosion. However, with the proper storage and upkeep, an operator can confidently keep corrosion at bay. Contact CSC