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Cleaning Stainless Steel How to clean and protect stainless steel from rust Share this: There is a widespread misconception that stainless steel should not rust; however, oxidation, corrosion, rusting or “staining” of stainless steel is actually quite common. Understanding the Passive Layer When the surface of ordinary carbon steel is exposed to oxygen, it forms ferric oxide (Fe2O3), colloquially known as rust. Ferric oxide doesn’t form a continuous layer on the steel, so it eventually spalls off, leaving raw steel exposed and setting off a destructive rusting cycle. Stainless steel building panels Stainless steel frequently used in architecture because of its unique look and ease of maintenance. Stainless steels undergo a very different process because of their high chromium content. When chromium reacts with oxygen, it creates a passive layer of chromium oxide. Unlike ferric oxide, chromium oxide doesn’t spall off. It acts as a shield, preventing further oxidization of the stainless steel. The passive layer is self-repairing: if it is damaged, chromium in the exposed stainless steel will react with oxygen to form new chromium oxide. As long as there is sufficient chromium present, the chromium oxide layer will continue to reform and protect the stainless steel surface. All stainless steels contain at least 10.5% chromium by weight. The higher the chromium content, the greater the corrosion resistance of the steel. Stainless steel rusting occurs when the passive layer is damaged and does not have a high enough chromium concentration to reform. Causes of Stainless Steel Corrosion Chromium can protect stainless steel if the localized concentration is 12 percent or higher. Anything that reduces the localized chromium concentration below the 12 percent threshold will cause staining or rust. Common causes of stainless steel corrosion include: Chlorides Hydrochloric Acids Sulphuric Acids Contact with Iron Contact with Carbon steel High temperatures Chromium oxide is particularly vulnerable to chlorides. Corrosion is accelerated in coastal areas with salt-spray exposure, and in areas where de-icing salts are used during winter. Components for the chemical and food industries have high chromium content to compensate for regular exposure to chlorine, salt, and other corrosive substances. Strong acids destabilize the passive layer. Exposure to hydrochloric and sulphuric acids causes general surface corrosion. Stainless steel corrosion can also be triggered by contact with iron or carbon steel particles. Trace particles from iron or carbon steel will rust on stainless steel surfaces. If left unattended, rust spots may compromise the chromium oxide surface and, in the worst cases, it can evolve into "pitting," i.e. localized corrosion. Contamination is common when stainless steel is subject to sparks from nearby welding, cutting, drilling, or grinding of carbon steel. A less common form of rusting occurs after the stainless has been exposed to v