Unlike carbon steel, stainless steel will not readily corrode, rust or stain from water contact and moisture. Stainless steel is also known as inox steel, derived from the French word “inoxydable“.
The strength and durability of stainless steel makes it a desirable yet expensive option. Due to its expense it is normally used in products where both the strength of steel and corrosion resistance are required. So we see stainless steel used in products like kitchen sinks, cooking vats or rainwater tanks.
The main difference between stainless steel and carbon steel is the amount of chromium present. Chromium is a chemical element that is a hard, steely-gray and lustrous metal. It protects stainless steel by forming a chromium oxide layer. This layer provides a protective shell that blocks oxygen seeping into the metal’s internal structure which would cause corrosion.
Stainless steel generally contains between 12-30% of chromium. Chromium protects stainless steel as long the localised concentration is in excess of 12%. If the stainless surface is contaminated by other metals or chemicals like chlorine, then the localised concentration of chromium can fall below 12%. This then results in the chromium oxide barrier failing and what is known as “pitting” to occur.
Pitting is a localised form of corrosion that can lead to small holes or “pits” in the stainless metal. It is therefore important to regularly clean stainless steel products and equipment with fresh water. If you notice rust spots occurring on your stainless steel product, then remove the rust spots and clean as soon as possible to prevent irreversible pitting.
While stainless steel is obviously durable, it is only strong as the rainwater tank that is built. Some who buy them end up with leaks at due to corrosion of the joints, rivets or screws due to inferior metals being used. These obviously have the potential to be the source of corrosion and leakage. An investigation by the Public and Environment Health Services in Tasmania found water in some stainless steel tanks containing harmful levels of lead. So it is important to take care when selecting a stainless steel tank.