Stainless Steel and Corrosion Protection

Steel is the most utilised material for construction. Made from an unnatural form of iron, environmental factors can cause steel to revert back to its natural oxide which is better known as corrosion.

Corrosion protection is thus an integral part of the steel fabrication process in order to combat the corroding forces of nature and to maintain the integrity of any steel structures.

When it comes to corrosion protection considerations stainless steel is often the best steel of choice for highly aggressive and corrosive conditions due to stainless steels greater resistance to corrosion.

Passivity is a built-in mechanism which stainless steels possess to combat corrosion. A chromium content of more than 11% gives stainless steel this passivity due to the formation of a very thin but uniform chromium-rich oxide film on the surface of the steel.

Increasing the chromium content and also by adding other elements such as molybdenum and nitrogen the passivity can be improved which would extend the use of stainless steels to even more corrosive applications.

The key to the corrosion protection of stainless steel is to maintain the integrity of the passive layer, which if damaged or removed, should be allowed to repair itself.

The passive film will generally re-form spontaneously but not necessarily instantaneously in an oxygen rich environment, provided that the surface of the steel has been properly cleaned or descaled. Scales are not only undesirable for aesthetic reasons but they also result in a reduced corrosion protection of the underlying stainless steel surface layer. Any contamination or thermal discolouration should also be removed in order for passivation to take place.

To generate a more rapid and complete passivity by removing ferrous contamination and high-temperature scales resulting from welding or other high-temperature operations, stainless steel can be treated chemically by pickling with a mild oxidant such as a nitric acid solution or a mixed acid solution of nitric and hydrofluoric acid. Chemical passivation will enhance the spontaneous formation of the protective passive film.

Thermal contamination on stainless steel can be removed mechanically by grinding or polishing and also by chemical pickling.

Steelmor is the leading supplier and manufacturer of stainless steel in South Africa and is dedicated to supplying cost effective quality products on time. Give us a call to find out how we can help you with your stainless steel requirements.

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