What forms of corrosion can occur on stainless steels?

A plain carbon steel, with negligible corrosion resistance, would suffer from uniform or general corrosion across most of its surface. Although stainless steels are much more resistant to corrosion when compared to ordinary alloy steels, over time corrosion can occur. Within normal water-based environments, stainless steel objects will not corrode easily, as demonstrated by items found within the home (cutlery, saucepans and work-surfaces). Within demanding applications, however, corrosion can take place over a prolonged period. As stainless steels will form a passive protective layer when exposed to oxygen, corrosion will typically only occur when this passive layer becomes damaged or is missing. Therefore, pitting corrosion is the most common form of corrosion that can occur on stainless steels.

Types of Corrosion:

There are multiple different forms of corrosion, depending upon the corrosive environment, component geometry and operating conditions. These include:

• Crevice corrosion – Crevice corrosion occurs in confined spaces to which access of the working fluid from the environment is limited.
• Erosion-corrosion – This is a degradation of a material surface due to mechanical action, often by particles suspended in fast-flowing liquid or gas, bubbles or droplets, impinging liquid, abrasion by a slurry or cavitation.
• Intergranular corrosion – Sometimes known as an intergranular attack (IGA), this type of corrosion is where the boundaries of crystallites of the material will be more susceptible to corrosion than their insides.
• Stress corrosion cracking – This is the growth of crack formation in a corrosive environment which can lead to unexpected sudden failure of normally ductile metal alloys that are subjected to tensile stress (especially at a higher temperature).
• Microbiologically induced corrosion – Microbiologically induced corrosion is the deterioration of metal by processes of corrosion that occur directly or indirectly because of the metabolic activity of microorganisms in cold water systems. This can also result in severe pitting of metals, leading to rapid failures.

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