Most industries depend upon the efficient and reliable operation of large-scale material handling systems that manufacture, transport and store different chemicals. These systems require huge amounts of forethought, capital, and regular maintenance to function satisfactorily.\u00a0<\/p>\n
As a result, engineering designers do everything in their power to increase longevity while reducing the need for maintenance as far as possible for such systems.<\/p>\n
In this article, we take a look at the process of passivation. Though often overlooked, passivation plays a key role in many large (and small) scale systems to ensure their durability and performance, especially when it comes to stainless steel.<\/p>\n
Passivation is a post-fabrication process that makes a material passive or inert to chemical reactions that can change its composition and ultimately lead to failure. In the industry, the passivation process is typically carried out to make a metal surface more resistant to corrosion or oxidation<\/a> by building a protective film over it.<\/p>\n This thin film, also known as a passivation layer or passivation film, covers the material\u2019s surface but does not make any changes to the base metal. The passive film acts as a barrier to reduce the chemical reactivity of the material making it more resistant to corrosion and contamination. While surface passivation can be done for many ferrous materials<\/a>, it is mostly associated with stainless steels.\u00a0<\/p>\n Stainless steel has self-passivating properties which allow it to form a chromium oxide layer. This layer imparts corrosion-resistant properties. However, when the steel surface undergoes any fabrication processes<\/a>, the metal loses the protective passive film and with it, the corrosion resistance property. The loss of this layer exposes the free iron from underneath and can initiate corrosion. When left unchecked, it can lead to ultimate failure.<\/p>\n Through the passivation process, we can reestablish the protective chromium oxide layer and reduce the concentration of free iron at the surface. The chrome-to-iron ratio must be greater than 1. A ratio of 1.5:1 provides optimum protection from corrosion attacks.<\/p>\n