Corrosion of Steel and Corrosion Protection...

Corrosion of Steel and Corrosion Protection Corrosion is a multifaceted phenomenon that adversely affects and causes deterioration of properties in metals through oxidation. According to DIN EN ISO 8044 corrosion is defined as ‘Physical interaction between a metal and its environment which results in changes of the metal’s properties and which may lead to significant functional impairment of the metal, the environment or the technical system of which they form a part.’ Steel, the most commonly used material, corrodes in many media including most outdoor environments.  When unalloyed or alloyed steel without corrosion protection is exposed to the atmosphere, the surface takes a reddish brown colour after a short time. This reddish brown colour indicates rust is forming and the steel is corroding. While corroding the steel is getting oxidized to produce rust, which occupies approximately 6 times the volume of the original material consumed in the process. The corrosion process begins when a corrosive medium acts on the steel. The corrosion can be either chemical corrosion or electrochemical corrosion. Corrosion of steel is an electrochemical reaction that requires the presence of water (H2O), oxygen (O2) and ions such as chloride ions (Cl¯), all of which exist in the atmosphere. Atmospheric chloride ions are in greatest abundance anywhere near the coastline. This electrochemical reaction starts when atmospheric oxygen oxidizes iron in the presence of water. In addition, the atmosphere also carries emissions from human activity, such as carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), nitrous oxide (NO2) and many other chemicals, which can also be significant in the corrosion process. The schematics of general corrosion process are illustrated below in Fig 1 Fig 1 Schematics of general corrosion process Types of Corrosion Besides general corrosion, there are various types of localized corrosion...