Corrosion of engineering materials especially mild steel poses serious concern to engineers, scientists, researchers and the general public. Corrosion has a huge economic and environmental impact on virtually all facets of the world’s infrastructure, from highways, bridges and buildings to oil and gas, chemical processing and water and wastewater systems. In addition to causing severe damage
and-threats to public safety, corrosion disrupts operations and requires extensive reparis and replacement of failed assets. In the United States, for example, 3.14% of the GDP - equal to $276 billion is lost annually to corrosion (Jaikumar et al., 2010). Corrosion costs world wide are therefore on the order of $U.S. 552 billion. Schmitt (2009) reported that in the United States, the cost of corrosion related to bridges alone amounts to about $8.3 billion per year. In India, corrosion reduces the life or rail to ready half its expected life. The annual loss due to pre-replacement of corroded rail is significant (about Rs. 440 crores) (Jaikumar, 2010). The loss causes by corrosion in Indonesia was estimated at 1-1.5% of GDP. Also the corrosion process of mild steel pipelines in gas and oil field running induced by the presence of carbon dioxide, acid and water has been a serious problem economically and environmentally for decades (Feron. 2008; Booth, 1964).The Thermodynamics of Corrosion
Thermodynamic law slate that a reaction is a strong tendency for high energy state to transform into low energy states; it is also a tendency of metals to recombine with components of the environment that leads to the phonomenon known as corrosion. The pour baix diagram is also known as potentials pH diagram which is basically a graphical electrade potentials as a function of pH the thermodynamic data on reactions between many metals and water have collected and calculated by pourbaix, they have been combined with solability data on oxides and hydroxides and with equilibrium constant for reactions of these to produces pourbaix diagram which indicates thermodynamically stable phases as a function of electrode potential and pH. It is specifies how the stability of different species are affected by potential and pH and hence slow the condition under which a metal will be corroding, immune or passivated.
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