Corrosion is a natural process
Materials corrode due to the deterioration caused by its interaction with its environment. It is the process in which metallic atoms form compound in the presence of water and gases. (Machinery’s Handbook 29th edition, “Corrosion is an irreversible interracial reaction of a material (metal, 2013) ceramic, polymer) with its environment which results in its consumption or dissolution into the material of a component of the environment.
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Often, but not necessarily, corrosion results in effects detrimental to the usage of the material considered.
Exclusively physical or mechanical processes such as melting and evaporation, abrasion or mechanical fracture are not included in the term corrosion. “( Advances in Corrosion Engineering Lecture 1, 2013) Corrosion and erosion is two different things. Corrosion can’t be caused by physical causes unlike erosion, galling or wear. Chemical attack accompanies physical deterioration as described by the terms: corrosion erosion, corrosive wear, fretting corrosion. Plastics may swell or crack , wood may split or decay, granite may erode, Portland cement may leach away.
But the term corrosion is presently restricted to chemical attack of metals. Rusting is only applied to the corrosion of iron or iron base alloys with formation of corrosion products consisting largely of hydrous ferric oxides. Nonferrous metals, therefore, corrode but do not rust. (Corrosion and Corrosion control, 2013) There are three significant reasons of studying corrosion. The first area of significance is economic which includes the objective of reducing material losses resulting from the corrosion of piping, tanks, metal components of machines, ships, bridges, marine structures and so on.
The second area is improved safety of operating equipment which may be hindered by corrosion and will lead to dictatorship consequences. The last significance is conservation, applied primarily to metal resources which is limited in this world, and the wastage of them includes corresponding losses of energy and water reserves associated with the production and fabrication of metal structures. The least important reason is the accompanying conservation of human effort entering the design and rebuilding of corroded metal equipment, otherwise available for socially useful purposes. Corrosion and Corrosion There are five facts in the process of corrosion formation. First, ions are involved and need a medium to move in (usually water). Second, oxygen is involved and needs to be supplied.
Third, the metal has to be willing to give up electrons to start the process. Fourth, A new material is formed and this may react again or could be protective of the original metal . Fifth, A series of simple steps are involved and a driving force is needed to achieve them. The most important fact is that interfering with the steps allows the corrosion reaction to be stopped or slowed to a manageable rate. Beginners Guide to Corrosion , 2003) There are two basic types of corrosion namely uniform and localized corrosion. Uniform corrosion occurs veer the majority of the surface of a metal at a steady and often predictable rate. Although it is unsightly its predictability facilitates easy control, the most basic method being to make the material thick enough to function for the lifetime of the component. Localized corrosion can deal a more severe damage than uniform surprisingly short period of use or exposure.
There are thirteen types of localized corrosion namely galvanic corrosion, pitting corrosion, selective attack, stray current corrosion, microbial corrosion, intracellular corrosion, concentration cell corrosion, harmonically corrosion, corrosion caused by combined action, corrosion fatigue, fretting corrosion, stress corrosion cracking, and hydrogen damage. (Beginners Guide Cost of corrosion and its control experienced by one pulp to Corrosion, 2003) and paper company was estimated to be 20 million dollars annually.
The United States alone have total combined losses of corrosion estimated conservatively to be about 70 billion dollars annually, or 4. 2% of the gross national product . It has been estimated that about 15% of this total could be avoided if currently available corrosion technology were effectively applied. Studies of the cost of corrosion to Australia, Great Britain, Japan, and other countries have also been carried out. In each country studied, the cost of corrosion is approximately 3-4% of the GNP. Corrosion and Corrosion Control, 2013) Indirect losses are more difficult to assess, but a brief survey of typical losses of this kind compels the conclusion that they also cost several billion of dollars. Indirect losses are divided into five which are shutdown, loss of product, loss of efficiency, contamination of product, overdressing. The shutdown of corroded equipments can cost a lot while repairs is underway. Loss of products occur through corroded pipe systems until repairs are made.