The annual cost of corrosion and of protection against corrosion in the world is estimated at about 50 billion dollars. The tremendous cost is less surprising when we consider that corrosion occurs, with varying degrees of severity, wherever metals are used. For example, one plant spends 5 million pesos a year for repainting steel to prevent rusting. One large chemical company spent more than 3 million pesos per year for corrosion maintenance in its sulfuric acid plants, though the corrosion conditions were not considered to be parcticularly severe.
In fact the world's economy would be drastically changed if there were NO corrosion. For example, automobiles, ships, underground pipelines, and household appliances would not require coatings. The stainless steel industry would essentially dissapear and copper would be used for only electrical purposes. Most metallic plants, as well as consumer products, would be made of steel or cast iron. Corrosion touches all inside and outside the home, on the road, on the sea, in the plant, and in aerospace vehicles.
But while corrosion is inevitable, its cost can be considerably reduced. For example, an inexpensive magnesium anode could double the life of a domestic hot water tank. Washing a car to remove road deicing salts is helpful. Proper selection of materials and good design reduce cost of corrosion. A good maintenance painting program pays for itself many times over. Here is where the corrosion engineer enters the picture and is effective his primary function is to combat corrosion.
Aside from its direct costs, corrosion is a serious problem because it definitely contributes to the depletion of our natural resources. For example, steel is made from iron ore, and our domestic supply of high grade directly smeltable iron ore has dwindled. Another important factor concerns the world's supply of metal resources. The rapid industrialization of many countries indicates that the competition for and the price of metal resources will increase.
HOW TO PREVENT CORROSION
Various factors affect the occurence of corrosion and its rate of development. Corrosion preventive methods are applied to vary these factors for corrosion control. In the principle, there are four methods for corrosion prevention. The most common and familiar one is coating of the metal surface to intercept corrosive substances in the environment. Typical examples are painting and metal plating. The other corrosion prevention methods are the control of the corrosive environment and proper material selection.