Most common metals and their alloys are attacked by environments such as the atmosphere, soil, water, or aqueous solutions. This destruction of metals and alloys is known as corrosion. It is generally agreed that metals are corroded by an electrochemical mechanism. With practically all commercial processes engineered on a continuous basis of operation, premature failure from corrosion of various types of equipments, including heat exchangers, piping, and others, may mean costly shutdowns and expensive maintenance operations. It is especially troublesome in oil rening, chemical industries, and electric power plants on land and sea, as well as in food and liquor processing, paper manufacture, refrigeration, air-conditioning, etc. Therefore, an understanding of corrosion principles and corrosion control should be of great interest to industry and the general public.