Fundamentals of corrosion: mechanisms, causes, and preventative methods

There are three primary reasons for concern about and study of corrosion: safety, economics, and conservation. Premature failure of bridges or structures due to corrosion can result in human injury or even loss of life. Failure of operating equipment can have the same disastrous results. Several years ago, the National Institute of Standards and Technology (formerly the National Bureau of Standards) estimated that the annual cost of corrosion in the United States was in the range of $9 billion to $90 billion. These figures were confirmed by various technical organizations, including the National Association of Corrosion Engineers. Included in this estimate was corrosion attributed to chemical processes: to corrosion of highways and bridges from de-icing chemicals; to atmospheric corrosion of steel fences; to atmospheric corrosion of various outdoor structures such as buildings, bridges, towers, automobiles, and ships; and innumerable other applications exposed to the atmospheric environment. It has been further estimated that the cost of protection against atmospheric corrosion is approximately 50% of the total cost of all corrosion protection methods. These concerns and studies have been responsible for the development of new alloys and many nonmetallic materials of construction, specifically a wide range of plastic materials of the thermoset and thermoplastic varieties, as well as the development of a wide variety of coatings and linings. When selecting a material of construction for a particular application, that material must have certain physical, mechanical, and corrosion-resistant properties. In the selection process, cost is also an important consideration. Although many alloys may be available to meet the criteria of the application, the cost of these alloys may be prohibitive. As a result, many coating and lining materials have been developed that can be applied to less expensive materials of construction to supply the necessary corrosion protection.