INTRODUCTION TO CORROSION CHAPTER 1 LECTURER SAHEB M. MAHDI

Definition : Corrosion may be defined in several ways: 1)Destruction or Deterioration of a material because of reaction with its environments. 2)Destruction of materials by means other than straight mechanical. Or 3) it is extractive metallurgy in reverse. Also Corrosion may be defined as the destruction of a metal or an alloy because of chemical or electrochemical reaction with its surrounding environment or medium. Corrosion Engineering Metallurgy in reverse Lcturer SAHEB M.MAHDI

Corrosion damages The serious consequences of the corrosion process have become a problem of worldwide significance. In addition to our everyday encounters with this form of degradation, corrosion causes plant shutdowns, waste of valuable resources, loss or contamination of product, reduction in efficiency, costly maintenance, and expensive over design. It can also jeopardize safety and inhibit technological progress. Corrosion in some cases is desirable, for example chemical machining or chemical milling ( widely used in aircraft and other applications ).Anodizing of aluminum is another beneficial corrosion process used to obtain better and more uniform appearance in addition to a protective corrosion product on the surface. Lcturer SAHEB M.MAHDI

Losses due to Corrosion Lcturer SAHEB M.MAHDI

FIVE GOOD REASONS TO STUDY CORROSION (1) Materials are precious resources of a country. Our material resources of iron, aluminum, copper, chromium, manganese, titanium, etc. are dwindling fast. Some day there will be an acute shortage of these materials. An impending metal crisis does not seem anywhere to be a remote possibility but a reality. There is bound to be a metal crisis and we are getting the signals. To preserve these valuable resources, we need to understand how these resources are destroyed by corrosion and how they must be preserved by applying corrosion protection technology. (2)Engineering knowledge is incomplete without an understanding of corrosion. Aero planes, carriers cannot be designed without any recourse to the corrosion behavior of materials used in these structures. (3) Several engineering disasters, such as crashing of civil and military aircraft, naval and passenger ships, explosion of oil pipelines and oil storage tanks, collapse of bridges and decks and failure of drilling platforms and tanker trucks have been witnessed in recent years. Corrosion has been a very important factor in these disasters. Applying the knowledge of corrosion protection can minimize such disasters. In USA, two million miles of pipe need to be corrosion- protected for safety. Lcturer SAHEB M.MAHDI

(4) The designing of artificial implants for the human body requires a complete understanding of the corrosion science and engineering. Surgical implants must be very corrosion-resistant because of corrosive nature of human blood. (5) Corrosion is a threat to the environment. For instance, water can become contaminated by corrosion products and unsuitable for consumption. Corrosion prevention is integral to stop contamination of air, water and soil. The American Water Works Association needs US$ 325 billion in the next twenty years to upgrade the water distribution system. Lcturer SAHEB M.MAHDI

Cost of Corrosion In all world cost of corrosion is calculated to be in billion dollars/year. This cost involves the cost of material lost and the cost for preventing corrosion. Almost all the metals and alloys would corroded in various environments, some environments are more corrosive than the others. Lcturer SAHEB M.MAHDI

Below are some startling figures of corrosion losses:  The corrosion cost of gas and liquid transmission pipelines in USA exceeds seven billion US dollars. The figure for the major oil producing countries in the Gulf region are not known, however the cost expected to be very high because of highly corrosive environment in the region.  The corrosion-free life of automobiles in the coastal regions of Arabian Gulf is about six months only.  Nearly 95% of concrete damage in the Arabian Gulf coastal region is caused by reinforcement corrosion and consequent spilling of concrete.  It is estimated that 10% of all aircraft maintenance in USA is spent on corrosion remediation.  Major annual corrosion losses to the tune of £350 million in transport, £280 million in marine, £250 million in buildings and construction and £180 million in oil and chemical industries, have been reported in UK. These are uncorrected 1971 figures.  About $120 billion is spent on maintenance of aging and deteriorating infrastructures in USA. Automotive corrosion costs 23.4 billion US dollars annually in USA.  Every new born baby in the world now has an annual corrosion debt of $40. Lcturer SAHEB M.MAHDI

Corrosion Engineering : Is the application of science and art to prevent or control corrosion damage economically and safely. Corrosion engineer : His job is to protect corrosion of various metallic structures, e.g.: corrosion protection of SHIPS, PIPE LINES, INDUSTRIES …etc. Corrosion Engineering is supposed to have the knowledge of Metallurgy, Electro-Chemistry, Mechanical behaviors of Materials, Electrical Engineering, corrosion test, the nature of corrosive environments and the knowledge of Cost analysis. Lcturer SAHEB M.MAHDI

What would be expected from Corrosion Engineer.  Ensuring maximum life of new equipment.  Preservation of existing equipment.  Protecting or improving the quality of a product in order to maintain or improve a competitive position.  Avoiding costly interruptions of production.  Reducing or eliminating losses of valuable products by spillage or leaks.  Refitting of equipment withdrawn from service because of corrosion.  Reducing hazards to life and property that might be associated with corrosion: √ Explosions of pressure vessels or piping systems. √ release of poisonous or explosive gases or vapors. Environments : Practically all environments are corrosive to some degree. Examples are air and moisture. Environment means the condition of corrosion e.g.: Water, Water + Air, Water + Cl 2, Water + H 2 S. Lcturer SAHEB M.MAHDI