Corrosion is the deterioration of a metal as a result of chemical reactions between it and the surrounding environment. Both the type of metal and the environmental conditions, particularly what gases that are in contact with the metal, determine the form and rate of deterioration.
The most common example of corrosion is, of course, rust. The reddish-brown compound referred to as rust is actually iron oxide (Fe2O3), a result of reactions between oxygen and iron. But the oxidization of iron is just one example of corrosion. Corrosion can take many forms, which are classified depending on the environmental causes. More... Corrosion Prevention
The World Corrosion Organization estimates the global cost of corrosion to be roughly US$ 2.2 trillion annually, and that a large portion of this - as much as 25% - could be eliminated by applying simple, well-understood prevention techniques. Corrosion prevention should not, however, be considered solely a financial issue, but also one of health and safety, as evidenced by the 1967 collapse of Silver Bridge. An effective prevention system begins in the design stage with a proper understanding of the environmental conditions and metal properties In virtually all situations, metal corrosion can be managed, slowed or even stopped by using the proper techniques. Corrosion prevention can take a number of forms depending on the circumstances of the metal being corroded. Corrosion prevention techniques can be generally classified into 6 groups: 1. Environmental Modifications
2. Metal Selection and Surface Conditions
3. Cathodic Protection
4. Corrosion Inhibitors
Corrosion is caused through chemical interactions between metal and gases in the surrounding environment. By removing the metal from, or changing, the type of environment, metal deterioration can be immediately reduced. This may be as simple as limiting contact with rain or seawater by storing metal materials indoors, or could be in the form of direct manipulation of the environmental affecting the metal. Methods to reduce the sulfur, chloride or oxygen content in the surrounding environment can limit the speed of metal corrosion. For example, feed water for water boilers can be treated with softeners or other chemical media to adjust the hardness, alkalinity or oxygen content in order to reduce corrosion on the interior of the unit. Metal Selection and Surface Conditions:
No metal is immune to corrosion in all environments, but through monitoring and understanding the environmental conditions that are the cause of corrosion, changes to the type of metal being used can also lead to significant reductions in corrosion. Metal corrosion resistance data can be used in combination with information on the environmental conditions to make decisions regarding the suitability of each metal. The development of new alloys, designed to protect against corrosion in specific environments are constantly under production. Hastelloy® nickel alloys, Nirosta® steels and Timetal® titanium alloys are all examples of alloys designed for corrosion prevention. Monitoring of surface conditions is also critical in protecting against metal deterioration from corrosion. Cracks, crevices or asperous surfaces, whether a result of operational requirements, wear and tear or manufacturing flaws, all can result in greater rates of corrosion. Proper monitoring and the elimination of unnecessarily vulnerable surface conditions, along with taking steps to ensure that systems are designed to avoid reactive metal combinations and that corrosive agents are not used in the cleaning or maintenance of metal parts are all also part of effective corrosion reduction program. Cathodic Protection:
Galvanic corrosion occurs when two different metals are situated together in a corrosive electrolyte. This a common problem for metals submerged together in seawater, but can also occur when two dissimilar...
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