Corrosion is the deterioration of materials by chemical interaction with their environment. It is a natural phenomenon requiring three conditions; these are moisture, a metallic surface, and an oxidizing agent such as electron acceptor. A common form of corrosion is rust. The term corrosion is sometimes also applied to the degradation of plastics, concrete, and wood and generally refers to metal. Corrosion does not occur in dry air which is the cause of rusty bolts, corroded part and is theindustrial form of product quality and storage. A certain amount of water vapour has been resent in the air this water vapour or moisture in the air is measured in terms of relative humidity.
In the pure air almost no iron corrosion occurs, at relative humidity,even up to 99% but with contaminant such as sulphure dioxide or solid particles of charcoals present, corrosion couldproceed at relative humidity of 45% or above. However, pure air is seldom encountered in practice. The rate of corrosion is faster where surfaces are exposed to polluted air in combination with high relative humidity. There are two aspects to corrosion prevention and repair. An important factor is that corrosion is irreversible… it always result in a weakened structure while prevention works going forward, repair is the most pressing issue.
Bellow is the causes of corrosion
1. Water, rain moisture.
2. Sea water, salt air.
3. Abrasion and erosion.
4. Chemical, acid, gasses.
5. High velocity flow.
6. Stress, pressure, micro organisms.
7. Age deterioration, electrolysis, electrical imbalance.
The effect of corrosion is dangerous for both humans and other living things,
• Reduce value of goods due to deterioration of appearance.
• Loss of time in the availability of profile making industrial equipment.
• Perforation of vessels and pipes allowing escape of the contents and possible harm t the surroundings
• Mechanical damage to valves, pumps, etc. or blockage of pipes by solid corrosion product.
Corrosion control refers to measures that are implemented on various way of controlling corrosion. In corrosion control application, the controlled space is maintained at a specific relative humidity and temperature so that the product and material in the controlled space cannot absorb moisture from the surrounding atmosphere. Thus the products are also protected from corrosion. Some of the corrosion prevention applications do not have coincidental temperature control. Humidity control is maintained to achieve protection of the area, as this constitutes a much more economical method than air controlling. An example of this is the waste pumping station of sewage plant, where the primary humidity control is the maintenance of dew point within the space which is lower than the temperature of liquid which is being circulated or store there.
There are various ways of controlling corrosion such as;
1. Barrier protection: the concept of a barrier protection is to protect the metal from the environment constituents. Typical forms include anodia oxide, ceramic and inorganic coating, inhibitors and organic coating.
• Cathodic protection (CP): This technology uses direct current to counteract corrosion in structures such as gas pipelines and storage tanks. This helps prevent the onset corrosion and even stop it from worsening.
• Lining and coating: These are substances that, when placed in a certain environment for certain materials such as metal. This can extend the life span of equipment and prevent failures and system shut downs. It can also prevent heat transfer loss and contamination, and preserve the aesthetic appearance of the structures.
• Selection of materials: This refers to choosing materials that are corrosion resistant, such as special alloys, plastic and stainless steel.

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