Corrosion is a degradation, chemical or electrochemical attack on a metal by it’s surrounding resulting to the formation of an oxide of the metal, salt or other compounds. Corrosion is an oxidation-reduction process. Over the years, corrosion has been a challenging factor to some engineering practices in the world and many studies have been carried out to inhibit the process. Many times, pipelines are located in streamline areas or damp places and the major factor to be considered is the inhibition of corrosion of the pipes, these places maybe acidic or alkaline in nature and the concentration of these components of the environment will contribute to the degradation of the pipes, since most engineering materials are iron and it’s alloys or steel and it’s alloys..
Corrosion study is a vital area of study in the practice of engineering. The study of material and physical metallurgy is essential aspect in this study. This is one of the major trait in engineering materials and constructions.
Types of corrosion
Unlock this exclusive content by using one of the sharing buttons below.There are two general type of corrosion which includes:
- Chemical or dry corrosion
- Electrochemical corrosion
Chemical corrosion: these are corrosion that results due to the chemical reaction between the metal and the components of environment it is found, such components are air, vapor, sulphur and many gases and solutions. It is this type of corrosion that oxidation and reduction is prominent and in this sense. The extent of corrosion Is dependent on the chemical affinity between the corrosive environment and metal.
Metals in group one and two of the periodic table reacts readily with oxygen, therefore beryllium and magnesium which have low specific gravity and good strength can be used in engineering construction. The oxidation of metals such as steel is very low at atmospheric temperature but is high in elevated temperature. Example of this type of corrosion: 2Fe + O2 = 2FeO.
Electrochemical corrosion: this type of corrosion does not occur as in a chemical reaction medium but in an aqueous solution called ‘electrolyte’. The corrosion is brought about the dissociation of the ions in basic reaction. This works in line with the electrolysis of metals though the main aim is nit to produce electric current.
- Pitting corrosion
- Galvanic corrosion
- Erosion corrosion
- Uniform corrosion
- Stress corrosion
- Fretting corrosion
The equipment used to study the influence of PH on corrosion is called the corrosion study kit.
Mechanism of corrosion in electrochemical series
In a conducted experiment to determine the corrosion rate in different buffer solutions, it was discovered that the corrosion taking place in the electrolyte is a reduction in the weight of the mental under study and the color of the solution changed. Electrochemical series is a series of metallic ion that shows the order of preferential discharge in an electrolytic cell. It is arranged from the most reducing agent to the very oxidizing agent which is found at the bottom of the electrochemical series table and these oxidizing agents are below hydrogen
In the explanation of the mechanism of corrosion, the concept of electrochemical series of some metals will be shown in the table below:
|Metallic ion||Electrode potential|
Here hydrogen is used as a reference standard electrode potential as zero.
When the metal is immersed in the electrolyte and left for some time, due to the concentration of the solution, the metal will dissociates into it’s metallic ion and are being deposited in the solution since no cathode is found to exist in the solution. This changes the color of the solution.
Now when an iron material is used in construction, the implication of the corrosion mechanism is that the atmospheric oxygen reacts with the water molecules to form hydroxyl ion ad the hydroxyl ion reacts with iron(ii)ion to form ferric hydroxide which is a reddish brown substance .
Causes of corrosion
Direct contact with water, metal surfaces and air: when a metal is exposed to the atmosphere and it comes in contact with water, an oxidation reduction reaction occurs. This reaction causes corrosion on the metal surface. When a metal with uneven distribution of carbon and other alloys, it tends to corrode easily and fast due to difference in electrical potential with iron as anode and carbon as cathode, this facilitates corrosion.
- Contact with electrolyte
When a metal comes in contact with an electrolyte, a potential difference is set up as a result of difference in concentration level of the involved solution
Temperature affects the rate of oxidation reduction on corrosion process. The increased temperature of the metal increases the kinetic energy of the molecules and this leads number of collision rate.
- Microbial influence
The presence of microbes on a metal can lead to an increased corrosion rate. This is so because the microbes are able to degrade the metals through oxidation reduction.
Others includes: metallurgy, presence of impurity…
In conclusion, the weight loss of the metal is the corroded metal, accounts for the corrosion and it found that corrosion occurs highest in acidic followed by alkaline and water
Prevention of corrosion
There are five basic ways of corrosion control:
- Material selection
- Cathode protection
Importance of corrosion
The economic importance corrosion is based on the good and bad effects of corrosion; here we look out for the economic implication on the nation’s income.
Probably the most aspect of corrosion is on the cost to gives to the nation. The cost of corrosion has been estimated from some industrialized countries and it is found that corrosion has add up to 4% increase in the gross domestic product, this is the case of pipeline purchase and replacement and other equipment that has to do with production.Unlock this exclusive content by using one of the sharing buttons below.
Example is the case of repairs and maintenance of buried pipelines in United Kingdom was estimated to be twenty million Euros as at 1956.
As at 1995, USA spent $296 and $104billions on industrial repairs on corrosion damages.
Material science and engineering by Er. K.R Rajput. First edition, published by S.K. katana and sons in 1999.
Raghavan V.(1990).Material science and engineering. Third edition. Published by prentice hall of India private limited.
CAC Sequerira and A.K.Tiller. microbial corrosion, volume one. Published by Elvsevier science publishers limited.