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About 90% of the world’s trade is carried by the shipping industry. Ships are also considered important for travel, enjoyment, parties, celebration, defense, military weapon transport etc. The ships are remained for several time-periods in the sea, containing highly salty water and microorganisms. In shipbuilding, the most common metal used is mild steel. Due to highly corrosive nature of seawater, presence of salinity and microorganisms, metals corrode aggressively. Corrosion is the major cause of failure of structure. To protect our material from such deterioration, researchers have developed various methods to protect our precious metal from such disaster like protection through coatings, by using cathodic protection, by using noble metal or corrosion resistant material. Among them, coatings are the most widely used since they are economical and easy to fabricate. There are different types of coatings such as organic and in organic coatings. The aim of this research is to develop such a coating material that will be cheaper and more effective than previously used coatings. In primer election, choice of Zinc Silicate primer is best due to its good adhesion with our substrate mild steel and good resistance to corrosion.
Final coat contains Polyurethane blended with iron oxide particles to increase the corrosion resistance since iron oxide is a stable form of rust; it will resist further corrosion and protect the offshore structure of ship from the corrosion. The corrosion rate of the uncoated sample and coated sample will be analyzed through using different techniques i.e. Tafel Polarization technique and Electro Chemical Impedance Spectroscopy (EIS) in Sodium Chloride (NaCl) solution to analyze the corrosion rate, Salt Spray Test. The corrosion resistance of zinc silicate coated sample was higher than that of uncoated sample and the corrosion resistance of iron oxide blended in polyurethane was much higher than that of uncoated and zinc silicate coated sample. It was clearly shown that the application of coating greatly increased the corrosion resistance of our substrate and protected our sample from corrosion by decreasing the rate to a greater extent.
One of the most important factors for Metallurgical Engineer to be kept in mind while designing a ship and selecting material for its structure is the risk of attack by corrosion. Corrosion is the main reason for ship failure due to which 90 % of the failure is due to corrosion attack. Due to which, the protective elements are consumed after several time period which lead the material to be vulnerable in front of corrosion attack forming unstable oxide layer which lead to the failure of the whole structure. The most dangerous and severe attack of corrosion are faced by ships which are called back after a calculated time-period for maintenance which affects the economy of the shipbuilding industries. The most common steel grade used in shipbuilding as structure due to its strength and economical point of view is mild steel.
We may use stainless steel and other steel grade for better protection from corrosion but that will affect the economy of the industry. For that reason, the corrosion engineers have suggested different solutions to these problems. Like using sacrificial system, using anti-corrosive elements like stainless steel etc and many more, in all of them the most economical factor is the use of anti corrosive coating for the protection of offshore structure from total disaster , increasing the life cycle of the structure and also providing an economical way to protect our structure. Mild steel grade is the most commonly grade of steel used for structure being most economical for them, providing an anti corrosive coating on steel grade for enhancing its life and properties. By using this technique, we can only reduce the corrosion attack and increase its lifetime; because we cannot eliminate the corrosion attack.
Corrosion is an unpleasant word for unpleasant process since it is derived from a Latin word “corrosus” which means eaten away or consumed by degrees. Corrosion is the deterioration of the material as the result of chemical reactions that occurs between our precious material and the surrounding environment. Corrosion is a dangerous disease for our material because it can cause total disaster of our infra structure resulting loss of lives and economics. Corrosion does not occur at the same rate for all elements, if we take example of metals, they corrode differently at different rate depending on various factors. Some pure metals like iron corrode at much faster rate than other like alloys of iron i.e. stainless steel. There is also a small group of metals that rarely corrode that are called noble metals, which include copper, platinum, gold and etc. During the attack of corrosion, metals react with oxygen of atmosphere and are converted into oxides. On the other hand noble metals are the only elements that are found in pure form.
In this world of modern technology, steel has gained quite an importance in the eyes of shipbuilders due to its unique properties such as low cost, re cyclability and excellent mechanical characteristics. However, low corrosion resistance is the main and most important problem of this material. In shipbuilding mild steel is mainly used for offshore structure which is greatly encountered by the marine harsh environments. The effects of corrosion are allegedly responsible for the 30 % of failures on ships and other marine equipments due to high salinity and humidity in marine environment, that’s why marine environment is considered to be highly aggressive. This results in expensive cost to vessel, structure, equipments operation compounded by financial penalties due to breakdown, outages and repair of marine equipments and ships. Marine environment is considered to be highly corrosive in nature itself, which is considered to be main reason for the high corrosion rates. The corrosiveness of the marine environment depends on the topography of shore, wave action at the surface line, temperature, rainfall, prevailing winds and relative humidity.