Corrosion Essay

1240 Words 5 Pages
1 INTRODUCTION Corrosion is a natural process, from which a modified material will either break down into a more basic state or be broken down (Gundiler et al, 2000). The process causes undesirable traits in the product which may range from a change in appearance to failure of structures. The effect of corrosion as addressed by Ahmad (2006) costs many billions to governments, as an outcomeindustry has developed many ways to combat corrosion. Combating corrosion can be done though two methods, by design and by inhibition. This report examines in sections 2 and 3 examples of corrosion control mechanisms from the standpoint of active and then passive responses. The issues of economic alloy, environment and corrosion control combinations are …show more content…
On steel such coatings are generally called sacrificial coatings. They protect the substrate by acting as a sacrificial anode for the steel which is Cathodic to zinc. 2.2 CATHODIC PROTECTION An electrical system for prevention of rust, corrosion, and pitting of metal surfaces which are in contact with water or soil; this creates a concentration cell generating a DC current similar to ahalf-cell an example is shown in Figure 1. FIGURE 1 PIPELINE WITH ANODIC AND CATHODIC REACTIONS ( AHMAD, 2006) 2.3 CONVERSION COATING Conversion coatings as described in Engineering Fundamentals (2009) are coatings for metals where the metallic surface is converted by the coating with a chemical or electro-chemical process. Examples include chromate conversion coatings, phosphate conversion coatings, bluing, black oxide coatings on steel, and anodizing. They are used for corrosion protection, increased surface hardness, and as paint primers. Conversion coatings are usually built up on aluminium alloys, either by anodizing or chromate conversion. 2.4 BARRIER COATING To exclude liquids, chemicals, humidity (Figure 2) or oxygen from the steel surface an inorganic or organic material can be used to cover the metallic surface (Myles, 1995). This is the most widely used method of protection against corrosion. The inorganic materials can be metals and vitreous enamels. The organic materials can be paints, bitumen products or

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