Introduction to Corrosion
– Corrosion is a natural process that converts refined metal into a more stable oxide.
– It is the gradual deterioration of materials by chemical or electrochemical reaction with the environment.
– Corrosion engineering is dedicated to controlling and preventing corrosion.
– The most common type of corrosion is electrochemical oxidation of metal in reaction with an oxidant.
– Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion.
Types and Effects of Corrosion
– Corrosion can occur in materials other than metals, such as ceramics or polymers.
– Degradation is a more common term used for corrosion in non-metal materials.
– Corrosion degrades the useful properties of materials and structures.
– It affects mechanical strength, appearance, and permeability to liquids and gases.
– Corrosion can be localized, forming pits or cracks, or it can be uniform across a wide area.
Specific Types of Corrosion
– Galvanic corrosion occurs when two different metals have physical or electrical contact in a common electrolyte.
– Corrosion removal methods, such as using phosphoric acid or rust removal products, can be used to remove corrosion products.
– Resistance to corrosion can be achieved through methods like painting, galvanization, and cathodic protection.
– Passivation is useful in mitigating corrosion damage, but breakdown of the passive film can lead to pitting corrosion, crevice corrosion, and stress corrosion cracking.
– Pitting corrosion occurs when corrosion pits form and continue to grow even under normal conditions.
– Weld decay and knifeline attack are specific types of corrosion that can occur in stainless steel.
– Crevice corrosion occurs in confined spaces with limited access to the working fluid.
– Hydrogen grooving is the corrosion of piping at grooves created by corrosive agents and hydrogen gas bubbles.
– High-temperature corrosion occurs when a metal is exposed to a hot atmosphere containing oxidizing compounds.
– Aerobic corrosion, biogenic sulfide corrosion, concentration cells, and accelerated low-water corrosion are other types of corrosion.
Protection from Corrosion
– Various treatments are used to slow corrosion damage to metallic objects, including proper treatment of metallic alloys and shrink-wrapping equipment.
– Surface treatments like plating, painting, and enamel application can be used for anti-corrosion purposes.
– Controlled permeability formwork (CPF) enhances the durability of concrete cover to prevent corrosion of reinforcement.
– Sacrificial anodes made of aluminum, zinc, magnesium, and related alloys can be used to inhibit corrosion.
– Impressed Current Cathodic Protection (ICCP) systems, which use specialized anodes connected to a DC power source, provide more precise protection compared to sacrificial anodes.
– Anodic protection impresses anodic current on the structure to be protected and is used for metals that exhibit passivity.
– The rate of corrosion can be measured using various methods, including the weight loss method and instruments based on the half-cell potential.
Economic Impact of Corrosion
– The total annual cost of corrosion in the United States is estimated to be over $1 trillion.
– Corrosion can lead to the deterioration of infrastructure, increased maintenance and repair costs, and loss of productivity.
– Industries such as oil and gas, transportation, and construction are particularly affected by corrosion.
– Implementing effective corrosion prevention and control measures can significantly reduce economic losses. Source: https://en.wikipedia.org/wiki/Corrosion
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Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen, hydrogen or hydroxide. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal and results in a distinctive orange coloration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including mechanical strength, appearance, and permeability to liquids and gases.
Many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area, more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.
The chemistry of corrosion is complex; it can be considered an electrochemical phenomenon. During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves as an anode. The electrons released at this anodic spot move through the metal to another spot on the object, and reduce oxygen at that spot in presence of H+ (which is believed to be available from carbonic acid (H2CO3) formed due to dissolution of carbon dioxide from air into water in moist air condition of atmosphere. Hydrogen ion in water may also be available due to dissolution of other acidic oxides from the atmosphere). This spot behaves as a cathode.
