CORROSION INHIBITION OF ALUMINIUM IN AN ACIDIC MEDIUM
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3.0 Background of Study
Corrosion is an irreversible interfacial reaction of a material (metal, ceramic, or polymer) with its environment that results in the material being consumed or a component of the environment being dissolved into the material. Corrosion can also be defined as the degradation of materials’ properties as a result of interactions with their environments, and corrosion of most metals (and many other materials) is unavoidable. Of the 105 known chemical elements, approximately eighty are metals, and approximately half of these can be alloyed with other metals, giving rise to over 40,000 different alloys. Each alloy will have different physical, chemical, and mechanical properties, but they can all corrode to varying degrees and in different ways . Corrosion eventually leads to the failure of
components and systems in the processing and manufacturing industries, as well as in the service life of many components. Metal and alloy corrosion control is an expensive process, and industries spend vast sums to combat it. We’ve all seen corrosion and know that the process creates a new and less desirable material from the original metal and can result in a component or system losing function. The most common corrosion product is rust, which forms on the surface of steel. 
Figure 1: STAINLESS STEEL RUST
Corrosion is a natural occurrence. When newly manufactured steel is first exposed to air, its initially gleaming surface will rust within a few hours. Metals have a corrosive tendency. related to the low stability of the metallic state. Metals exist in their pure metallic state, with zero oxidation, or in compounds with other elements (in which they acquire positive oxidation states). The chemical reactions that occur during corrosion are reduction-oxidation (redox) reactions. Such reactions necessitate the use of an oxidized (metal) and a reduced species of material (the oxidizing agent). As a result, the entire reaction can be divided into two partial reactions: oxidation and reduction. The metal loses electrons during oxidation. The zone where this occurs is known as the anode. The oxidizing agent gains the electrons shed by the metal during the reduction reaction, and the zone in which this occurs is called the reduction zone.
The cathode is what happens. [3-5]
Corrosion processes alter not only the chemical properties of a metal, but also its physical properties and mechanical behavior. As a result, the effects of corrosion manifest in a variety of ways. The most common type is uniform corrosion, in which the entire exposed surface of the metal is “attacked,” resulting in a more or less uniform reduction in the thickness of the affected metal.
Corrosion processes have an impact on many human activities that use metal products. In general, as levels of economic development rise, so do the costs associated with corrosion. The costs of corrosion of metallic materials are estimated to be $4 billion. percent of the gross domestic product of the developed countries. And this cost, which represents a loss of resources, would be even higher if corrosion protection methods were not so widely used. It is estimated that this protection allows populations to reduce potential losses by a factor of about 30 percent.
1.4Scope of Study
Though the project’s results can be applied in nearly all sectors, the scope of this project has been limited to Corrosion/Corrosion Inhibitors in the oil and gas industry. As a result, corrosion detection and control or reduction techniques have been thoroughly discussed. The project also includes an overview of the various types of corrosion and corrosion inhibition, as well as the terrain in which they occur.
1.5Significance and Benefits of the Study
Corrosion failures can cause personal injuries and fatalities, as well as billions of dollars in costs due to spontaneous shutdown and environmental contamination. As a result, there is a critical need for better methods to monitor the actual deterioration of a component once it is in service in a corrosive environment, analyze that information, and provide a reasonable forecast of the time remaining before maintenance or replacement is required based on decision-making reasoning. The condition of the metals works can always be determined through corrosion inspection and monitoring, and proper corrosion control and maintenance strategies can be implemented.
Many catastrophic incidents caused by corrosion failure had previously been documented.
Every year, corrosion costs the oil and gas industry tens of billions of dollars in lost revenue and treatment costs. The annual total The cost of corrosion in the oil and gas production industry is estimated to be $1.372 billion, divided into $589 million in surface pipeline and facility costs and $320 million in corrosion-related capital expenditures. Corrosion costs US industries an estimated $170 billion per year, with the oil and gas industry bearing more than half of this burden.
1.6 Factors That Influence Corrosion
The nature and extent of corrosion are determined by the metal and the surrounding environment. The following are important factors that may influence the corrosion process:
1.6.1 Primary factors related to metal:
1. The metal’s composition: The corrosion resistance of a metal is determined by its composition. Metals with a lower reduction potential corrode easily, whereas metals with a higher reduction potential do not corrode easily. Reactive metals such as Na, K, Mg, and Zn are more prone to corrosion. Noble metals such as Ag, Au, Pt, and Pd are less prone to corrosion.
2. Metal surface condition: Corrosion is a surface phenomenon; the larger the surface area or finer the grain size of the metal, the more corrosion there will be. A smooth surface is more resistant to corrosion than a rough surface. Due to the rough surface’s ups and downs, a large number of anodic and cathodic air concentration cells will form.
regions. As a result, the metal corrodes.
3. Characteristics of the corrosion product: It greatly influences the rate of corrosion. If the corrosion product is insoluble, stable, uniform, and nonporous, it forms a protective film that prevents further corrosion. Corrosion will continue if the corrosion product is soluble, unstable, porous, and non-uniform.
4. Hydrogen voltage overload: Metal is more prone to corrosion if its hydrogen over voltage is low. When the cathodic reaction is of the hydrogen evolution type with a lower hydrogen overvoltage, hydrogen gas is easily evolved, resulting in a faster cathodic reaction and faster metal corrosion. Cathodic reaction is slow and metal corrosion is slow in metals with higher hydrogen overvoltage.
1.6.2 Related secondary factors environment:
1. The medium’s pH: In general, the lower the pH, the faster corrosion occurs. When the pH is greater than 10, corrosion of iron is greatly reduced due to the formation of a protective coating of iron hydrous oxides. If the pH is between 10 and 3, the presence of oxygen is required for iron corrosion. In the absence of air, severe corrosion occurs if the pH is 3 or lower than 3 due to the continuous evolution of H2 at the cathode. Metals such as Al, Zn, and others, on the other hand, corrode quickly in highly alkaline environments.
2. The temperature: The rate of corrosion increases with increasing temperature. This is due to the fact that increasing the temperature increases the conductance of the aqueous medium. As a result, the rate
The rate of diffusion rises as well.
3. Oxidizing agents present:
The presence of oxidizing agents accelerates metal corrosion. Even noble metals corrode when exposed to oxidizing agents.
4. Relative humidity: The majority of metals corrode faster in humid air than in dry air. Above a certain level of humidity, known as critical humidity, the corrosion rate increases dramatically. Moisture (humidity) provides a conducting medium, which aids in
I Formation of an electrochemical cell on the surface.
(ii) Gas dissolution, such as O2, CO2, SO2, and others, which aids in corrosion.
5. The presence of impurities in the air: The presence of impurities such as SO2, HCl in the environment accelerates corrosion due to the acidic conditions created by their dissolution. For instance, when SO2 is present When sulphuric acid is present in the atmosphere as an impurity, it combines with moisture or rain water to form sulphuric acid. Metals such as iron are more prone to corrosion in the presence of an acid.
The medium’s conductance: The presence of conducting species in the atmosphere accelerates corrosion. This is because the higher the conductivity of the medium, the faster the ions can migrate between the anodic and cathodic regions of the corrosion cell, resulting in faster electron exchange at the electrode surfaces. As a result, the corrosion problem is greater in sea water than in fresh water.
7. The area effect: Smaller the anodic area, larger the cathodic area, faster corrosion; conversely, larger the anodic area, smaller the cathodic area, slower corrosion will be the corrosion rate. This is because electrons liberated at the anode (smaller the anodic area) are quickly consumed by the large cathodic area, increasing the rate of corrosion.
8.Polarization in the anodic and cathodic regions: Polarization of the cathode or anode slows corrosion. If anodic polarization occurs as a result of a reaction, the metal’s tendency to oxidize decreases, and thus metal ion dissolution decreases. This is usually due to an increase in the concentration of ions of dissolved metals in the vicinity of the electrode, but it can also be due to anodic passivity.
Cathode polarization reduces the cathodic reaction, making the combination of cathode reactant and electron more difficult. Both anodic and cathodic corrosion must be maintained for the corrosion to continue. If any one reaction is slower than the rate of corrosion, they should occur simultaneously. The use of depolarizers reduces the polarization effect, increasing the rate of corrosion reaction.
1.4 Types of Corrosion
There are various types of corrosion based on the surrounding environment, material type, chemical reaction, and so on. The following are some general types of corrosion.
1.Corrosion that is uniform
This is also referred to as general corrosion. It is a very common corrosion method. It corrodes the entire surface of the metal and thins it out. On the entire surface, the damage is done at a constant rate. It is easily identified by its appearance. It is controllable, but if not, it destroys the entire metal.
Galvanic Corrosion is a type of corrosion.
This type of corrosion occurs when an electrolyte, such as seawater, is used. Different metals have different electrical potentials. When they are electrically connected and immersed in an electrolyte, the more active metal emerges.
The flow of electric current continues until the potentials between both electrodes are equal. Galvanic corrosion appears at the junction where two non-similar metals meet. The Galvanic Series displays a list of metals from most active to least active (most noble). Galvanic corrosion can thus be controlled by choosing two metals that are close in series. Because platinum is the least active, it is also the least corrosive.
This is caused by random attacks on specific areas of the metal’s surface. This results in large, deep holes. Pits are the name given to these holes. The pit serves as the anode, while the undamaged metal serves as the cathode. It all starts with a chemical breakdown in
the form of a scratch or spot. The pitting process thins out the metal and increases fatigue. It can, for example, be extremely hazardous in gas lines.
This happens when a corrosive environment, such as saltwater, is present. It is caused by cyclic stress and corrosion. Corrosion fatigue occurs when a metal breaks at a stress level less than its tensile strength. The environment in which the metal resides has a strong influence on the initiation and growth rate of cracks. These cracks are too fine to be easily detected. As a result, stress coupons (metal samples) are used to detect corrosion.
It can be caused by the influence of various types of stress, such as applied stresses.
Welding, soldering, cleaning, heating treatment, construction process, casting, and so on are all examples of thermal expansion and contraction. To avoid corrosion fatigue, the materials’ design and construction should be done correctly, by eliminating any stress and environmental factors, as well as crevices.
5. Corrosion between granules
Grains (small crystals) are present in the granular composition of metals and alloys, and their surfaces join together. The grain boundaries are formed as a result of this. As a result, grain boundaries separate the grains. Intergranular corrosion can also be referred to as intercrystalline corrosion. Intergranular corrosion occurs on or near a metal’s grain boundaries. This can be due to welding, stress, heat treatment, or poor service, among other things. Intergranular corrosion can cause the metal to lose strength.
6.Corrosion in Crevices
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