chapter One

1.0 Introduction

Corrosion is a serious problem in this technologically advanced age. This is the cause of many economic losses and irreversible structural damage. Although it is difficult to estimate the annual cost of corrosion loss for each country, corrosion has been found to be the third largest waste of material resources after war and disease (Olugbenga et al. 2011). Efforts have been made to limit the destructive effects of corrosion through various preventive measures (Loto et al. 1989, Popoola et al. 2011, and Davis et al. 2001). The effects of corrosion in our daily lives are direct, affecting the useful life of our property, and indirect, driving the costs of corrosion to manufacturers and suppliers of goods and services we pass to consumers. there is. At home, corrosion is found on body panels, charcoal grills, patio furniture, and metal tools (Denny et al. 1996). Corrosion of rebar in concrete is usually silent, causing sudden failure of bridges and building sections. Almost all metals corrode to some degree. Fossil-fired boilers and fossil-fired generators experience corrosion problems in components such as steam generators and water walls surrounding the furnace (Natarajanf & Sivan, 2003). Perhaps the most dangerous is the corrosion that occurs in large industrial facilities such as power plants and chemical plants. However, the corrosion consequences are economical and can lead to:

• Replacement of corroded devices.

• Oversized to allow for corrosion.

• Preventive maintenance such as painting.

• Equipment shutdown due to corrosion faults. • Product contamination.

• Reduced Efficiency – For example, when oversize or corrosion products reduce the heat transfer coefficient of a heat exchanger.

• Loss of valuables. B. By corroded containers.

• Otherwise desirable materials cannot be used.

• Damage to equipment other than where corrosion damage occurs. Corrosion affects most of the industrial sector and can cost billions of dollars each year. Therefore, in the modern world, research has been done to overcome this problem by conducting corrosion inhibitor enhancement studies. Corrosion inhibitors slow down either or both the anodization or cathodic reduction. This will give you an anodic, cathodic or mixed escapement. In an effort to find environmentally friendly and readily available corrosion inhibitors, there is a growing trend to use biological substrates such as leaves and plant extracts as corrosion inhibitors for metals in acid washing processes. Increased awareness of environmentally friendly practices for sustainable development has resulted in a significant increase in demand for non-toxic alternatives to toxic inhibitors. In recent years, several plant extracts have been investigated to inhibit acid corrosion of metals. This is because plants contain naturally synthesized compounds that are biodegradable, environmentally safe, inexpensive, readily available and renewable sources of materials.

Corrosion is not only dangerous, it causes billions of dollars in damage each year and is costly. If you don’t believe this, consider some of the direct and indirect effects of corrosion that contribute to these costs.

Not only are the economic costs enormous, but also the potential loss of life and environmental damage can have far-reaching implications for modern industrial enterprises. Therefore, it is essential for operators

1.1 Literature review

Corrosion can be defined as a destructive chemical or electrochemical phenomenon that reacts with the environment to attack any metal or alloy and, in extreme cases, can cause structural failure. Corrosion occurs due to the natural tendency of most metals to return to their natural state (metallurgical reversal). For example, iron reverts to its natural state, iron oxide, in the presence of moist air.

Basically, corrosion can be caused by water ingress and some environmental factors. Water ingress is a major cause of corrosion problems when using equipment in the field. Water can enter the enclosure through free entry, capillary action, or condensation. These three types of water ingress and subsequent water trapping will almost certainly make the enclosure vulnerable to water ingress. At normal atmospheric temperatures, moisture in the air is sufficient to produce corrosive effects. Oxygen is essential for corrosion to occur in water at ambient temperatures. Other factors influencing the corrosion tendency of metals include the acidity or alkalinity of the conducting medium (pH value), the stability of the corrosion products, the organisms (particularly anaerobic bacteria), the various compositions of the corrosive medium, and temperature.

1.2 Corrosion mechanism

Metals do not exist in nature as they react in Freistal. Metals are generally in a high energy state as some energy is added from the ore during the manufacturing process. Ores in lower energy states are more stable than metals in higher energy states. As a result of this difficult thermodynamic struggle, metals have a powerful driving force that releases energy and returns to its original shape. Therefore, under a suitable corrosive environment, the metal reverts to its original state or ore. Electrochemical processes, which are intrinsically involved in corrosion, contrast with extractive metallurgy, which is involved in the production of metals. Corrosion is therefore sometimes considered a reverse process of extractive metallurgy, as shown below.




ir energy cycle

To that extractive metallurgy reverse statement



and others.


According to electrochemistry, the corrosion reaction he can be considered to proceed by two simultaneous reactions.

Oxidation of a metal at the anode (the corroded end that releases electrons) and reduction of the material at the cathode (the protected end that accepts electrons). For the reaction to occur, the following conditions must be met:

• The potentials of the two regions of the structure must be different.

• The areas designated as anode and cathode must be electrically connected together.

• These areas must be exposed to a common electrolyte. • An electrical path is required through or between metals for electrons to flow. Under these conditions, a corrosion cell is formed in which the anode is destroyed by corrosion while the cathode remains inactive. As a result of this process, a current flows through the junction between the cathode and anode. The cathode area is protected from corrosion damage at the expense of metal consumed at the anode. The amount of metal loss is directly proportional to the DC flow. Mild steel loses about 20 pounds per ampere flowing per year. (Thomas, 1994).

Figure 1.1:
Components of an electrochemical corrosion cell

1.3.1 Uniform or thinning corrosion

This form of corrosion attack corrodes the entire surface of the metal and uniformly reduces the thickness of the metal. This occurs in homogeneous metals when there is no potential difference between any points on the surface.

1.3.2 Friction corrosion

Fretting corrosion occurs when two or more parts rub against each other. Scrubbing removes corrosion products and exposes new metal to the electrolyte.

1.3.3 Pitting corrosion

This is the most common type of attack that occurs with dissimilar metals such as steels and other alloys. This is a localized attack where corrosion rates are higher in some places than others. It is caused by potential differences between different points on the metal surface.

1.3.4 Galvanic corrosion

Galvanic corrosion occurs where two dissimilar metals or alloys come into contact. The extent of galvanic corrosion depends on the potential difference between the two metals and the relative sizes of the cathodic and anodic regions.

1.3.5 Intergranular corrosion

Corrosion occurs at the grain boundaries due to the potential difference between the anodic and cathodic grain boundaries. “Sensitized” stainless steels are particularly susceptible to intergranular corrosion, where carbides precipitate at the grain boundaries as a result of improper heat treatment or in the heat-affected zone of the weld seam.

1.3.6 Erosion Corrosion

Erosion is the removal of metal by movement of a fluid against a surface. The combination of erosion and corrosion can corrode at severe rates.

1.3.7 Crevice corrosion

Crevice corrosion occurs when there is a difference in ionic or oxygen concentration between the metal and its surroundings. A lack of oxygen in the electrolyte at the bottom of the sharp V section causes anodic spots to form on the metal, which quickly corrodes.

1.4 Methods of protection against corrosion

1.4.1 Applying protective coatings

Metal structures can be protected against corrosion in a number of ways. A common method is to apply a protective coating of paint, plastic, or precious metal film to the structure itself (eg, tin can coating). These coatings form an impermeable barrier between metals and oxidants, but are effective only if the coating completely covers the structure.

Coating defects have been found to accelerate metal corrosion.

1.4.2 Cathodic protection

Cathodic protection, which uses an applied current derived from an external power source, is a related form of protection in which a metal is forced to become the cathode of an electrochemical cell. For example, most cars now use the negative terminal of the battery as ground. Not only is this process a convenient way to carry electricity, it also shifts the electrical potential of the car chassis, reducing (to some extent) its tendency to rust.


Leave a Comment