Corrosion Engineering Quiz: How Well Do You Know Corrosion Engineering?

The main cause for the IGC attack in SS is the formation of chromium carbide precipitate at the grain boundary. This is because the chromium carbide precipitate depletes the chromium content in the grain boundary region, making it susceptible to corrosion. The depletion of chromium reduces the protective passive film on the stainless steel, leading to intergranular corrosion.

Passivity in stainless steel is due to the formation of an oxide film. This oxide film acts as a protective layer, preventing further corrosion of the steel by acting as a barrier between the metal and the surrounding environment. This film is formed naturally on the surface of stainless steel when it is exposed to oxygen, and it helps to maintain the stainless steel's corrosion resistance properties.

Rusting of iron involves a chemical reaction between iron, water, and oxygen. This reaction leads to the formation of iron oxide, which is the reddish-brown substance commonly known as rust. This process is an example of electrochemical corrosion because it involves both chemical reactions and the transfer of electrons between the iron and the surrounding environment.

Aluminum can be used for cathodic protection of steel because it is more reactive than steel. When aluminum is in contact with steel, it acts as a sacrificial anode and corrodes instead of the steel. This process helps to protect the steel from corrosion by diverting the flow of electrons and preventing the oxidation of the steel.

Anodic metallic coating refers to a process in which a metal coating is applied to a substrate to protect it from corrosion. In this case, the typical example of anodic metallic coating is Zn on Steel, which means that zinc is applied as a protective layer on steel. Zinc is commonly used as a sacrificial coating because it has a higher electrochemical potential than steel, meaning it will corrode before the steel does, thus protecting it from rusting. Therefore, Zn on Steel is a suitable example of anodic metallic coating.

A Pourbaix diagram is a graphical plot that shows the stability of different chemical species in a solution as a function of both the pH (acidity or alkalinity) and the electrode potential (E). It provides information about the conditions under which a particular chemical species can exist and be stable. By plotting E (electrode potential) on the y-axis and pH on the x-axis, the Pourbaix diagram shows the regions where different species are stable, such as metal oxides, hydroxides, or sulfides. This information is important in understanding corrosion, electrochemical reactions, and the behavior of different materials in various environments.

In a zinc-aluminium galvanic couple, when exposed to acidic solutions, zinc dissolves. This is because zinc is more reactive than aluminium and is therefore more susceptible to corrosion in acidic environments. The acidic solution provides the necessary conditions for the zinc to undergo a chemical reaction and dissolve, while the aluminium is less affected and does not dissolve to the same extent.

The tip and morphology of the crack due to SCC phenomenon will be sharp and transgranular. This means that the crack will have a sharp, well-defined tip and will propagate through the grain boundaries of the material. This is characteristic of stress corrosion cracking, where the combination of tensile stress and a corrosive environment leads to crack initiation and propagation along the grain boundaries.

The correct answer is Galvanic cell. Galvanic cells are electrochemical cells that generate electrical energy from the chemical reactions occurring between two different metals or metal ions. In this case, the iron pipe and the copper are in contact with each other, forming a galvanic cell. The iron pipe is more anodic, meaning it is more likely to undergo oxidation and lose electrons, while the copper is more cathodic, meaning it is more likely to undergo reduction and gain electrons. This creates a potential difference between the two metals, resulting in the generation of electrical energy.

The equation for uniform corrosion is given by mpy = 534/(DAT). This equation represents the rate of corrosion, measured in mils per year (mpy), which is equal to 534 divided by the product of the density (D), the atomic weight (A), and the time (T) in years. This equation is used to calculate the rate of uniform corrosion in various materials and can be helpful in determining the expected lifespan or degradation of a material due to corrosion.

Knife line attack in IGC refers to the corrosion that occurs in the high temperature heat-affected zone (HAZ) of a welded joint. This type of corrosion is typically seen in stainless steel and other alloys that are susceptible to intergranular corrosion. The high temperature HAZ is the region of the metal that experiences the most significant changes in microstructure and mechanical properties due to the welding process. This makes it more vulnerable to corrosion, especially in environments with high chloride content. Knife line attack is characterized by a distinct line of corrosion along the grain boundaries in this zone.

In stress corrosion cracking, the application of ultimate tensile stress can lead to the initiation and propagation of cracks in a material when it is exposed to a corrosive environment. However, if the stress applied is at 100% of the material's ultimate tensile stress, the likelihood of stress corrosion cracking is higher. Therefore, to minimize the risk of stress corrosion cracking, the experimental setup should involve the application of a stress level that is less than 100% of the material's ultimate tensile stress.

The pitting factor of unity represents uniform corrosion. This means that the rate of corrosion is equal across the entire surface, resulting in a consistent and even degradation of the material.

The sensitization caused in stainless steel for IGC to occur is the prerequisite before exposure to corrosive medium. This means that before the stainless steel is exposed to a corrosive medium, it needs to undergo sensitization in order for intergranular corrosion (IGC) to occur. Sensitization refers to the formation of chromium carbides at the grain boundaries of stainless steel, which can lead to the loss of corrosion resistance.

When a non-metallic material forms a crevice on a metallic surface, it is known as a gasket. A gasket is a mechanical seal that fills the space between two or more mating surfaces, usually to prevent leakage from or into the joined objects while under compression. In this case, the non-metallic material creates a crevice or gap on the metallic surface, which is typical of a gasket's function.

The Pilling-Bedworth ratio is a measure of the stoichiometric relationship between the amount of metal consumed and the amount of oxide formed during oxidation. It is specifically relevant to high temperature oxidation, where metals react with oxygen at elevated temperatures. The ratio helps determine whether the oxide layer formed during oxidation is protective or not. A Pilling-Bedworth ratio greater than 1 indicates that the oxide layer is non-protective, while a ratio less than 1 suggests a protective oxide layer. Therefore, the Pilling-Bedworth ratio is most pertinent to high temperature oxidation.

The correct answer is "fogging." Fogging refers to the uniform corrosion of nickel and nickel base alloys. This type of corrosion occurs when the surface of the metal becomes covered in a hazy or foggy appearance due to the formation of a thin layer of corrosion products. Tarnishing refers to the discoloration or dulling of a metal's surface, while dulling refers to the loss of shine or luster. None of these terms accurately describe the specific type of corrosion observed in nickel and nickel base alloys.

The formation of a horse-shoe pit is a characteristic feature of erosion corrosion. Erosion corrosion occurs when a metal surface is exposed to a high-velocity fluid or abrasive environment, causing the metal to wear away and create pits or grooves. The shape of a horse-shoe pit is typically formed by the fluid flow patterns, which concentrate the erosion in a specific area. This type of corrosion is commonly observed in industries such as oil and gas, where the flow of fluids can be turbulent and corrosive.

Fretting corrosion refers to the damage caused by repeated small-scale sliding or rubbing motion between two surfaces in contact. In the context of railroads, this phenomenon can occur due to the constant vibration and movement of the train wheels on the tracks. The repeated rubbing and sliding motion can lead to the formation of corrosion and wear on the rail surface, potentially compromising its integrity and safety. Therefore, fretting corrosion is a plausible explanation for the corrosion that occurs on railroads.

Catastrophic oxidation is exhibited by metals obeying linear rate law kinetics. This means that the rate of oxidation is directly proportional to the concentration of the oxidizing agent. In other words, as the concentration of the oxidizing agent increases, the rate of oxidation also increases in a linear fashion. This type of kinetics is characteristic of metals undergoing rapid and severe oxidation reactions, leading to catastrophic failure.