Q1: Pick out the wrong statement.

ANS:B - Stress corrosion occurs due to the combined action of corrosive environment and the compressive stress.

1. Erosion corrosion: This type of corrosion occurs when the material is subjected to both a corrosive environment and mechanical abrasion or erosion. It often manifests as surface grooves or pits due to the synergistic effects of chemical attack and physical wear. Common examples include the corrosion of piping systems in turbulent flow conditions, where particles or fluid impurities exacerbate material degradation.
2. Stress corrosion: Stress corrosion arises from the simultaneous action of a corrosive environment and tensile stress. Unlike other forms of corrosion, stress corrosion can lead to sudden and catastrophic failure of materials under relatively low applied stresses. It occurs when the material is exposed to specific corrosive environments, such as chloride-rich solutions, while simultaneously experiencing tensile stress. Stress corrosion cracking (SCC) is a common manifestation, where cracks propagate in a direction parallel to the applied stress, leading to structural integrity compromise.
3. Stainless steel and stress corrosion: While stainless steel is known for its corrosion resistance, certain grades, particularly austenitic stainless steels, can be susceptible to stress corrosion in chloride-containing environments. Chloride ions can induce localized corrosion in stainless steel, particularly in the presence of tensile stresses. This phenomenon is often encountered in marine or coastal environments where chlorides are abundant.
4. Direction of crack propagation: In stress corrosion cracking (SCC), the direction of crack propagation typically aligns with the applied tensile stress. This is because the tensile stress promotes the opening of microstructural defects or corrosion pits, facilitating crack initiation and propagation along the grain boundaries or other susceptible sites. Therefore, cracks tend to propagate parallel to the applied stress, rather than perpendicular to it.

In summary, erosion corrosion occurs due to the combined effects of corrosion and mechanical abrasion, stress corrosion arises from the synergy of corrosion and tensile stress, stainless steel can be susceptible to stress corrosion in chloride-rich environments, and crack propagation in stress corrosion cracking tends to align with the applied tensile stress.