NEBOSH Practice Test

Which failure mode occurs under tensile stress in corrosive environments?

1. Brittle fracture

2. Creep

3. Thermal shock

4. Stress corrosion cracking

The correct answer is: Stress corrosion cracking

When considering the failure mode that occurs under tensile stress in corrosive environments, stress corrosion cracking is the phenomenon that specifically fits these criteria. This type of cracking results from the combined effects of tensile stress and a corrosive environment. In many materials, especially metals, when they are subjected to tensile stresses and are simultaneously exposed to specific corrosive substances (like chlorides), micro-level cracks can initiate and propagate. The presence of corrosion creates an environment where the material becomes more susceptible to cracking, altering how it responds to stress. Unlike brittle fracture, which can occur at lower temperatures and does not necessarily require a corrosive environment, stress corrosion cracking is directly correlated with both tensile stress and corrosive agents. Creep, meanwhile, is a time-dependent deformation process that generally occurs at high temperatures rather than specifically under corrosive conditions. Thermal shock refers to the rapid temperature change that can induce stresses in materials, but again, it is not specifically related to the corrosive environments that are the focus of this question. Thus, stress corrosion cracking is the clearest alignment with the requirement of tensile stress in a corrosive environment, making it the correct choice.