Liquid Penetrant Testing Level 1 (PT-1) Practice Exam

Which of the following surface contaminants cannot be removed by cleaning parts in a vapor degreaser?

1. Oil

2. Rust

3. Grease

4. Dirt

The correct answer is: Rust

Vapor degreasing is a cleaning process that utilizes the vapor from a solvent to dissolve and remove surface contaminants. It is particularly effective for substances like oil, grease, and dirt, which can be easily removed due to their soluble nature in organic solvents. Rust, on the other hand, is a form of iron oxide that results from the oxidation of metal. This process creates a stable, adherent layer on the surface of the metal that solvent cleaning is typically unable to dissolve or remove. Additionally, rust often requires more aggressive removal methods, such as mechanical abrasion or chemical treatments specifically designed to remove rust. Therefore, among the listed options, rust is the contaminant that cannot be effectively removed by cleaning parts in a vapor degreaser. This understanding highlights the limitations of vapor degreasing in certain applications, especially when dealing with corrosion products like rust that have different chemical and physical properties compared to oils, greases, or dirt.