Certified Instrument Specialist (CIS) 2025 Practice Exam – 400 Free Practice Questions to Pass the Exam

The presence of brown stains or rust on metal typically indicates that the metal has been exposed to moisture and oxygen, which leads to oxidation. This process is exacerbated in environments where there is inadequate cleaning or insufficient lubrication. When lubrication is not applied correctly or maintained, it fails to create a protective barrier that shields the metal surface from moisture and contaminants. This situation can allow corrosion to set in, leading to rust formation.

In contrast, excessive lubrication would not result in the development of rust stains, as the extra lubricant would generally provide better protection. Natural weathering might cause surface changes, but these are not typically marked by rust formation unless the metal is not adequately maintained. High-quality materials may have better resistance to corrosion but do not eliminate the need for proper cleaning and lubrication methods. Therefore, insufficient lubricant or improper maintenance is directly responsible for the appearance of brown stains or rust.