What does the term "running rust" describe?

The term "running rust" specifically refers to corrosion streaks that can appear on painted or unfinished surfaces, often due to moisture interacting with the metal underneath. This form of rust typically presents visually as streaks that run down from a rusting point, creating an aesthetic issue rather than a structural one. It usually indicates superficial rust formation, which may not significantly compromise the integrity of the material but does reflect a need for maintenance to prevent further corrosion.

In this context, while running rust can suggest a potential problem that might evolve into something more serious if left unattended, it remains primarily cosmetic in nature. The surface may look unappealing, but the underlying structural integrity is often intact, which is a key aspect of differentiating running rust from more severe types of corrosion that compromise the strength of the metal.