Vapor Phase Corrosion Inhibitor

Painted steel can show rust streaks even when there’s no visible water. The image illustrates rust bleed at a weld/joint—a common result when the steel surface drops below the dew point, trapping condensed moisture (and salts) under the coating. This “flash rust” starts at edges, seams, and welds, then stains the topcoat.

Why it happens

• Dew point condensation: Surface temperature falls below the dew point during prep or application.

• Contamination: Oils, salts, and mill scale left on the surface promote underfilm corrosion.

• Delayed priming: Cleaned steel sits unprotected before coating.

• Edge/weld geometry: Sharp edges and weld spatter are hard to wet out, creating weak spots.

How Carbit helps prevent rust staining

• Dew point control: Verify steel is at least 3–5°F (2–3°C) above dew point during surface prep and coating.

• Clean & decontaminate: Use appropriate cleaners and salt removers; rinse thoroughly.

• Profile & treat welds: Create the specified anchor profile; round edges and treat seams for better wetting.

• Prime the same shift: Apply a corrosion-resistant epoxy or zinc-rich primer promptly, then topcoat with a durable polyurethane or acrylic.

• Protect between steps: Use Carbit Rust Preventives (RPs) for storage and transit; remove per PDS prior to painting to avoid adhesion issues.

Result: Better adhesion, fewer stains, and longer coating life on pipes, valves, and structural steel.

Looking to diagnose rust streaks on existing assets? Carbit can assess conditions on-site and recommend the right cleaners, primers, and topcoats for lasting corrosion protection.