Pitting Corrosion

Pitting corrosion is a localized attack that forms small, deep holes in metal surfaces — often triggered by chlorides, stagnant fluids, or surface flaws. Addressing pitting requires both corrective action and long-term prevention.

How to Repair Pitted Surfaces:

• Surface removal: Grind, blast, or polish the affected area to eliminate corrosion pits and restore uniformity.
• Structural repair: Fill deeper pits using weld overlays or metal-filled epoxies if the damage threatens strength or pressure containment.
• Restore protection: Reapply corrosion-resistant coatings like thin dense chrome, nickel, epoxies, or industrial paints.

How to Prevent Pitting in the Future:

• Select better alloys: Use high-performance stainless steels (e.g., 316, duplex) with strong pitting resistance numbers (PREN).
• Design for drainage: Avoid crevices and stagnant zones where moisture or chemicals can collect.
• Apply protective barriers: Use coatings or chemical inhibitors in corrosive service conditions such as marine or washdown areas.
• Maintain proactively: Rinse away salt or chemical buildup and inspect regularly to catch early signs of damage.

Preventing pitting is critical in components like tanks, heat exchangers, pumps, and stainless steel piping — where hidden localized corrosion can cause sudden failure even when the rest of the surface looks intact. Learn more at our full guide to pitting corrosion.

Pitting corrosion is classified as a wet corrosion process because it requires the presence of an electrolyte — typically water containing aggressive ions like chlorides or sulfates. It forms when a metal’s passive protective film locally breaks down, allowing corrosive agents to attack a small area and create deep pits.

Defining Features of Pitting Corrosion:

• Needs Moisture: It occurs in damp, humid, or submerged environments — especially those with chlorides (e.g., saltwater or cleaning agents).
• Highly Localized: Unlike general corrosion, it focuses attack into tiny, concentrated zones that may not be visible until failure.
• Typical Settings: Common in marine structures, coastal HVAC systems, heat exchangers, and food processing lines.
• Vulnerable Materials: Standard grades like 304 stainless, aluminum, and brass are prone to pitting without the right alloying elements or protection.

Because this form of corrosion relies on moisture and ionic conductivity, it can be minimized by using protective coatings, proper drainage design, chloride mitigation, and selecting pitting-resistant materials like 316 or duplex stainless steels.

Rust is a form of oxidative corrosion that occurs when iron or steel reacts with oxygen and moisture, forming iron oxide. In many cases, it falls under the category of uniform corrosion, where the metal surface corrodes at a relatively consistent rate.

However, under certain conditions — such as uneven moisture exposure, surface contamination, or crevice formation — rusting can become localized. This can lead to pit formation, accelerated thinning in specific areas, or structural weakening that isn’t immediately visible from the outside.

Understanding whether rust is acting uniformly or in isolated spots is key to choosing the right mitigation strategy — from coatings and surface treatments to drainage improvements or material upgrades.