• Uniform • Galvanic • Crevice • Filiform • Pitting • Intergranular • MIC • SCC • HB-HE-HIC • Fatigue • Erosion • Stray Current • Index

Different Types of Corrosion
- Recognition, Mechanisms & Prevention

Crevice Corrosion

What is crevice corrosion? Crevice Corrosion refers to the localized attack on a metal surface at, or immediately adjacent to, the gap or crevice between two joining surfaces. The gap or crevice can be formed between two metals or a metal and non-metallic material. Outside the gap or without the gap, both metals are resistant to corrosion.

The damage is normally confined to one metal at localized area within or close to the joining surfaces.

In this photo, a 316 stainless steel tube and tube sheet from a heat exchanger in a desalination plant suffered crevice corrosion due to the presence of crevice (gap) between the tube and tube sheet.

What causes crevice corrosion? Crevice corrosion is initiated by a difference in concentration of some chemical constituents, usually oxygen, which set up an electrochemical concentration cell (differential aeration cell in the case of oxygen).

Outside of the crevice (the cathode), the oxygen content and the pH are higher - but chlorides are lower.

Chlorides concentrate inside the crevice (the anode), worsening the situation. The pH and the oxygen content are lower in the crevice than in the bulk water solution, just as they are inside a pit. Once a crevice has formed, the propagation mechanism for crevice corrosion is the same as for pitting corrosion.

Ferrous ions form ferric chloride and attack the stainless steel rapidly.

• Use welded butt joints instead of riveted or bolted joints in new equipment
• Eliminate crevices in existing lap joints by continuous welding or soldering
• Use solid, non-absorbent gaskets such as Teflon.
• Use higher alloys (ASTM G48) for increased resistance to crevice corrosion

Corrosion and Its Prevention (5-day module)
Corrosion and Its Prevention (2-day module)
Corrosion, Metallurgy, Failure Analysis and Prevention (3 days)
Marine Corrosion, Causes and Prevention (2 days)
Materials Selection and Corrosion (2 days)
Stainless Steels and Alloys: Why They Resist Corrosion and How They Fail (2 days)

Copyright © 1995-2009. All rights reserved.