Crevice corrosion is a localized form of corrosion that occurs in narrow crevices or confined spaces on a metal surface, such as those formed between the metal surface and gaskets, flanges, or weld seams. In these areas, the flow of fluids is restricted, causing corrosive substances (such as chlorides) to accumulate and oxygen concentration to decrease, which promotes corrosion.
What Causes Crevice Corrosion?
Crevice corrosion is caused by differences in chemical composition between the interior and exterior of the crevice. In confined spaces, oxygen is consumed more rapidly, leading to lower oxygen concentration inside the crevice compared to the surrounding environment. This creates an electrochemical cell, promoting corrosion in the crevice region.
Which Materials are Susceptible to Crevice Corrosion?
The following materials are more prone to crevice corrosion:
Stainless Steel (especially 304, 316, etc.): Stainless steel is prone to crevice corrosion in chloride environments.
Aluminum Alloys: Aluminum alloys are also susceptible to crevice corrosion, particularly in acidic environments or after mechanical damage.
Titanium Alloys: While titanium alloys have strong corrosion resistance, they can experience crevice corrosion under certain conditions, such as in concentrated chloride environments.
Nickel Alloys: Some nickel-based alloys, such as Hastelloy and Inconel, can also be prone to crevice corrosion under specific conditions.
Which Environments are Likely to Cause Crevice Corrosion?
Crevice corrosion typically occurs in the following environments:
Chloride Environments: Such as seawater, saltwater, and chloride solutions, where chloride ions are the primary cause of crevice corrosion.
Acidic Environments: In low pH environments, metals are more likely to experience crevice corrosion, especially certain types of stainless steel.
Low Oxygen Environments: Any confined space with low oxygen concentration (such as beneath sealing gaskets, flange joints, etc.) can lead to crevice corrosion.
How to Prevent Crevice Corrosion?
Key measures to prevent crevice corrosion include:
Selecting Materials Resistant to Chloride Corrosion: Such as super duplex stainless steel (2205), titanium alloys, Hastelloy, Inconel, etc.
Surface Passivation: Passivating stainless steel and other materials to enhance the stability of the protective film on the surface, reducing the occurrence of crevice corrosion.
Coating Protection: Applying protective coatings, such as polyurethane or epoxy coatings, to effectively prevent corrosive media from coming into contact with the metal surface.
Regular Inspections and Maintenance: Regularly checking the surfaces of equipment, especially in known corrosive environments, to ensure there are no potential crevice corrosion issues.
