Suncor Stainless Product Information Knowledgebase
Search:     Advanced search
Browse by category:
Knowledgebase | Downloads | Glossary | Ask a Question |

Stainless Steel Submerged-Pitting and Crevice Corrosion

Article ID: 47
Last updated: 22 May, 2012
Add comment
Views: 3400
Comments: 0

The chromium portion of the stainless steel must be provided with oxygen to form a protective oxide layer state. The atmosphere normally provides a sufficient amount of oxygen to the stainless steel to maintain this passive oxide layer.When stainless is submerged it may not receive the oxygen that is required for it to remain “passive”(non-corrosive).

Any reduction in oxide protection along the stainless surface causes it to become anodic, or “active”. Meanwhile, the areas surrounding the “active” parts of the metal surface that still contain sufficient oxide protection act cathodic, and remain “passive”. Fresh water or seawater, being the electrolyte provides the path for the ions of the anodic areas to transfer to the surrounding cathodic areas of the metal.
Galvanic attack continues over a period of time until a pit, or many pits form, while the surrounding metal remains virtually corrosion free. Meanwhile, the water inside the cavity-like pits becomes mildly acidic due to the increased concentration of hydrogen and chloride ions, which causes the rate of corrosion to become more aggressive. These pit sizes can range from pinholes to large, shallow depressions.
Crevice corrosion happens in a similar way. Any place where the oxygen is depleted either by dirt or grime, or where there is a seam such as a fastener this can occur.
This article was:  
Add comment
Prev   Next
Benefits of Electropolishing     About Stainless Steel

Others in this category
document Grades of Stainless
document Benefits of Electropolishing
document About Stainless Steel
document Grain Structure
document Corrosion in Stainless Steel