What Does Non-Uniform Corrosion Mean?
Non-uniform corrosion is corrosion that is non-uniform over the surface. It can be due to inhomogeneities of structure or of composition of the corroding material, or to inhomogeneities of the environment.
This form of corrosion is characterized by significant non-uniform attack such as pitting or crevice corrosion.
Special cases of non-uniform corrosion such as pitting or intergranular corrosion are sometimes called localized corrosion.
Corrosionpedia Explains Non-Uniform Corrosion
Non-uniform corrosion is the destruction of metal that is limited to a localized area and may penetrate deeply into the body of the metal. In this situation, anodic sites do not move around the metal surface but stay in one place. The result is that metal is lost from the fixed location of the anode.
In some cases, solid corrosion byproducts build up in that localized area while a pit forms in the metal underneath.
Non-uniform corrosion can be classified as:
- Spot corrosion.
- Point corrosion.
- Honeycomb corrosion.
- Intergranular corrosion.
- Microbiologically influenced corrosion (MIC).
- Selective corrosion.
Non-uniform corrosion exhibits deep, narrow, isolated corrosion cells that can often cause rapid penetration of the substrate, leading to pinhole leaks that can cause water damage and the possibility of mold growth.
In metal piping, non-uniform corrosion is related to localized changes in water quality and piping which has specific anodic and cathodic sites, and can create completely different corrosion profiles in the same area of the pipe. In concentration cells, micro-environments that drive this corrosion forward also exacerbate dissolved oxygen (DO), creating pipe crevices.
Corrosion byproducts forming over a pit is known as "mounding," and significant mounding leads to tuberculation, which restricts water flow and causes periodic release of metals into the distribution system.