In regards to metallic materials, we often speak of corrosion. Today, we will focus on its mechanisms, its characteristics and the prevention methods we can implement.
What is general corrosion?
We speak about general corrosion (or uniform corrosion) when all surfarces of a metal (or a large area) are exposed to an aggressive environment. By carefully examining the mechanisms of this type of corrosion, we can observe that it entails both a co-presence and a substantial overlap between:
- anodic area
- cathodic area.
These are not distinguishable between each other. This way, the active metal-environment systems (eg. metals in acidic solutions) are affected as well. In the absence of a protection system, steel exposed to natural environments (e.g. water or soil) corrodes generally.
A distinction: uniform or uneven general corrosion
In addition, general corrosion can be:
- uniform (the same penetration across the surface)
- uneven (penetration has a regular profile).
How to prevent general corrosion?
This type of corrosion is easily monitored and therefore less dangerous. Let’s see together the reasons. It is possible to
- forecast its appearance
- calculate the penetration speed rate.
It is crucial, in fact, to make a careful selection of the material, taking into account the environment where this will work. Only this way it will be possible to calculate its duration in relation to the corrosion phenomenon in a specific time interval. For example: if a stainless steel product comes into contact with oxidizing acids solutions, it can be hypothesized a lifetime, depending on the future replacement of the piece itself.
How to measure general corrosion?
General corrosion can be prevented through a different methods as:
- cathodic protection (it is the electrochemical technique that preserves the metal structures from corrosion that are exposed to an electrolytic environment)
- organic, non-organic and metallic coatings
- paints
- corrosion inhibitors (they are able to temporarily protect the metal).
How can we assess general corrosion?
The resistance to general corrosion may be assessed as:
- excellent (if there is a thickness reduction corrosion less than 0.05 mm/year)
- sufficient (less than 0,50 mm/year)
- scarce (decrease of between 0,50 and 1,27 mm/year)
- very bad (decease more than 1,27 mm/year).
This should be considered when designing your piece. In fact, you must calculate its size in relation to the corrosion rate (with stock allowances or by one of the special methods specified above).
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