[1] From a holistic perspective, corrosion is the phenomenon of metals returning to the state they are found in nature.
It is therefore thermodynamically inevitable that these metals when exposed to various environments would revert to their state found in nature.
In the 1990s, Imperial College London even offered a Master of Science degree entitled "The Corrosion of Engineering Materials".
[7] Shreir et al. suggest likewise in their large, two volume work entitled Corrosion.
In 1988 it was estimated that one tonne of metal was converted completely to rust every ninety seconds in the United Kingdom.
Aluminum, galvanized/zinc coatings, brass, and copper do not survive well in very alkaline or very acidic pH environments.
Carbon steels and iron do not survive well in low soil resistivity and high chloride environments.
And nothing survives well in high sulfide and low redox potential environments with corrosive bacteria.
The minimum test of in-situ soil resistivity is measured using the Wenner four pin method if often performed to judge a site's corrosivity.
However, during a dry period, the test may not show actual corrosivity, since underground condensation can leave soil in contact with buried metal surfaces more moist.
Unfortunately, an old dairy farm can have soil resistivities above 3,000 ohm-cm and still contain corrosive ammonia and nitrate levels that corrode copper piping or grounding rods.
Prevention of atmospheric corrosion is typically handled by use of materials selection and coatings specifications.
The same risk from damage and water spray exists for above ground piping and backflow preventers.
Fiberglass covers, cages, and concrete footings have worked well to keep tools at an arm's length.
Drainage from a home's roof valley can fall directly down onto a gas meter causing its piping to corrode at an accelerated rate reaching 50% wall thickness within 4 years.
It is the same effect as a splash zone in the ocean, or in a pool with lot of oxygen and agitation that removes material as it corrodes.
[41] Since chlorides vastly accelerate corrosion, ballast tanks of marine vessels are particularly susceptible.
In January 2018 corrosion of a metal structure caused the emergency closure of Liverpool Lime Street railway station.
With general corrosion it is easier to predict the amount of material that will be lost over time and this can be designed into the engineered structure.
SCC can lead to unexpected sudden and hence catastrophic failure of normally ductile metals under tensile stress.
[55][56] Filiform corrosion is unusual in that it does not weaken or destroy the integrity of the metal but only affects the surface appearance.
[58] Measuring and controlling this is difficult because of the many factors at play including the nature or form of the stress cycle.
[68][69] This phenomenon describes damage to the metal (nearly always iron or steel) at low temperature by diffusible hydrogen.
[85] Also not coupling by welding or other joining method, two dissimilar metals to avoid galvanic corrosion is best practice.
Corrosion in ballast tanks on marine vessels can be an issue if good design is not undertaken.
This is not always the case and should not be used to handle deoxygenated solutions for example, as the stainless steel relies on oxygen to maintain passivation and is also susceptible to crevice corrosion.
[92][93][94][95] One example of controlling the environment to prevent or reduce corrosion is the practice of storing aircraft in deserts.
[96][97] An inhibitor is usually a material added in a small quantity to a particular environment that reduces the rate of corrosion.
[103] As there is more concern for the environment and people are more keen to use Renewable resources, there is ongoing research to modify these materials so they may be used as corrosion inhibitors.
In corrosion prevention applications the purpose of applying the coating is mainly functional rather than decorative.