There are many technical questions that arrive every day on our blog. Today we want to share with you a really interesting request.
Technical question: stainless steel and soil composition!
One of our readers asked us how many years a 1mm-thick stainless steel sheet can last underground.
Let’s see how our expert Alessandro answered this question analyzing the soil composition.
Answer of our expert.
In order to be able to answer this question correctly, a number of preventive considerations need to be made. First, it is necessary to know what type of stainless steel is being considered and then we need to know the composition of the soil (or at least what contaminants may be contained in it).
For example, if we’re on the coast, we can have a sodium chloride-rich soil. And even a soil near roads treated with defrosting salts could have the same content. In these cases, therefore, it would be appropriate to use AISI 316/A4 stainless steel, containing molybdenum, ideal for resisting oxidation in this type of saline environment.
Agricultural land, for example, may contain acids or, near swimming pools or aqueducts, they can also absorbed significant amounts of hydrochloric acid. In these cases, however, the stainless steel described above may not be enough and you should opt for a Duplex steel. The latter, in fact, has a ferritic-austenitic structure that offers greater guarantees, both as resistance to corrosion, and as mechanical resistance.
If the soil hasn’t special components, and isn’t subjected to significant chemical attacks, a simple AISI 304/A2 may be sufficient. In addition to this, it is necessary to assess what kind of mechanical stresses the sheet will be subjected to. Sometimes, in fact, there are tensions that can remove the passive layer and make possible aggression by external agents.
In this soil, it is also necessary to be careful of the presence of other metals that could trigger a process of galvanic corrosion. It is possible, in fact, that the absence of oxygen does not regenerate the layer of oxides that covers the stainless steel, in case of accidental removal (e.g. scratches while laying, etc..).
Finally, a sheet with a porous surface doesn’t help to defend against corrosion.
So, in conclusion.
It becomes difficult to determine exactly how long a stainless steel sheet can last underground, given also the influence of the many factors mentioned above.
Beware of those who guarantee stainless steel for a certain number of years. The stainless steel preservation often depends more on the external environment in which it is placed and on proper maintenance, than on its quality.
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