The resistance of stainless steel to the phenomenon of corrosion

Stainless steel resistance

Inoxstyle is committed to making outdoor showers that can withstand the elements. Both the single body design and the materials are therefore chosen and studied to ensure maximum efficiency in terms of aesthetics and use.

In questo articolo, trattiamo il tema della corrosione e i motivi per cui l’acciaio inox sia resistente a questo fenomeno.

Why does corrosion occur in metals?

All metals – with the exception of noble metals such as gold and platinum – which are found in their natural state, are always extracted from their ores. Metals therefore have a tendency to remain in a stable state (their original state), which corresponds to the oxide state.

Metal corrosion is essentially an electrochemical reaction that takes place at the interface between metal and the surrounding environment.
It is always uncertain to be able to predict, in general, the behavior over time of a certain metallic material if placed in contact with a certain environment.

The parameters that favor corrosive phenomena are:

  • the concentration of the aggressive agent;
  • the temperature of the aggressive agent;
  • the velocity of fluid on the walls of the material;
  • the surface finish of the metal.

Types of corrosion

  • Punctual Corrosion: localized breakage of the passivated layer of stainless steel caused by an electrolyte rich in chlorides or sulphides.
  • Cavernous corrosion: in an electrolyte with a high percentage of chlorides, a closed area of a product built with a bad design, favors the accumulation of chloride ions. The progressive acidification of the environment destabilizes the passivated layer.
  • Intergranular Corrosion: type of corrosion that can occur in the welded areas that appear as “depleted” due to the progressive corrosion that affects the chromium.
  • Stress corrosion cracking: this type of corrosion affects the entire surface of the component, attacked by a corrosive element. On a micro-graphic scale, it corresponds to a uniform loss of thickness and weight.

The corrosive action of salt water environments

The composition of sea water and its physical and chemical properties are constant almost all over the world, with few but decidedly significant local variations. Of great importance for the phenomenon of corrosion are:

  • the amount of dissolved oxygen;
  • the pH;
  • the temperature;
  • the turbulence;
  • the activity of microorganisms;
  • the balance between carbonates and bicarbonates;

In sea water (at temperatures below 30-40°C) the presence of bacterial activity leads to the formation on the surface of a film made up of biological substances, the so-called biofilm, which catalyzes the reduction of oxygen and increases the risk of corrosion from chlorides.

Stainless steels, thanks to their chemical composition, have the ability to self-passivate and to be able to cope with the most diverse conditions of aggression. Let’s see this aspect in more detail.

Why does stainless steel resist corrosion?

In general, the best behavior against corrosive phenomena is offered by austenitic steels, which have a particularly resistant passive film. This film is made up of chromium and molybdenum oxides, elements resistant to generalized corrosion by oxygen in a neutral aqueous environment.

And what about marine environments? To resist in sea water, a stainless steel must have a PREN (Pitting Resistance Equivalent Number index used to evaluate the corrosion resistance of stainless steels) greater than 40. Marine Grade Steel is a type of stainless steel which has the denomination, precisely, marine grade for its main characteristic, i.e. maximum resistance to any type of atmospheric agent and in particular to the corrosive force of the sea. It is classified as 316 or AISI 316 steel.

👉 The resistance of each Inoxstyle product is guaranteed for ten years, thanks to the very high quality of AISI 316L stainless steel and the craftsmanship that we dedicate to each shower.

To prevent corrosion from being triggered on stainless steel, in addition to choosing the type of material appropriately according to the service for which it is intended, it is also advisable to follow some precautions during processing and installation.

In the meantime, it is necessary to avoid contamination with less noble materials (such as common steel) both during the storage of the products, during the transformation during the manufacturing process and during installation.

It is also imperative to be careful when cleaning stainless steel. Sometimes, a basic treatment with water and soap or water and soda is sufficient to effectively clean stainless steel surfaces. In cases where the dirt is much more resistant or where it is necessary to proceed with pickling and decontamination, it is possible to use special paste products to be used locally on the area to be treated.

In the wide range of its services, Inoxstyle offers the most suitable treatments to avoid corrosive phenomena, entrusting operations such as polishing and pickling to professionals, i.e. an intensive cleaning action that eliminates unwanted surface layers from metals.