Let’s find out why Forme d’Acqua uses AISI 316 and 316L stainless steel in its fountains
In constructing a fountain or a water feature, the choice of using AISI 304, 316 or 316L steel is crucial to ensure its durability and beauty in the long term. The use of one type of stainless steel instead of another can compromise the result of the project and lead to the appearance of unsightly brown spots caused by oxidation.
AISI 304 and AISI 316 are two types of stainless steel commonly used in the production of industrial products, such as pipes, valves, and equipment in general. Although they are both excellent quality materials, they have important differences that it is important to know, because they determine the choice of one type of steel instead of another within the projects of fountains or water features.
First of all, however, terms such as stainless steel, stainless steel, AISI must be clarified, which are in common use, but we do not always have a clear understanding of their meaning and therefore their correct application.
Stainless means that the material is resistant to oxidative and corrosive processes, i.e. that it does not structurally alter due to the action of humidity and oxygen in the air.
Inox is just the abbreviation of the French term inoxydable and is an acronym used mainly for commercial purposes.
AISI is the nomenclature deriving from the acronym of American Iron and Steel Institute, the US unification institute for iron and steel.
Stainless steel is the term used to identify the families of steels (austenitic, ferritic, martensitic) with a minimum chromium content of at least 11%, an element that offers to the material greater resistance to oxidation and corrosion than ordinary non-metallic steel (also called carbon steel). It is made up of various elements, such as:
- iron, the main alloying element, present for over 50%;
- chromium, which increases the hardness and the limit of elasticity;
- nickel, which gives toughness, also favoring self-passivation;
- molybdenum, mainly used to increase resistance to corrosion.
Stainless steels are resistant to corrosion thanks to passivation: a phenomenon which consists in the formation of a thin protective film, which occurs whenever a clean surface is exposed to an aggressive environment (air or water) which can supply enough oxygen to form a surface layer of chromium oxide.
AISI 304 is the most common type of stainless steel, composed of approximately 18% chromium and 8% nickel. It is generally used for the construction of industrial products, but it is NOT suitable for use in highly corrosive or chlorinated environments, such as swimming pools or water treatment plants, as it will cause brownish stains and lower durability of the material.
In contrast, AISI 316 steel is composed of approximately 16% chromium, 10% nickel and 2% molybdenum. Even if present only in a small percentage, molybdenum makes AISI 316 steel more resistant to corrosion – so much so that it is also called “marine steel” –, therefore suitable for use in highly corrosive environments (where there is salt water or water with high levels of chlorine) and for the production of parts for fountains or in water treatment plants. Furthermore, in terms of mechanical strength, AISI 316 has a lower tolerance to deformation than AISI 304.
AISI 316 stainless steel is a steel destined to last dozens and dozens of years, the important thing is to carry out minimal and little laborious maintenance, passing a coat of protective product once a year, such as vaseline oil, or a specific one to temporarily restore passivation.
Ultimately, AISI 316 steel is clearly superior to AISI 304, due to a series of factors which determine a greater duration in the long term, and this is why the cost is significantly higher, depending on the period varies 30 to 45% more.
Dealing with the differences between AISI 316 and AISI 316L steel, there is a characteristic that makes them unique from each other: compared to AISI 316, AISI 316L steel has a high chromium and molybdenum content combined with a low carbon content, which makes it even less susceptible to corrosion. In addition, AISI 316L is also softer and more malleable in machining than AISI 316, making it the ideal choice for applications that require components with precise shapes and clean, strong welds.
Both AISI 316 and AISI 316L stainless steels are excellent choices for their respective applications, mainly for the construction of fountains, water features and installations that are constantly in contact with water treated with acid and chlorine. Therefore, if you want to guarantee the highest quality to a fountain, you have to choose AISI 316 or 316L steel, instead for welded products, the best is AISI 316L steel. As previously mentioned, 304 steel is a good quality stainless steel, but to be reserved for the creation of products that are not intended for quality fountains or water features with the aim of being durable over time.
February 13th 2023