When aluminium is advantageous
The main advantage of aluminium alloys is low density. Lower self-weight can reduce support loads and simplify installation of large structures.
The natural oxide film provides good resistance in many atmospheric conditions, but compatibility with the specific product and cleaning agents must still be checked separately.
GOST 4784-2019 classifies wrought aluminium alloys by alloying system and specifies their chemical composition. This provides a basis for material identification, but a grade standard does not replace structural calculation, weldability checks or corrosion assessment in the intended environment.
For food-contact products, GOST 4784 provides an additional “Sh” marking for relevant grades and limits certain impurities. This does not make every aluminium grade automatically suitable for food use: suitability must be supported by documentation and requirements for the specific product.
When stainless steel is chosen
Stainless steels are often used where hygiene, regular washing and resistance to particular process media are especially important.
However, stainless steel is not a single material. Corrosion resistance depends on the grade, temperature and chemical composition of the medium.
GOST 5632-2014 covers corrosion-resistant, oxidation-resistant and high-temperature-strength steels and alloys and defines their grades. The word “stainless” alone is insufficient: austenitic, ferritic and other classes differ in their resistance to chloride, acidic, alkaline and high-temperature environments.
What material grade standards provide for the designer
GOST 4784-2019 and GOST 5632-2014 primarily identify materials and their chemical compositions unambiguously. This is the starting point: properties of the specific sheet, profile or tube are then confirmed by its product standard, quality certificate and design codes.
Silo material selection uses a set of criteria rather than “aluminium is lighter, stainless steel is stronger”: product, temperature, moisture, hygiene, cleaning method, external atmosphere, welds, structural weight and life-cycle cost.
| Document | What it confirms | What it does not establish on its own |
|---|---|---|
| GOST 4784-2019 | Grade and chemical composition of a wrought aluminium alloy | Strength of a particular sheet or suitability of the structure for a given medium |
| GOST 5632-2014 | Grade and class of corrosion-resistant/heat-resistant steel or alloy | Guaranteed resistance to every product and cleaning regime |
| SP 359.1325800.2017 | Steel silo design approach and product loads | Automatic applicability of the same rules to an aluminium structure |
Material comparison
| Criterion | Aluminium alloys | Stainless steel |
|---|---|---|
| Structural weight | Usually lower | Usually higher |
| Atmospheric resistance | High with appropriate design | High, depending on grade |
| Hygienic design | Possible with appropriate surface treatment | Often selected for intensive cleaning |
| Thermal conductivity | Higher | Lower |
| Grade selection | Depends on strength and environment | Critical for chemical resistance |
Sespel’s industrial experience
Sespel’s catalogue groups aluminium and stainless steel silos in a dedicated range, allowing material selection for the product and operating conditions. The aluminium design uses extruded profiles and friction stir welding, with diameters of 2.4–4 m and capacities of 30–240 m³.
Practical material selection considers several factors: chemical compatibility, sanitation requirements, external environment, structural weight and ownership cost.
How the product affects selection
Dry neutral powders emphasise weight, cost and installation conditions. Food ingredients add surface and cleaning requirements. For chemically active media, compatibility of the specific alloy becomes decisive.
Even within a single plant, different products may require different shell materials.
Cleaning and sanitation deserve particular attention: cleaning agent chemistry, concentration, temperature and contact duration may affect corrosion more critically than the stored product itself.
Why ownership cost matters
Metal price is only part of the budget. Foundations, supports, transport, installation, cleaning, inspection and repairability affect the total.
A more expensive material may be more economical over a long life cycle; in other cases, high-alloy steel offers no practical benefit.
A practical selection approach
- establish product properties and cleanliness requirements;
- describe cleaning conditions and the external environment;
- account for weight and foundation limits;
- compare installation and maintenance needs;
- confirm material compatibility before issuing detailed design documentation.
Sources and technical materials
- GOST 4784-2019 — Aluminium and wrought aluminium alloys. Grades
- GOST 5632-2014 — Alloyed stainless, corrosion-resistant, oxidation-resistant and high-temperature-strength steels and alloys. Grades
- SP 359.1325800.2017 — Vertical cylindrical steel silos for bulk products. Design rules
- EN 1999 series — Design of aluminium structures
- EN 1993 series — Design of steel structures
The applicable regulatory requirements depend on the product’s intended use, industry, jurisdiction and project specification.