Selection of envelope structures for construction in aggressive environments

 

The DSTU ISO 12944-2 standard describes six categories of corrosion activity, which are determined by the conditions of the external or internal environment. For the medium, high and extreme categories, it is recommended that materials and coatings for envelope structures be selected individually, considering all factors of influence and operating conditions, as this ultimately determines their durability.

 

Atmospheric corrosivity categories and examples of typical environments according to DSTU ISO 12944-2

Corrosion aggressivity category	The attachments of typical environments
	Outside the premises	Inside the premises
C1 very low	–	Heated buildings with clean air, e.g. offices, shops, schools, hotels
C2 low	Low-pollution environment: primarily rural areas	Unheated buildings where condensation can occur, e.g. warehouses, sports halls
C3 medium	Urban and industrial environment, moderate sulphur dioxide pollution; coastal areas with low salinity	Industrial premises with high humidity and certain air pollution, such as food processing plants, laundries, breweries, dairies
C4 high	Industrial areas and coastal areas with moderate salinity	Chemical plants, swimming pools, coastal vessels and shipyards
C5 very high	Industrial areas with high humidity and aggressive environment, as well as coastal areas with high salinity	Buildings or areas with almost constant condensation and high air pollution
CX extreme	Offshore areas with high salinity; industrial areas with extremely high humidity and corrosive environments, as well as subtropical and tropical environments	Industrial areas with extremely high humidity and aggressive atmospheres

 

 

For example, in very aggressive environments, the incorrect choice of the type and thickness of the polymer coating of the sandwich panel cladding can lead to through corrosion and their destruction after several years of operation.

 

 

To select durable materials from light gauge steel, it is necessary to contact a qualified supplier at the design stage of the enclosure. The selection of envelope structures for use in aggressive environments is carried out individually and usually involves determining the characteristics of the environment, the optimal choice of materials and fasteners, and the development of structural joints.

 

Determining the operating conditions of structures

 

At the beginning of the project, a questionnaire is filled out indicating the general characteristics of the building, technology features and known parameters of the external and internal environments, as well as the intended technological procedures.

 

If required, Rauta provides on-site surveys using modern measurement methods to determine the following parameters:

 

• Air temperature and humidity, duration and cyclicality of their effect
• Environmental pollution, including the presence and concentration of acids, alkalis or other aggressive elements
• Availability and frequency of additional treatment of structures with detergents or disinfectants

 

 

As a result, the client receives a report with detailed results of the environmental characteristics research.

 

Selection of wall and roof structures

 

After analyzing the results of the study, Rauta provides recommendations for the best protection of steel facades and roofs, indicating the following parameters:

 

• Steel grade and thickness. It is recommended to use structural steel grades with guaranteed yield strength (S280-S350, AISI 304, AISI 316, etc.) for load-bearing and enclosing structures and avoid using DX steel. The thickness of coated steel used in medium and high aggressiveness environments should be at least 0.5 mm. Coated steel, stainless steel, or Cor-ten steel can be used in such environments.
• Degree of galvanization. The corrosion resistance provided by a zinc coating is directly proportional to its thickness. For aggressive environments, it is recommended to use steel with a zinc coating from Zn275 (mass fraction of zinc 275 g/m², coating thickness 20 microns on each side) to Zn600 (42 microns). At the maximum degree of Zn600 galvanization, the service life of galvanized steel without a polymer coating can reach 80 years. When using products made of galvanized steel without a polymer coating, it is necessary to take into account the loss of zinc from the surface. For example, in a C4 environment for 275 g/m²-galvanized steel without a polymer coating, the complete loss of zinc occurs in 25 years.
• Polymer/laminate coating. For highly aggressive environments, it is not recommended to use the most common coating Polyester. It is necessary to use a coating whose thickness varies from 27 microns for Hiarc to 120 microns for FoodSafe laminate. The most resistant to corrosion are Pural, Hiarc and FoodSafe coatings. More information about the features of polymer coating selection can be found in the article. For more than 40 years, Ruukki-SSAB has been testing samples for UV and corrosion resistance in natural conditions at its own test sites around the world. The test methodology complies with the European standard EN 10169+A1, which allows for in-depth research into the effects of various environments on coatings and their improvement.
  

  Ruukki-SSAB test site for testing coated steel samples

• If sandwich panels are used as envelope structures, you should also pay attention to the type of filler. For damp rooms, the best filler is non-hygroscopic PIR, and for buildings with a high fire hazard, mineral wool. The durability of mineral wool panels is significantly affected by the quality of the adhesive used between the cladding and the filler, as well as the technology of its application.
• Additional surface protection. If the environment is highly aggressive, the surface of the envelope structures can be additionally protected in the form of paint, resin or a structural barrier made of other materials at the points of highest concentration.
• For load-bearing and self-supporting elements, such as corrugated board or sandwich panels, it is mandatory to calculate the load-bearing capacity to withstand loads over time. For this purpose, special programmes such as Traypan and Poimu are used.

 

Selection of fasteners

 

To ensure the durability of a building, it is necessary to pay attention not only to the materials of the envelope structure, but also to the fasteners. The level of resistance of fasteners in aggressive environments should be no less than that of the structure coating.

 

Corrosion aggressiveness category	Recommended fastener material
C1	Zinc-coated steel with a thickness of 8-12 µm
C2	Zinc-coated steel with a thickness of 8-12 µm
C3	Zinc-coated steel with a thickness of more than 45 microns, or ceramic-organic coating, or stainless steel A2 grade
C4	Stainless steel A2 grade
C5	Stainless steel A4 grade
CX	Stainless steel A4 grade

 

The type of fastener is selected depending on the design features of the element connection.

 

 

Development of design solutions

 

The operation of steel facades and roofs in environments with increased aggressiveness imposes a number of requirements on structural joints, joint tightness, drainage, etc. Rauta specialists develop a detailed design of the necessary structural solutions, considering the technological features of the building (vibrations, electromagnetic loads, etc.) in such a way as to ensure the long-term operation of the facility, as well as high aesthetic and thermal properties of the envelope structures.

 

 

When Ruukki materials are supplied, the client is provided with a project warranty for the products under certain conditions of use. At the same time, the effective service life of the products is usually much longer than indicated in the warranty letter.

 

Rauta has extensive experience in supplying sandwich panels and ventilated facade cladding to facilities with increased environmental aggressiveness. Therefore, it can guarantee that the client will receive products that will meet the operating conditions in the best possible way. Upon delivery, Rauta additionally provides a full package of accompanying documents, including: recommendations for handling and operation, installation instructions, design solutions, load-bearing capacity calculations, etc.