The selection of stainless steels for architectural applications depends mainly on their corrosion resistance. The decisive factor is the location of the structure in a specific outdoor environment and conditions such as temperature and humidity. The service environment can be divided into rural, urban, industrial and coastal areas.
Rural areas are unpolluted areas, away from industry. Urban areas are residential, commercial or light industrial zones, with pollution coming mainly from road traffic. Industrial areas contain pollutants emitted by chemical plants. Coastal areas are characterised by the presence of seawater in the atmosphere.
It should be borne in mind that the service environment may change, which affects the level of pollution. A microclimate may also change the classification of an area. Depending on temperature and humidity, the risk of corrosion may vary.
The choice of steel grade depends on the application. Grade 1.4301 / 1.4307 is suitable for most applications, while 1.4401 / 1.4404 is recommended where corrosion requirements are higher. Additional factors such as surface finish, structural design, fabrication methods and required mechanical properties must be taken into account.
| Steel type | Rural area | Urban area | Industrial area | Coastal area | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| L | M | H | L | M | H | L | M | H | L | M | H | |
| 1.4301 (AISI 304) / 1.4307 (AISI 304L) | + | + | + | + | + | ⊖ | ⊖ | ⊖ | – | + | ⊖ | – |
| 1.4401 (AISI 316) / 1.4404 (AISI 316L) | ⊕ | ⊕ | ⊕ | ⊕ | + | + | + | + | ⊖ | + | + | ⊖ |
| High-alloy grades * | ⊕ | ⊕ | ⊕ | ⊕ | ⊕ | ⊕ | ⊕ | ⊕ | + | ⊕ | ⊕ | + |
| * – High-alloy grades in order of increasing corrosion resistance: 1.4439 (AISI 317LMN); 1.4539 (AISI 904L); 1.4547; 1.4462 (AISI 2205) | ||||||||||||
Environment characteristics:
L – Low risk of corrosion – low humidity and low temperature
M – Typical conditions for the given area
H – Severe atmospheric conditions: high humidity, high temperature or high level of pollution
Corrosion resistance rating:
+ – The best choice in terms of corrosion resistance and cost.
– – High probability of corrosion.
⊕ – Suitable for use, but the grade may be over-specified in terms of corrosion resistance and cost.
⊖ – May be used if an appropriate surface finish quality and regular cleaning are maintained.
The durability of stainless steels in exterior architectural applications is also affected by the type of surface finish. In general, the smoother the surface – i.e. the lower its roughness – the higher the corrosion resistance of the steel. Correct structural design is also important. In particular, crevices that may promote the development of corrosion should be avoided. Appropriate fabrication and joining methods must be used to avoid contamination and damage to the steel surface. The use of stainless steel fasteners is recommended. Regular cleaning of the surfaces of stainless steel components is also important, and its frequency depends on local conditions. If periodic cleaning is difficult to carry out for a given structure, it is advisable to choose a steel with higher corrosion resistance.
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