Selecting the appropriate steel for use in a corrosive environment classified as C4 (according to ISO 9223) is crucial. Will stainless steel be sufficient, or is a special protective coating necessary? The classification of atmospheric corrosive environments is carried out according to the standards PN-EN ISO 12944-2 and PN-EN ISO 12500. Additionally, the assessment of atmospheric corrosivity is based on the level of deposition of pollutants such as SO2 and Cl-, and the measurement of industrial dust precipitation, according to PN-ISO 9225, PN-ISO 9223, and PN-67/Z-04010 standards. The C4 corrosive environment is characterized by high corrosivity. Examples of such areas include industrial and coastal regions with medium salinity, as well as chemical plants, swimming pools, and ship and boat repair yards.
Stainless steel fasteners are classified according to the PN-EN ISO 3506 standards, while corrosion-resistant stainless steel grades are covered by the PN-EN 10088-1-5 standards. Based on these standards, Table 1 has been developed, presenting recommended stainless steel grades depending on the atmospheric conditions.
The decision to use stainless steel in a specific environment depends on the location of the elements—whether they are inside or outside the structure. Regular surface maintenance, through periodic cleaning, enhances the durability and reliability of stainless steel components.
Stainless steels used in the discussed corrosive environment do not require additional protective coatings. Selecting the appropriate material based on corrosion resistance—particularly pitting and crevice corrosion associated with molybdenum and chromium content—is essential.
| Environmental category according to PN-EN ISO 12500 | Stainless steel grades according to PN-EN 10088 and PN-EN ISO 3506 | Recommendations |
|---|---|---|
|
C1 – very small C2 – small |
1.4301, 1.4307, 1.4541 (Cr-Ni steels) (steels A1, A2, A3 according to ISO 3506) |
Provided that proper surface maintenance is ensured, stainless steels without added molybdenum can be used. |
|
C3 – medium |
1.4301, 1.4307, 1.4541 (Cr-Ni steels) (steels A1, A2, A3 according to ISO 3506) 1.4404, 1.4571, 1.4362 (Cr-Ni-Mo steels) (steels A4, A5 according to ISO 3506) |
For environments with higher humidity, stainless steels containing molybdenum should be used. |
|
C4 – high |
1.4404, 1.4571, 1.4362 (Cr-Ni-Mo steels) (steels A4, A5 according to ISO 3506) |
Only grades containing added molybdenum should be used. |
|
C5 – very high |
1.4404, 1.4571, 1.4362 (Cr-Ni-Mo steels) (steels A4, A5 according to ISO 3506) 1.4439, 1.4539, 1.4547, 1.4462 (high-alloy Cr-Ni-Mo steels) |
Only high-alloy grades containing added molybdenum should be used. |
Selecting the right stainless steel grade for a C4 corrosive environment is crucial. The choice depends on the location of the elements and regular surface maintenance. For environments of category C4, it is recommended to use grades containing molybdenum to ensure appropriate corrosion resistance.
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