Corrosion Resistance Classes

Guide of stainless grade selection as per EN 1993-1-4 intent and industry practice, showing Corrosion Resistance Classes (CRC I–V).

CRC Class	Typical Environment / Exposure Level	Description of Conditions	Typical Stainless Grades	Examples / Notes
CRC I	Low corrosivity (dry interior, C1–C2 ISO 9223)	Heated indoor rooms, dry offices, low humidity, no condensation	304 410	Low cost, general purpose — use indoors only
CRC II	Moderate (urban interior/exterior, low chloride)	Occasional condensation, no salt exposure, urban atmospheres	2202 Hardtec 304 316	Protected façades, dry warehouses
CRC III	Medium-high (urban/coastal atmosphere, occasional cleaning)	Moderate chlorides, industrial or coastal exposure, low wash-off	316	Exterior façades near coast, bridges inland from sea
CRC IV	High corrosivity (marine/coastal, splash or tunnel air)	Salt spray, de-icing salts, condensation, polluted tunnels	Bumax DX129 2205 Bumax SDX129	Tunnels, bridges, façades in spray zones
CRC V	Very high or extreme (chloride-rich, aggressive chemical or indoor pool environments)	Persistent condensation, chlorinated vapour, limited rain wash, high chlorides	Bumax SDX12 2507	Indoor swimming pools, wastewater plants, tunnels near sea, offshore decks
(unofficial “CRCV”)	Used informally in some German and Nordic guidance for “very severe” pool or tunnel environments	Essentially an extension of CRC V; select super austenitic or super duplex grades only	1.4529	Above swimming pools, inside road tunnels with de-icing salts

Key References

EN 1993-1-4:2015-10, Annex A – introduces CRC I–V classification for stainless structural design.
EN 10088-1/2/4/5 – defines the chemical and mechanical properties of the grades listed.
ISO 9223:2021 – defines atmospheric corrosivity (C1–C5/CX) that underpins CRC assessment.
IMOA & Euro Inox Guides – provide cross-reference of grades vs. environments.
DIN EN 1993-1-4 National Annex (Germany) – gives example mapping between CRC and environments such as “over indoor swimming pools” (CRC V) and “road tunnels” (CRC IV–V).

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