Materials, corrosion and risk

Atmospheric Corrosivity

大气腐蚀性

Atmospheric corrosivity is the capacity of a local atmospheric environment to cause corrosion of metals, classified or estimated using a defined method and material basis.

Aliases: corrosion risk, corrosivity of atmosphere

QUANTITY, SYMBOL AND UNIT

Quantity / objectAtmospheric corrosivity

UnitNot applicable

Definition

Atmospheric corrosivity is the capacity of a local atmospheric environment to cause corrosion of metals, classified or estimated using a defined method and material basis.

ISO 9223 identifies the temperature-humidity complex, sulfur dioxide pollution and airborne salinity as key atmospheric factors. Humidity matters through surface wetness and exposure, but it is only one part of the corrosive environment.

Relations and distinctions

Corrosivity and relative humidity

RH is an air-state ratio; atmospheric corrosivity describes the combined corrosion severity for stated materials and exposure conditions.

Corrosivity and corrosion damage

Corrosivity describes an environment or category. Actual component damage also depends on material, coating, geometry, contaminants, duration and maintenance.

Engineering meaning

Assess humidity together with pollutants, salinity, surface temperature, wetness duration and the selected material system.
Use material, coating and enclosure decisions that match the verified service atmosphere rather than an RH value alone.

Common misconceptions

MisconceptionKeeping RH below one universal value eliminates corrosion risk in every industrial enclosure.

Accurate explanationCorrosion also depends on pollutants, salts, surface conditions, materials and exposure time; no single RH threshold covers every atmosphere.

Application boundaries

ISO 9223's public scope does not characterize specific chemical or metallurgical service atmospheres.
A glossary entry cannot assign a corrosivity category without the required site data, specimen results or standard method.

Supporting sources

International Organization for Standardization / SRC-ISO-9223-2012

ISO 9223:2012 - Corrosion of Metals and Alloys - Corrosivity of Atmospheres - Classification, Determination and Estimation ↗

Second edition, confirmed 2022 / ISO public abstract and scope for classification, determination and estimation of atmospheric corrosivity
Supports: Atmospheric corrosivity is classified by first-year corrosion rates of standard specimens; Temperature-humidity complex, sulfur dioxide pollution and airborne salinity are key factors; The standard does not characterize specific chemical or metallurgical service atmospheres

Maintenance record