This standard specifies the corrosion types of ordinary carbon steel in different atmospheric environments and their corresponding relationship with relative humidity and the content of corrosive substances in the air. This standard is applicable to ordinary carbon steel (based on A3 steel) steel structures exposed in the open air in four atmospheric environments: rural atmosphere, urban atmosphere, industrial atmosphere (including chemical atmosphere) and marine atmosphere. GB/T 15957-1995 Atmospheric environment corrosivity classification GB/T15957-1995 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Corrosivity classification of atmospheric environment
1 Subject content and scope of application
GB/T 15957—1995
This standard specifies the corrosion types of ordinary carbon steel in different atmospheric environments and their corresponding relationship with relative humidity and the content of corrosive substances in the air.
This standard is applicable to ordinary carbon steel (based on A3 steel) steel structures exposed in the open air in four atmospheric environments: rural atmosphere, urban atmosphere, industrial atmosphere (including chemical atmosphere) and marine atmosphere. This standard is the standard for the classification of corrosion levels of exposed carbon steel in different atmospheric environments, and is also an important basis for the selection of protective coatings and similar protective materials.
2 Definitions
This standard adopts the following definitions:
2.1 Atmospheric corrosivity
The ability of the atmospheric environment (including local environment and microenvironment) to cause corrosion of a given substrate (carbon steel component). 2.2 Corrosion load
The sum of atmospheric environmental factors that promote corrosion of substrates. 2.3 Corrosion system
The system consisting of a given substrate and the total environment that affects corrosion (i.e., corrosion load). 2.4 Atmosphere
A mixture of gases (air) surrounding a given substrate, usually also including aerosols and suspended solid particles. 2.5 Atmosphere type
The characterization of various atmospheres using appropriate atmospheric classification standards. 2.5.1 Rural atmosphere
Refers to the ambient atmosphere of inland rural areas and small towns without significant corrosive pollution. 2.5.2 Urban atmosphere
Refers to the ambient atmosphere of densely populated areas without concentrated industries and with little pollution. 2.5.3 Industrial atmosphere
Refers to the ambient atmosphere polluted by local or regional industrial pollutants, i.e., the ambient atmosphere of industrial agglomeration areas. 2.5.4 Marine atmosphere
Refers to the atmosphere in offshore and coastal areas and on the sea surface (excluding splash zones). That is, it depends on the topography and the main airflow direction, and is polluted by sea salt aerosol (mainly chloride). 2.6 Local environment refers to the main environment surrounding the steel structure. This type of environment includes special meteorological and pollution parameters in the local area, which determines the corrosion rate and corrosion type of the steel structure in the local area.
2.7 Microenvironment
GB/T 15957—1995
refers to the micro-environment observable at the junction between the steel structure and the environment. The concept of micro-environment is established to assess the corrosion load of special environments.
2.8 Atmospheric environment classified by humidity
2.8.1 Humid environment
refers to the atmospheric environment with an annual average relative humidity RH>75% (including local environment and microenvironment). 2.8.2 Ordinary environment
refers to an atmospheric environment with an annual average relative humidity of RH60% to 75%. 2.8.3 Dry environment
refers to an atmospheric environment with an annual average relative humidity of RH<60%. 3 Description of atmospheric corrosion
3.1 The key factors affecting atmospheric corrosion of steel structures are the time for the moisture film to form on the surface of the steel structure and the content of corrosive substances in the atmosphere.
3.2 The formation of moisture film on the surface of steel structures (the moisture film can be so thin that it is invisible to the naked eye) is caused by the following factors. 3.2.1 Increase in relative humidity of the atmosphere.
3.2.2 Condensation occurs when the surface temperature of the steel structure reaches the dew point or below the dew point. 3.2.3 Pollution of the atmosphere, deposition of hygroscopic pollutants on the surface of the steel structure, such as sulfur dioxide, chlorides, and electrolytes brought by industrial operations.
3.2.4 Condensation, rainfall, snowmelt, etc. directly wet the surface of the structure. 3.3 The presence of corrosive substances in the atmosphere accelerates the corrosion rate of steel structures. Under the same humidity conditions, the higher the content of corrosive substances, the greater the corrosion rate. The corrosiveness of corrosive substances is related to the humidity of the atmosphere. In a high humidity (humid type) environment, the corrosiveness is large, and in a low humidity (dry type) environment, the corrosiveness is greatly reduced. If there are hygroscopic deposits (such as chlorides, etc.), corrosion will occur even if the humidity of the ambient atmosphere is very low (RH<60%).
4 Classification of atmospheric environment corrosion
4.1 Atmospheric relative humidity (RH) type
This standard divides the relative humidity of the atmosphere (including local environment and microenvironment) into the following three categories: 4.1.1 Dry type: RH<60%
4.1.2 Ordinary type: RH60%~75%
4.1.3 Wet type: RH>75%bZxz.net
4.2 Classification of corrosive substances in the atmosphere 1. Environmental gas type This standard divides the environmental gas into four types: A, B, C, and D according to the main gas components and their contents that affect the corrosion of steel structures (see Appendix A).
4.3 Corrosive environment type
This standard mainly divides the corrosion environment type into six categories based on the corrosion rate (mm/a) of carbon steel in the first year of exposure to different atmospheric environments.
The technical indicators of the corrosion environment type shall meet the requirements of Table 1. 837
Corrosion type
No corrosion
Weak corrosion
Light corrosion
Medium corrosion
Strong corrosion
Strong corrosion
Corrosion rate
0.0010.025
0. 025~0. 050
0.05~0.20
0.20~1.00
1~～5
GB/T15957—1995
Ambient gas
Type
Corrosive environment
Relative humidity
(annual average),%
60~~75
Note: In special occasions and under the action of additional corrosion load, the corrosion type should be upgraded, such as: a) Mechanical load:
1) In areas with heavy wind and sand, the steel structure is corroded due to the particles (sand, etc.) carried by the wind. 2) The surface of the steel structure is used for (people or vehicles) to pass or has heavy mechanical loads and moves regularly. b) There are often hygroscopic substances deposited on the surface of the steel structure. 838
Atmospheric environment
Rural atmosphere
Rural atmosphere,
Urban atmosphere
Rural atmosphere,
Urban atmosphere and
Industrial atmosphere
Urban atmosphere,
Industrial atmosphere and
Marine atmosphere
Industrial atmosphere
Industrial atmosphere
Gas categories
GB/T15957—1995
Appendix A
Classification of environmental gases
(Supplement)
Name of corrosive substances
Carbon dioxide
Dioxygen Sulfur dioxide
Hydrogen fluoride
Hydrogen sulfide
Nitrogen oxides
Hydrogen chloride
Carbon dioxide
Sulfur dioxide
Hydrogen fluoride
Hydrogen sulfide
Nitrogen oxides
Hydrogen chloride
Sulfur dioxide
Hydrogen fluoride
Oxygen sulfide
Nitrogen oxides
Hydrogen chloride
Sulfur dioxide
Hydrogen fluoride
Hydrogen sulfide
Nitrogen oxides
Hydrogen chloride
Corrosive substance content, mg/m2
0. 1~～~5
10~200
5～25
5～10
200～1000
10～100
25~100
10~100
Note: When the atmosphere contains multiple corrosive gases at the same time, the corrosion level should be based on the highest one or several. 839
Additional instructions:
GB/T15957—1995
This standard is proposed by the Ministry of Chemical Industry of the People's Republic of China. This standard is issued by the National Technical Committee for Standardization of Coatings and Materials. This standard is drafted by the Marine Coatings Research Institute of the Ministry of Chemical Industry and Beijing University of Science and Technology. Participating drafting units of this standard: Changzhou Coatings Chemical Research Institute of the Ministry of Chemical Industry, Shanghai Baosteel No. 20 Metallurgical Enterprise Development Corporation, Wujin Kaixing Coating Factory, Yangzi Petrochemical Company, Tianjin Seawater Desalination Research Institute. The main drafters of this standard are Liu Peimin, Liang Huamin, Xiao Heng and Su Mei.
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