GB/T 19292.1-2018Corrosion of metals and alloys -- Corrosivity of atmospheres -- Part 1: Classification, determination and estimation (English PDF)

4.1 symbol

The following symbols apply to this document.

Rcorr. Corrosion rate in the first year of atmospheric exposure.

T. air temperature.

Pd. Sulfur dioxide deposition rate.

Pc. sulfur dioxide concentration.

Sd. chloride ion deposition rate.

tau. wet time.

4.2 Abbreviations

The following abbreviations apply to this document.

C. Atmospheric corrosion grade.

RH. Relative humidity.

1.3 \u003crcorr<=25

0.7 \u003crcorr<=5

0.1 \u003crcorr<=0.7

0.9 \u003crcorr<=5

0.1 \u003crcorr<=0.6

Rcorr<=0.6

Table 2 (continued)

Corrosive

grade

Metal corrosion rate rcorr

Unit carbon steel zinc, copper and aluminum

C3

g/(m2.a)

Mm/a

0.7 \u003crcorr<=2.1

0.6 \u003crcorr<=1.3

0.6 \u003crcorr<=2

C4

g/(m2.a)

Mm/a

2.1 \u003crcorr<=4.2

1.3 \u003crcorr<=2.8

4.2 \u003crcorr<=8.4

2.8 \u003crcorr<=5.6

8.4 \u003crcorr<=25

5.6 \u003crcorr<=10

Rcorr >10

NOTE 1 The classification criteria are based on the determination of the corrosion rate of standard specimens for corrosive evaluation (see ISO 9226).

Note 2. The corrosion rate expressed in grams per square meter is converted to micrometers per year and rounded off.

Note 3. Standard metal material characterization can be found in ISO 9226.

Note 4. Aluminum is subject to uneven corrosion and localized corrosion. The corrosion rates listed in the table are calculated as uniform corrosion. Maximum pitting depth and pitting pit

Quantity is the best indicator of potential disruption, depending on the final application. Inhomogeneous corrosion due to passivation and progressively lower corrosion rates

And localized corrosion cannot be used for evaluation after the first year of exposure.

Note 5. The corrosion rate exceeds the upper limit of the C5 level is an extreme case. Corrosion grade CX refers to specific marine and marine industrial environments (see Appendix C).

8.1 General requirements for corrosion assessment

If the corrosion level cannot be determined according to the standard sample exposure, the resulting corrosion loss can be calculated according to environmental data or according to the environment.

Corrosion assessment of conditions and exposure conditions.

8.2 Normative Corrosion Assessment Based on Calculated Corrosion Loss in the First Year

The dose-response functions of the following four standard metals describe the corrosion damage associated with dry deposition of sulfur dioxide, chloride after the first year of outdoor exposure

Changes in dry deposition, temperature and relative humidity. These functions are based on the results of on-site exposure to corrosion worldwide and cover this section.

The climatic conditions and pollution conditions within the scope. See Appendix A for some limitations and uncertainties.

Dose-response function for calculating the first year corrosion loss of structural metals.

Carbon steel selection formula (1).

Rcorr=1.77.P0.52d .exp(0.020.RH fSt) 0.102.S0.62d .exp(0.033.RH 0.040.T)

(1)

among them.

Rcorr---the first year corrosion rate of metal, in micron per year (µm/a);

T --- annual average temperature in degrees Celsius (°C);

RH---annual average relative humidity, %;

Pd --- annual average SO2 deposition rate in milligrams per square centimeter [mg/(cm2.d)];

Sd --- annual average Cl-deposition rate in milligrams per square centimeter of day [mg/(cm 2 . d)];

fSt---carbon steel correlation coefficient.

fSt=0.150.(T-10) when T<=10°C; otherwise, -0.054.(T-10)

N=128, R2=0.85

Zinc selection formula (2).

Rcorr=0.0129.P0.44d .exp(0.046.RH fZn) 0.0175.S0.57d .exp(0.008.RH 0.085.T)

(2)

among them.

Rcorr---the first year corrosion rate of metal, in micron per year (µm/a);

T --- annual average temperature in degrees Celsius (°C);

RH---annual average relative humidity, %;

Pd --- annual average SO2 deposition rate in milligrams per square centimeter [mg/(cm2.d)];

Sd --- annual average Cl-deposition rate in milligrams per square centimeter of day [mg/(cm 2 . d)];

fZn---Zinc correlation coefficient.

fZn=0.038.(T-10) when T<=10°C; otherwise, -0.071.(T-10)

N=114, R2=0.78

Copper selection (3).

Rcorr=0.0053.P0.26d .exp(0.059.RH fCu) 0.01025.S0.27d .exp(0.036.RH 0.049.T)

(3)

among them.

Rcorr---the first year corrosion rate of metal, in micron per year (µm/a);

T --- annual average temperature in degrees Celsius (°C);

RH---annual average relative humidity, %;

Pd --- annual average SO2 deposition rate in milligrams per square centimeter [mg/(cm2.d)];

Sd --- annual average Cl-deposition rate in milligrams per square centimeter of day [mg/(cm 2 . d)];

fCu---copper correlation coefficient.

fCu=0.126.(T-10) when T<=10°C; otherwise, -0.080.(T-10)

N=121, R2=0.88

Aluminum selection (4).

Rcorr=0.0042.P0.73d .exp(0.025.RH fAl) 0.0018.S0.60d .exp(0.020.RH 0.094.T)

(4)

among them.

Rcorr---the first year corrosion rate of metal, in micron per year (µm/a);

T --- annual average temperature in degrees Celsius (°C);

RH---annual average relative humidity, %;

Pd --- annual average SO2 deposition rate in milligrams per square centimeter [mg/(cm2.d)];

Sd --- annual average Cl-deposition rate in milligrams per square centimeter of day [mg/(cm 2 . d)];

fAl--- aluminum correlation coefficient.

fAl=0.009.(T-10) when T<=10°C; otherwise, -0.043.(T-10)

N=113, R2=0.65

The detailed information of the environmental parameters is shown in Table 3. Table 3 also shows the measurement interval of the parameters. If 0.8Pc is used instead of dose-response function

Pd, then as explained in the note to Table 3, Pc should be the annual average.

Table 3 Parameters used to derive the dose-response function, including symbols, descriptions, intervals, and units

Symbol description interval unit

T temperature -17.1~28.7 °C

RH relative humidity 34~93 %

Pd SO2 deposition rate 0.7~150.4 mg/(cm2.d)

Sd Cl-deposition rate 0.4~760.5 mg/(cm2.d)

The sulfur dioxide (SO2) value determined according to the precipitation method (Pd) and the volumetric method (Pc) is equivalent for this part. The relationship between the two measurement methods is close

It is expressed as Pd=0.8Pc [Pd is expressed in mg/(cm2.d), and Pc is used in µg/cm3].

Note. All parameters are expressed as an annual average.

Care should be taken when the extrapolation equation is outside the range of environmental parameters (such as the coastal environment).

8.3 Informational Corrosion Assessment Based on Exposure Conditions

Atmospheric environmental corrosivity increases under the influence of temperature-humidity combined with wet weather and other corrosive substances.

Appendix B gives the typical atmospheric pollution levels.

Exposure conditions (location grade) of materials, parts or structural parts affect the environmental effects.

See Appendix C for a typical environmental qualitative description of atmospheric corrosivity ratings for informative corrosivity assessments.

Appendix A

(informative appendix)

Source of uncertainty regarding atmospheric corrosivity determination and assessment

A.1 General requirements

The corrosiveness of the atmospheric environment should be based on the corrosion grade determined by the exposure of the sample or the rot determined according to the environmental parameters and the dose-response equation.

Corrosion grades are classified. The use of these two different levels of corrosivity assessment means that assays (low uncertainty) and assessments occur

Method (high uncertainty) Two different levels of uncertainty. This appendix is used to determine the uncertainty of these two levels.

The detailed information listed in this appendix is based on an independent statistical analysis related to the evaluation of the dose-response function derivation.

A.2 Error distribution

The corrosion rate appears as a lognormal distribution, such as a lognormal distribution. If the uncertainty is in the standard deviation of the logarithm S table

Show, then

deltaln(rcorr)=+/-s (A.1)

among them.

Rcorr---the first year corrosion rate of metal, in micron per year (µm/a);

s --- standard deviation.

This indicates that the uncertainty interval is usually asymmetrical and can be expressed as rcorr.e+/-s. When s is small, the interval is roughly symmetrical.

The following examples can be used. When s = 0.7, then es = 2, es = 1/2, which corresponds to an interval from -50% to 100%. phase

Conversely, when s = 0.01, then es = 1.01, es = 0.99, which corresponds to an interval from -1% to 1%.

A.3 Uncertainty level

Table A.1 gives the evaluation level of uncertainty. From the table, there is a huge difference between the two methods, which drives two different parties.

The development of law. A.4 gives the possible sources of error and explains the error given in Table A.1.

Table A.1 Uncertainty in assessment of corrosion grade based on assay (sample exposure) and evaluation method (dose-response function)

metal

uncertainty

Assay method

Carbon steel +/-2% -33%~ 50%

Zinc +/-5% -33%~ 50%

Copper +/- 2% -33% ~ 50%

Aluminum +/-5% -50%~ 100%

A.4 Source of uncertainty

For corrosive grades determined from exposure to the specimen, the first thing to clarify is that the values given in Table A.1 represent three independent values.

Calculate the average value instead of a single corrosion value.

The level of uncertainty given in Table A.1, including the method of determination and evaluation, is based on the material at different test sites and the same exposure cycle.

Exposure results. Therefore, these values are universal, but the corrosion damage changes with the natural environment and climate change each year. These changes are not

It is included in the values given in Table A.1.

For the level of corrosivity evaluated according to the dose-response function, the total uncertainty consists of two parts, the uncertainty of the dose-response function.

Uncertainty in the measurement of degrees and environmental parameters. Among them, the uncertainty of the dose-response function dominates. At the same time, the values given in Table A.1

It is based on the average uncertainty of the range of parameters covered in the function. For all regression functions, the uncertainty is lowest in the middle range, right

It should be at the corrosive grade C3; it is higher in the upper and lower limits, corresponding to the corrosive grades C1 and C5. Corrosion grade CX uncertainty

The highest degree and cannot be calculated in this way.

Appendix B

(informative appendix)

Atmospheric characteristics related to atmospheric corrosivity

For the data corrosivity assessment method, it is necessary to make the parameter selection simple and easy for the user to master. In this section, metal and

The key factors for atmospheric corrosion of alloys are the combined effects of temperature and humidity, as well as the levels of sulfur dioxide and chloride contamination.

For unshielded locations, the effects of corrosion are in terms of dry settling and wet settling. Wet settling includes the transfer of rainwater, while dry settling refers to

Transmission of other processes.

For a sheltered location, only dry settling occurs. The cumulative effect of contaminants (including particulate matter) should be considered. ISO 11844-1,

Specific problems of atmospheric corrosivity in low-erosion indoor environments are described in ISO 11844-2 and ISO 11844-3.

Surface moisture is caused by many factors such as dew, rain, snowmelt and high humidity. Use a temperature greater than 0 ° C and a relative humidity greater than 80%

Time to estimate the wet time tau about the surface. In extremely cold regions, humidity times above 0 ° C and relative humidity above 80% are low

Estimated (lower freezing point).

Information on the calculation of wet time contributes to the assessment of data atmospheric corrosivity.

The wet time under different exposure conditions is shown in Table B.1.

Under the combined effect of specific temperature and humidity, the most important factor affecting atmospheric corrosion is the pollution caused by sulfur dioxide or salt in the air.

dye. The level of contamination should be measured in accordance with ISO 9225.

Other types of contaminants (oxygen nitride NOx, HNO3 and industrial dust in densely populated industrial areas) or in microenvironment

Bodywork and technical contaminants (Cl2, H2S, organic acids and ice melting salts) may also play a role. These types of contaminants are not used

Classification criteria.

According to this section, other types of pollutants should be used as associated pollutants (such as nitrogen NOx in urban atmosphere) or in specific operations.

Contaminants (such as acid mist in the microenvironment). The concentrations of the most important pollutants in different atmospheric environments are shown in Table B.2.

In many parts of the world, the concentration of sulfur dioxide is gradually decreasing, and the increase in traffic volume leads to a gradual increase in the concentration of nitrogen oxides.

Oxygen and particulate matter together create a new, polluted environment. In other parts of the world, due to rapid industrial development, pollutants of sulfur dioxide

Corrosion is exacerbated and still dominates.

The atmospheric pollutants considered in this section from the perspective of corrosive classification are divided into two categories. pollution caused by sulfur dioxide and salt in the air.

Both types of pollutants are representative in rural, urban, industrial, and marine atmospheres. For standard outdoor atmospheres, sulfur dioxide is caused

The pollution classification is shown in Table B.3.

The salt characteristics of each type of atmosphere are classified in Table B.4. It is important to consider the importance of chloride accumulation on the surface that has not been washed away by rain.

Sex, especially in wet locations.

Table B.1 Wet time under different exposure conditions

Wet time/(h/a) level example

Tau<=10 tau1 air-conditioned internal microclimate

10< tau<=250 tau2 Air-conditioned internal microclimate, except for air-conditioned interi...

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