ASTM G101-04(2010)
(Guide)Standard Guide for Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels
Standard Guide for Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels
SIGNIFICANCE AND USE
In the past, ASTM specifications for low-alloy weathering steels, such as Specifications A242/A242M, A588/A588M, A606 Type 4, A709/A709M Grade 50W, HPS 70W, and 100W, A852/A852M, and A871/A871M stated that the atmospheric corrosion resistance of these steels is “approximately two times that of carbon structural steel with copper.” A footnote in the specifications stated that “two times carbon structural steel with copper is equivalent to four times carbon structural steel without copper (Cu 0.02 maximum).” Because such statements relating the corrosion resistance of weathering steels to that of other steels are imprecise and, more importantly, lack significance to the user (1 and 2) , the present guide was prepared to describe more meaningful methods of estimating the atmospheric corrosion resistance of weathering steels.
The first method of this guide is intended for use in estimating the expected long-term atmospheric corrosion losses of specific grades of low-alloy steels in various environments, utilizing existing short-term atmospheric corrosion data for these grades of steel.
The second method of this guide is intended for use in estimating the relative atmospheric corrosion resistance of a specific heat of low-alloy steel, based on its chemical composition.
It is important to recognize that the methods presented here are based on calculations made from test data for flat, boldly exposed steel specimens. Atmospheric corrosion rates can be much higher when the weathering steel remains wet for prolonged periods of time, or is heavily contaminated with salt or other corrosive chemicals. Therefore, caution must be exercised in the application of these methods for prediction of long-term performance of actual structures.
SCOPE
1.1 This guide presents two methods for estimating the atmospheric corrosion resistance of low-alloy weathering steels, such as those described in Specifications A242/A242M, A588/A588M, A606 Type 4, A709/A709M grades 50W, HPS 70W, and 100W, A852/A852M, and A871/A871M. One method gives an estimate of the long-term thickness loss of a steel at a specific site based on results of short-term tests. The other gives an estimate of relative corrosion resistance based on chemical composition.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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Standards Content (Sample)
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Designation: G101 − 04(Reapproved 2010)
Standard Guide for
Estimating the Atmospheric Corrosion Resistance of Low-
Alloy Steels
This standard is issued under the fixed designation G101; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Structural Steel Plate With Atmospheric Corrosion Resis-
tance
1.1 This guide presents two methods for estimating the
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
atmospheric corrosion resistance of low-alloy weathering
sion Test Specimens
steels, such as those described in Specifications A242/A242M,
G16 Guide for Applying Statistics to Analysis of Corrosion
A588/A588M, A606 Type 4, A709/A709M grades 50W, HPS
Data
70W, and 100W, A852/A852M, and A871/A871M. One
G50 Practice for Conducting Atmospheric Corrosion Tests
method gives an estimate of the long-term thickness loss of a
on Metals
steel at a specific site based on results of short-term tests. The
other gives an estimate of relative corrosion resistance based
3. Terminology
on chemical composition.
3.1 Definitions of Terms Specific to This Standard:
1.2 The values stated in SI units are to be regarded as
3.1.1 low-alloy steels—Iron-carbon alloys containing
standard. No other units of measurement are included in this
greater than 1.0 % but less than 5.0 %, by mass, total alloying
standard.
elements.
3.1.1.1 Discussion—Most “low-alloy weathering steels”
2. Referenced Documents
contain additions of both chromium and copper, and may also
2.1 ASTM Standards:
contain additions of silicon, nickel, phosphorus, or other
A242/A242M Specification for High-Strength Low-Alloy
alloying elements which enhance atmospheric corrosion resis-
Structural Steel
tance.
A588/A588M Specification for High-Strength Low-Alloy
Structural Steel, up to 50 ksi [345 MPa] Minimum Yield
4. Summary of Guide
Point, with Atmospheric Corrosion Resistance
4.1 In this guide, two general methods are presented for
A606 Specification for Steel, Sheet and Strip, High-
estimating the atmospheric corrosion resistance of low-alloy
Strength, Low-Alloy, Hot-Rolled and Cold-Rolled, with
weathering steels. These are not alternative methods; each
Improved Atmospheric Corrosion Resistance
methodisintendedforaspecificpurpose,asoutlinedin5.2and
A709/A709M Specification for Structural Steel for Bridges
5.3.
A852/A852M Specification for Quenched and Tempered
4.1.1 The first method utilizes linear regression analysis of
Low-Alloy Structural Steel Plate with 70 ksi [485 MPa]
short-term atmospheric corrosion data to enable prediction of
Minimum Yield Strength to 4 in. [100 mm] Thick (With-
long-term performance by an extrapolation method.
drawn 2010)
4.1.2 Thesecondmethodutilizespredictiveequationsbased
A871/A871M Specification for High-Strength Low-Alloy
on the steel composition to calculate indices of atmospheric
corrosion resistance.
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
5. Significance and Use
Metals and is the direct responsibility of Subcommittee G01.04 on Atmospheric
Corrosion.
5.1 In the past, ASTM specifications for low-alloy weath-
Current edition approved May 1, 2010. Published May 2010. Originally
ering steels, such as Specifications A242/A242M, A588/
approved in 1989. Last previous edition approved in 2004 as G101–04. DOI:
A588M, A606 Type 4, A709/A709M Grade 50W, HPS 70W,
10.1520/G0101-04R10.
and 100W, A852/A852M, and A871/A871M stated that the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
atmospheric corrosion resistance of these steels is “approxi-
Standards volume information, refer to the standard’s Document Summary page on
matelytwotimesthatofcarbonstructuralsteelwithcopper.”A
the ASTM website.
footnote in the specifications stated that “two times carbon
The last approved version of this historical standard is referenced on
www.astm.org. structural steel with copper is equivalent to four times carbon
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G101 − 04 (2010)
Differentiation of Eq 2 with respect to time gives the corrosion rate (R)
structural steel without copper (Cu 0.02 maximum).” Because
at any given time:
such statements relating the corrosion resistance of weathering
~B21!
steels to that of other steels are imprecise and, more
R 5 ABt (3)
Also, the time to a given corrosion loss can be calculated as follows:
importantly,lacksignificancetotheuser (1 and 2) ,thepresent
1/B
guide was prepared to describe more meaningful methods of
t 5 C/A (4)
~ !
estimating the atmospheric corrosion resistance of weathering
6.2.3 Examples of projected atmospheric corrosion losses
steels.
over a period of fifty years for low-alloy weathering steels in
5.2 The first method of this guide is intended for use in
various environments are presented in Appendix X1.
estimating the expected long-term atmospheric corrosion
losses of specific grades of low-alloy steels in various NOTE2—Ithasbeenreported (6 and 7)thatforsomeenvironments,use
of log-log linear regression extrapolations may result in predictions which
environments, utilizing existing short-term atmospheric corro-
aresomewhatlowerorsomewhathigherthanactuallosses.Specifically,in
sion data for these grades of steel.
environments of very low corrosivity, the log-log predictions may be
5.3 The second method of this guide is intended for use in
higher than actual losses (6), whereas in environments of very high
estimating the relative atmospheric corrosion resistance of a corrosivity the opposite may be true (7). For these cases, use of numerical
optimizationorcompositemodelingmethods (7 and 8)mayprovidemore
specific heat of low-alloy steel, based on its chemical compo-
accurate predictions. Nevertheless, the simpler log-log linear regression
sition.
method described above provides adequate estimates for most purposes.
5.4 It is important to recognize that the methods presented
6.3 Predictive Methods Based on Steel Composition—Two
here are based on calculations made from test data for flat,
approaches are provided for prediction of relative corrosion
boldly exposed steel specimens. Atmospheric corrosion rates
resistance from composition. The first is based on the data of
can be much higher when the weathering steel remains wet for
Larrabee and Coburn (6.3.1). Its advantage is that it is
prolonged periods of time, or is heavily contaminated with salt
comparatively simple to apply. This approach is suitable when
or other corrosive chemicals. Therefore, caution must be
the alloying elements are limited to Cu, Ni, Cr, Si, and P, and
exercised in the application of these methods for prediction of
in amounts within the range of the original data. Corrosion
long-term performance of actual structures.
indices by either of the two approaches can be easily deter-
6. Procedure
mined by use of the tool provided on the ASTM website at
http://www.astm.org/COMMIT/G01_G101Calculator.xls.
6.1 Atmospheric corrosion data for the methods presented
here should be collected in accordance with Practice G50. 6.3.1 Predictive Method Based on the Data of Larabee and
Coburn—Equations for predicting corrosion loss of low-alloy
Specimen preparation, cleaning, and evaluation should con-
form to Practice G1. steels after 15.5 years of exposure to various atmospheres,
basedonthechemicalcompositionofthesteel,werepublished
6.2 Linear Regression Extrapolation Method:
by Legault and Leckie (9). The equations are based on
6.2.1 This method essentially involves the extrapolation of
extensive data published by Larrabee and Coburn (10).
logarithmic plots of corrosion losses versus time. Such plots of
6.3.1.1 For use in this guide, the Legault-Leckie equation
atmospheric corrosion data generally fit well to straight lines,
for an industrial atmosphere (Kearny, NJ) was modified to
and can be represented by equations in slope-intercept form,
(3-5): allow calculation of an atmospheric corrosion resistance index
based on chemical composition. The modification consisted of
logC 5 logA1Blogt (1)
deletion of the constant and changing the signs of all the terms
where:
in the equation. The modified equation for calculation of the
C = corrosion loss,
atmospheric corrosion resistance index (I) is given below. The
t = time, and
higher the index, the more corrosion resistant is the steel.
Aand B = constants.Ais the corrosion loss at t = 1, and B is
I 5 26.01 ~%Cu!13.88 ~%Ni!11.20 ~%Cr!
the slope of a log C versus log + plot.
11.49 ~%Si!117.28 ~%P! 2 7.29 ~%Cu!~%Ni!
C may be expressed as mass loss per unit area, or as a
29.10 ~%Ni!~%P! 2 33.39 ~%Cu!
calculated thickness loss or penetration based on mass loss.
NOTE 3—Similar indices can be calculated for the Legault-Leckie
6.2.2 The method is best implemented by linear regression
equations for marine and semi-rural atmospheres. However, it has been
found that the ranking of the indices of various steel compositions is the
analysis, using the method of least squares detailed in Guide
same for all these equations. Therefore, only one equation is required to
G16.At least three data points are required. Once the constants
rank the relative corrosion resistance of different steels.
of the equation are determined by the linear regression
analysis, the projected corrosion loss can be calculated for any
6.3.1.2 Thepredictiveequationshouldbeusedonlyforsteel
given time. A sample calculation is shown in Appendix X1.
compositions within the range of the original test materials in
the Larrabee-Coburn data set (7). These limits are as follows:
NOTE 1—Eq 1 can also be written as follows:
Cu 0.51 % max
B
C 5 At (2)
Ni 1.1 % max
Cr 1.3 % max
4 Si 0.64 % max
The boldface numbers in parentheses refer to a list of references at the end of
this standard. P 0.12 % max
G101 − 04 (2010)
6.3.1.3 Examples of averages and ranges of atmospheric (2) The times for pure iron to reach a 254-µm loss at the
corrosion resistance indices calculated by the Larrabee-Coburn three sites are then calculated by use of Eq 4.
methodfor72heatsofeachoftwoweatheringsteelsareshown
(3) For a given low alloy steel, A and B values at each site
in Table X2.1.
are calculated from the regression constants and coefficients in
6.3.2 Predictive Method Based on the Data of Townsend—
Table 1, and Eq 5 and 6.
Equations for predicting the corrosion loss of low alloy steels
(4) The losses of the low alloy steel at each site are
based on a statistical analysis of the effects of chemical
calculated from Eq 1 at the times required for pure iron to lose
composition on the corrosion losses of hundreds of steels
254 µm at the same site as determined in (1).
exposed at three industrial locations were published by
(5) The respective differences between the 254-µm loss for
Townsend (11).
pure iron and the calculated loss for the low alloy steel at each
6.3.2.1 In this method, the coefficients A and B, as defined
siteasdeterminedin (4)areaveragedtogiveacorrosionindex.
for Eq 1, are calculated as linear combinations of the effects of
(6) Examples of corrosion indices calculated by the
each alloying element, according to Eq 5 and 6.
Townsend method are shown in Table 2 for pure iron and a
A 5 a 1Σa x (5)
variety of low-alloy steel compositions. The upper limit of the
o i i
composition ranges of each element in the Townsend data are
B 5 b 1Σb x (6)
o i i
also given in Table 2.
where:
6.3.3 Theminimumacceptableatmosphericcorrosionindex
A and B = constants in the exponential corrosion loss func-
should be a matter of negotiation between the buyer and the
tion as defined for Eq 1,
seller.
a and b = constants for three industrial locations as given
o o
in Table 1,
7. Report
a and b = constants for each alloying element as given in
i i
7.1 When reporting estimates of atmospheric corrosion
Table 1 for three industrial locations, and
resistance, the method of calculation should always be speci-
x = compositions of the individual alloying
i
fied.Also,intheLinearRegressionExtrapolationMethod(6.2)
elements.
of this guide, the data used should be referenced with respect
TheAand B values calculated from Eq 4 and 5 can be used
to type of specimens, condition and location of exposure, and
to compute corrosion losses, corrosion rates, and times to a
duration of exposure.
given loss at any of the three sites by use of Eq 2-4,
respectively.
8. Keywords
6.3.2.2 For purposes of calculating a corrosion index from
8.1 atmospheric corrosion resistance; compositional effects;
the Townsend data, the following procedure shall be followed.
(1) For each of the three test sites, A and B values for pure, corrosion indices; high-strength; low-alloy steel; industrial
environments; marine environments; rural environments;
unalloyed iron at are calculated by use of the regression
constants given in Table 1, and Eq 5 and 6. weathering steels
TABLE 1 Constants and Coefficients for Calculating the Rate Constants A and B from Composition
A (µm) B (T in months)
n 275 227 248 275 227 248
site Bethlehem, PA Columbus, OH Pittsburgh, PA Bethlehem, PA Columbus, OH Pittsburgh, PA
Constant 15.157 16.143 14.862 0.511 0.539 0.604
A
Carbon 6.310 3.350 –0.102 –0.103 –0.046
A
Manganese –2.170 –2.370 –0.097 –0.019 0.042
Phosphorus –1.770 –10.250 –5.120 –0.592 –0.333 –0.546
A
Sulfur –27.200 –15.970 2.408 0.908 1.004
Silicon 6.50 2.96 1.38 –0.20 –0.16 –0.13
Nickel 1.970 –1.380 1.180 –0.080 –0.029 –0.088
A
Chromium 2.560 2.370 –0.103 –0.095 –0.174
A
Copper 0.990 –1.970 –0.072 –0.067 –0.068
A AA
Aluminum 1.580 5.520 –0.087
A AA A
Vanadium 6.110 –0.193
Cobalt 1.580 –1.770 –2.560 –0.063 –0.053 0.044
A
Arsenic 3.150 –6.110 –7.690 –0.157 0.097
AA A
Molybdenum –2.960 –0.078 –0.038
A
Tin –3.740 –7.490 –9.860 –0.151 –0.038
A A AA
Tungsten –5.520 –0.148
A
Coefficient has greater than 50 % probability of chance occurrence.
G101 − 04 (2010)
A
TABLE 2 Corrosion Indices for Pure Iron and Various Low-Alloy Steels
Element Range Pure Fe Typical A36 + Min. Alloy 1 Typical Alloy 2 Max. Alloy 3 Alloy 4
w/o Maximum A36 0.2% Cu A588 A588 A588
C 1.50 0.000 0.160 0.160 0.060 0.075 0.100 0.060 0.190 0.091 0.060
Mn 1.50 0.000 1.010 1.010 0.800 0.690 1.180 1.090 1.250 0.580 1.000
P 0.30 0.000 0.012 0.012 0.005 0.030 0.012 0.007 0.040 0.004 0.010
S 0.30 0.000 0.013 0.013 0.001 0.004 0.011 0.002 0.050 0.001 0.002
Si 1.50 0.000 0.220 0.220 0.300 0.280 0.360 0.290 0.650 0.200 0.250
Ni 1.10 0.000 0.01
...
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