ASTM G101-04(2020)

Standard Guide for Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels

SIGNIFICANCE AND USE
5.1 In the past, ASTM specifications for low-alloy weathering steels, such as Specifications A242/A242M, A588/A588M, A606/A606M 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),4 the present guide was prepared to describe more meaningful methods of estimating the atmospheric corrosion resistance of weathering steels.  
5.2 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.  
5.3 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.  
5.4 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/A606M 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.  
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 77.060 - Corrosion of metals
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.04 - Corrosion of Metals in Natural Atmospheric and Aqueous Environments

Relations

• Refers: ASTM A242/A242M-24 - Standard Specification for High-Strength Low-Alloy Structural Steel
• Effective Date: 01-Mar-2024
• Refers: ASTM G16-13(2019) - Standard Guide for Applying Statistics to Analysis of Corrosion Data
• Effective Date: 15-Feb-2019
• Refers: ASTM A709/A709M-17 - Standard Specification for Structural Steel for Bridges
• Effective Date: 01-Sep-2017
• Refers: ASTM A709/A709M-17e1 - Standard Specification for Structural Steel for Bridges
• Effective Date: 01-Sep-2017
• Refers: ASTM A709/A709M-16a - Standard Specification for Structural Steel for Bridges
• Effective Date: 01-May-2016
• Refers: ASTM A709/A709M-16 - Standard Specification for Structural Steel for Bridges
• Effective Date: 15-Feb-2016
• Refers: ASTM A606/A606M-15 - Standard Specification for Steel, Sheet and Strip, High-Strength, Low-Alloy, Hot-Rolled and Cold-Rolled, with Improved Atmospheric Corrosion Resistance
• Effective Date: 01-Nov-2015
• Refers: ASTM A871/A871M-14 - Standard Specification for High-Strength Low-Alloy Structural Steel Plate With Atmospheric Corrosion Resistance
• Effective Date: 01-May-2014
• Refers: ASTM G16-13 - Standard Guide for Applying Statistics to Analysis of Corrosion Data
• Effective Date: 01-Dec-2013
• Refers: ASTM A709/A709M-13a - Standard Specification for Structural Steel for Bridges
• Effective Date: 01-Oct-2013
• Refers: ASTM A242/A242M-13 - Standard Specification for High-Strength Low-Alloy Structural Steel
• Effective Date: 01-May-2013
• Refers: ASTM A709/A709M-13 - Standard Specification for Structural Steel for Bridges
• Effective Date: 01-May-2013
• Refers: ASTM A871/A871M-12 - Standard Specification for High-Strength Low-Alloy Structural Steel Plate With Atmospheric Corrosion Resistance
• Effective Date: 01-May-2012
• Refers: ASTM G1-03(2011) - Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• Effective Date: 01-Dec-2011
• Refers: ASTM A709/A709M-11 - Standard Specification for Structural Steel for Bridges
• Effective Date: 01-May-2011

Overview

ASTM G101-04(2020) - Standard Guide for Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels provides established methods for estimating how low-alloy weathering steels perform when exposed to atmospheric conditions. Developed by ASTM International, this guide is essential for steel manufacturers, engineers, designers, and asset owners who need to predict the long-term durability and service life of low-alloy steels such as those specified in ASTM A242/A242M, A588/A588M, A606/A606M, A709/A709M, A852/A852M, and A871/A871M. The standard emphasizes using meaningful predictive approaches rather than relying on broad, imprecise equivalency statements when describing the atmospheric corrosion resistance of weathering steels.

Key Topics

• Estimation Methods: The guide presents two main methods:
  • Long-Term Loss Estimation: Allows users to estimate expected steel thickness loss from atmospheric corrosion over extended periods, utilizing results from short-term exposure tests.
  • Composition-Based Resistance Index: Enables calculation of the relative corrosion resistance of a particular steel “heat” using its chemical composition.
• Applicability: Based on data from flat, boldly exposed steel surfaces; acknowledges that corrosion rates can be significantly higher with prolonged wetness or salt contamination.
• Scope of Steels Covered: Focuses on high-strength, low-alloy weathering steels recognized for their improved atmospheric corrosion resistance.
• Reporting Requirements: When reporting corrosion resistance estimates, the calculation method as well as specifics about the exposure test data must be clearly stated.
• Units of Measurement: All values are stated in SI units for international consistency.

Applications

This ASTM corrosion standard provides practical value in several fields, especially where atmospheric corrosion resistance is critical to structural integrity and lifecycle costs. Key applications include:

• Bridge and Infrastructure Design: When specifying weathering steels for bridges, highways, and buildings, engineers use the standard to estimate maintenance intervals and predict service life.
• Material Selection: Steel producers and buyers rely on the guide to compare corrosion resistance among different grades or heats of low-alloy steels before procurement for outdoor applications.
• Corrosion Testing and Research: Laboratories conducting atmospheric exposure tests or research on corrosion performance apply the methodologies for data analysis and reporting.
• Asset Management: Facility owners use predictive corrosion indices to make informed decisions regarding inspection, maintenance, and the selection of protective coatings or surface treatments.

Related Standards

Standards referenced and complementary to ASTM G101 include:

• ASTM A242/A242M: Specification for high-strength low-alloy structural steel with improved atmospheric corrosion resistance.
• ASTM A588/A588M: Covers high-strength low-alloy structural steel up to 50 ksi yield strength.
• ASTM A606/A606M: Hot-rolled and cold-rolled weathering steel for sheet and strip.
• ASTM A709/A709M: Structural steel for bridge applications, including various grades with weathering properties.
• ASTM A871/A871M, A852/A852M: High-strength low-alloy structural steels with atmospheric corrosion resistance.
• ASTM G1: Practice for preparing, cleaning, and evaluating corrosion test specimens.
• ASTM G16: Guide for applying statistics in the analysis of corrosion data.
• ASTM G50: Practice for conducting atmospheric corrosion tests on metals.

Conclusion

Adhering to ASTM G101-04(2020) ensures a standardized, data-driven approach to estimating the atmospheric corrosion resistance of low-alloy steels used in critical structures and exposed environments. By applying the detailed methods offered in the guide, stakeholders can achieve greater accuracy in durability forecasts, optimize material selection, and support the long-term performance of their steel assets. For best results, use this guide alongside related ASTM standards relevant to specific steel grades and atmospheric testing practices.

Keywords: atmospheric corrosion resistance, low-alloy weathering steel, corrosion index, predictive corrosion assessment, ASTM standards, steel durability, infrastructure corrosion testing, steel composition analysis.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G101 − 04 (Reapproved 2020)
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 Low-Alloy Structural Steel Plate with 70 ksi [485 MPa]
Minimum Yield Strength to 4 in. [100 mm] Thick (With-
1.1 This guide presents two methods for estimating the
drawn 2010)
atmospheric corrosion resistance of low-alloy weathering
A871/A871M Specification for High-Strength Low-Alloy
steels, such as those described in Specifications A242/A242M,
Structural Steel Plate With Atmospheric Corrosion Resis-
A588/A588M, A606/A606M Type 4, A709/A709M grades
tance
50W, HPS 70W, and 100W, A852/A852M, and A871/A871M.
G1 Practice for Preparing, Cleaning, and Evaluating Corro-
One method gives an estimate of the long-term thickness loss
sion Test Specimens
of a steel at a specific site based on results of short-term tests.
G16 Guide for Applying Statistics to Analysis of Corrosion
The other gives an estimate of relative corrosion resistance
Data
based on chemical composition.
G50 Practice for Conducting Atmospheric Corrosion Tests
1.2 The values stated in SI units are to be regarded as
on Metals
standard. No other units of measurement are included in this
3. Terminology
standard.
1.3 This international standard was developed in accor- 3.1 Definitions of Terms Specific to This Standard:
dance with internationally recognized principles on standard- 3.1.1 low-alloy steels—iron-carbon alloys containing
ization established in the Decision on Principles for the greater than 1.0 % but less than 5.0 %, by mass, total alloying
Development of International Standards, Guides and Recom- elements.
mendations issued by the World Trade Organization Technical 3.1.1.1 Discussion—Most “low-alloy weathering steels”
Barriers to Trade (TBT) Committee. contain additions of both chromium and copper, and may also
contain additions of silicon, nickel, phosphorus, or other
2. Referenced Documents
alloying elements which enhance atmospheric corrosion resis-
tance.
2.1 ASTM Standards:
A242/A242M Specification for High-Strength Low-Alloy
4. Summary of Guide
Structural Steel
4.1 In this guide, two general methods are presented for
A588/A588M Specification for High-Strength Low-Alloy
estimating the atmospheric corrosion resistance of low-alloy
Structural Steel, up to 50 ksi [345 MPa] Minimum Yield
weathering steels. These are not alternative methods; each
Point, with Atmospheric Corrosion Resistance
methodisintendedforaspecificpurpose,asoutlinedin5.2and
A606/A606M Specification for Steel, Sheet and Strip, High-
5.3.
Strength, Low-Alloy, Hot-Rolled and Cold-Rolled, with
4.1.1 The first method utilizes linear regression analysis of
Improved Atmospheric Corrosion Resistance
short-term atmospheric corrosion data to enable prediction of
A709/A709M Specification for Structural Steel for Bridges
long-term performance by an extrapolation method.
A852/A852M Specification for Quenched and Tempered
4.1.2 Thesecondmethodutilizespredictiveequationsbased
on the steel composition to calculate indices of atmospheric
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
corrosion resistance.
Metals and is the direct responsibility of Subcommittee G01.04 on Corrosion of
Metals in Natural Atmospheric and Aqueous Environments.
5. Significance and Use
Current edition approved Nov. 1, 2020. Published November 2020. Originally
5.1 In the past, ASTM specifications for low-alloy weath-
approvedin1989.Lastpreviouseditionapprovedin2015asG101–04(2015).DOI:
10.1520/G0101-04R20.
ering steels, such as Specifications A242/A242M, A588/
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G101 − 04 (2020)
A588M, A606/A606M Type 4, A709/A709M Grade 50W, of the equation are determined by the linear regression
HPS 70W, and 100W, A852/A852M, and A871/A871M stated analysis, the projected corrosion loss can be calculated for any
that the atmospheric corrosion resistance of these steels is given time. A sample calculation is shown in Appendix X1.
“approximately two times that of carbon structural steel with
NOTE 1—Eq 1 can also be written as follows:
copper.”Afootnote in the specifications stated that “two times
B
C 5 At (2)
carbon structural steel with copper is equivalent to four times
Differentiation of Eq 2 with respect to time gives the corrosion rate (R)
carbon structural steel without copper (Cu 0.02 maximum).”
at any given time:
Because such statements relating the corrosion resistance of
B21
~ !
R 5 ABt (3)
weatheringsteelstothatofothersteelsareimpreciseand,more
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
NOTE2—Ithasbeenreported (6 and 7)thatforsomeenvironments,use
losses of specific grades of low-alloy steels in various
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
higher than actual losses (6), whereas in environments of very high
5.3 The second method of this guide is intended for use in
corrosivity the opposite may be true (7). For these cases, use of numerical
estimating the relative atmospheric corrosion resistance of a
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
method described above provides adequate estimates for most purposes.
sition.
6.3 Predictive Methods Based on Steel Composition—Two
5.4 It is important to recognize that the methods presented
approaches are provided for prediction of relative corrosion
here are based on calculations made from test data for flat,
resistance from composition. The first is based on the data of
boldly exposed steel specimens. Atmospheric corrosion rates
Larrabee and Coburn (6.3.1). Its advantage is that it is
can be much higher when the weathering steel remains wet for
comparatively simple to apply. This approach is suitable when
prolonged periods of time, or is heavily contaminated with salt
the alloying elements are limited to Cu, Ni, Cr, Si, and P, and
or other corrosive chemicals. Therefore, caution must be
in amounts within the range of the original data. Corrosion
exercised in the application of these methods for prediction of
indices by either of the two approaches can be easily deter-
long-term performance of actual structures.
mined by use of the tool provided on the ASTM website at
6. Procedure
http://www.astm.org/COMMIT/G01_G101Calculator.xls.
6.3.1 Predictive Method Based on the Data of Larabee and
6.1 Atmospheric corrosion data for the methods presented
Coburn—Equations for predicting corrosion loss of low-alloy
here should be collected in accordance with Practice G50.
steels after 15.5 years of exposure to various atmospheres,
Specimen preparation, cleaning, and evaluation should con-
basedonthechemicalcompositionofthesteel,werepublished
form to Practice G1.
by Legault and Leckie (9). The equations are based on
6.2 Linear Regression Extrapolation Method:
extensive data published by Larrabee and Coburn (10).
6.2.1 This method essentially involves the extrapolation of
6.3.1.1 For use in this guide, the Legault-Leckie equation
logarithmic plots of corrosion losses versus time. Such plots of
for an industrial atmosphere (Kearny, NJ) was modified to
atmospheric corrosion data generally fit well to straight lines,
allow calculation of an atmospheric corrosion resistance index
and can be represented by equations in slope-intercept form,
based on chemical composition. The modification consisted of
(3-5):
deletion of the constant and changing the signs of all the terms
logC 5 logA1Blogt (1)
in the equation. The modified equation for calculation of the
atmospheric corrosion resistance index (I) is given below. The
where:
higher the index, the more corrosion resistant is the steel.
C = corrosion loss,
t = time, and I 5 26.01 ~%Cu!13.88 ~%Ni!11.20 ~%Cr!
A and B = constants. A is the corrosion loss at t = 1, and B 11.49 ~%Si!117.28 ~%P! 2 7.29 ~%Cu!~%Ni!
29.10 %Ni %P 2 33.39 %Cu
is the slope of a log C versus log + plot. ~ !~ ! ~ !
NOTE 3—Similar indices can be calculated for the Legault-Leckie
C may be expressed as mass loss per unit area, or as a
equations for marine and semi-rural atmospheres. However, it has been
calculated thickness loss or penetration based on mass loss.
found that the ranking of the indices of various steel compositions is the
6.2.2 The method is best implemented by linear regression
same for all these equations. Therefore, only one equation is required to
rank the relative corrosion resistance of different steels.
analysis, using the method of least squares detailed in Guide
G16.At least three data points are required. Once the constants
6.3.1.2 Thepredictiveequationshouldbeusedonlyforsteel
compositions within the range of the original test materials in
the Larrabee-Coburn data set (7). These limits are as follows:
The boldface numbers in parentheses refer to a list of references at the end of
this standard. Cu 0.51 % max
G101 − 04 (2020)
Ni 1.1 % max (2) The times for pure iron to reach a 254 µm loss at the
Cr 1.3 % max three sites are then calculated by use of Eq 4.
Si 0.64 % max
(3) For a given low alloy steel,Aand B values at each site
P 0.12 % max
are calculated from the regression constants and coefficients in
6.3.1.3 Examples of averages and ranges of atmospheric
Table 1, and Eq 5 and 6.
corrosion resistance indices calculated by the Larrabee-Coburn
(4) The losses of the low alloy steel at each site are
methodfor72heatsofeachoftwoweatheringsteelsareshown
calculated from Eq 1 at the times required for pure iron to lose
in Table X2.1.
254 µm at the same site as determined in (1).
6.3.2 Predictive Method Based on the Data of Townsend—
(5) The respective differences between the 254 µm loss for
Equations for predicting the corrosion loss of low alloy steels
pure iron and the calculated loss for the low alloy steel at each
based on a statistical analysis of the effects of chemical
siteasdeterminedin (4)areaveragedtogiveacorrosionindex.
composition on the corrosion losses of hundreds of steels
(6) Examples of corrosion indices calculated by the
exposed at three industrial locations were published by
Townsend method are shown in Table 2 for pure iron and a
Townsend (11).
variety of low-alloy steel compositions. The upper limit of the
6.3.2.1 In this method, the coefficients A and B, as defined
composition ranges of each element in the Townsend data are
for Eq 1, are calculated as linear combinations of the effects of
also given in Table 2.
each alloying element, according to Eq 5 and 6.
6.3.3 Theminimumacceptableatmosphericcorrosionindex
A 5 a 1Σa x (5)
o i i
should be a matter of negotiation between the buyer and the
B 5 b 1Σb x (6)
o i i
seller.
where:
7. Report
A and B = constants in the exponential corrosion loss func-
tion as defined for Eq 1,
7.1 When reporting estimates of atmospheric corrosion
a and b = constantsforthreeindustriallocationsasgivenin
o o
resistance, the method of calculation should always be speci-
Table 1,
fied.Also,intheLinearRegressionExtrapolationMethod(6.2)
aand b = constants for each alloying element as given in
i i
of this guide, the data used should be referenced with respect
Table 1 for three industrial locations, and
to type of specimens, condition and location of exposure, and
x = compositionsoftheindividualalloyingelements.
i
duration of exposure.
TheAand B values calculated from Eq 4 and 5 can be used
to compute corrosion losses, corrosion rates, and times to a
8. Keywords
given loss at any of the three sites by use of Eq 2-4,
8.1 atmospheric corrosion resistance; compositional effects;
respectively.
corrosion indices; high-strength; industrial environments; low-
6.3.2.2 For purposes of calculating a corrosion index from
the Townsend data, the following procedure shall be followed. alloy steel; marine environments; rural environments; weath-
(1) Foreachofthethreetestsites,AandBvaluesforpure, ering steels
unalloyed iron at are calcula
...