ASTM G101-97

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Designation: G 101 – 97
Standard Guide for
Estimating the Atmospheric Corrosion Resistance of Low-
Alloy Steels
This standard is issued under the fixed designation G 101; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope G 50 Practice for Conducting Atmospheric Corrosion Tests
on Metals
1.1 This guide presents two methods for estimating the
atmospheric corrosic resistance of low-alloy weathering steels,
3. Terminology
such as those described in Specifications A 242/A 242M,
3.1 Definitions of Terms Specific to This Standard:
A 588/A 588M, A 606 Type 4, A 709/A 709M grades 50W,
3.1.1 low-alloy steels—Iron-carbon alloys containing
70W, and 100W, A 852, and A871. One method gives an
greater than 1.0 % but less than 5.0 %, by mass, total alloying
estimate of the long term thickness loss of a steel at a specific
elements.
site based on results of short-term tests. The other gives an
estimate of relative corrosion resistance based on chemical
NOTE 1—Most “low-alloy weathering steels” contain additions of both
composition. chromium and copper, and may also contain additions of silicon, nickel,
phosphorus, or other alloying elements which enhance atmospheric
2. Referenced Documents corrosion resistance.
2.1 ASTM Standards:
4. Summary of Guide
A 242/A 242M Specification for High-Strength Low-Alloy
2 4.1 In this guide, two general methods are presented for
Structural Steel
estimating the atmospheric corrosion resistance of low-alloy
A 588/A 588M Specification for High-Strength Low-Alloy
weathering steels. These are not alternative methods; each
Structural Steel with 50 Ksi (345 MPa) Minimum Yield
2 method is intended for a specific purpose, as outlined in 5.2 and
Point to 4 in. (100 mm) Thick
5.3.
A 606 Specification for Steel, Sheet and Strip, High
4.1.1 The first method utilizes linear regression analysis of
Strength, Low-Alloy, Hot-Rolled and Cold Rolled, With
short-term atmospheric corrosion data to enable prediction of
Improved Atmospheric Corrosion Resistance
long-term performance by an extrapolation method.
A 709/A 709M Specification for Carbon and High-Strength
4.1.2 The second method utilizes predictive equations based
Low-Alloy Structural Steel Shapes, Plates, and Bars and
on the steel composition to calculate indices of atmospheric
Quenched-and-Tempered Alloy Structural Steel Plates for
corrosion resistance.
Bridges
A 852/A 852M Specification for Quenched and Tempered
5. Significance and Use
Low-Alloy Structural Steel Plate with 70 ksi (485 MPa)
2 5.1 In the past, ASTM specifications for low-alloy weath-
Minimum Yield Strength to 4 in (100 mm) Thick
ering steels, such as Specifications A 242/A 242M, A 588/
A 871/A 871M Specification for High Strength Low-Alloy
A 588M, A 606 Type 4, A 709/A 709M Grade 50W, 70W, and
Structural Steel Plate With Atmopheric Corrosion Resis-
2 100W, A 852, and A 871 stated that the atmospheric corrosion
tance
resistance of these steels is “approximately two times that of
G 1 Practice for Preparing, Cleaning, and Evaluating Cor-
4 carbon structural steel with copper.” A footnote in the specifi-
rosion Test Specimens
cations stated that “two times carbon structural steel with
G 16 Guide for Applying Statistics to Analysis of Corrosion
4 copper is equivalent to four times carbon structural steel
Data
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 signifi-
cance to the user (1 and 2) , the present guide was prepared to
This guide is under the jurisdiction of ASTM Committee G-1 on Corrosion of
Metals and is the direct responsibility of Subcommittee G01.04on Atmospheric
describe more meaningful methods of estimating the atmo-
Corrosion.
spheric corrosion resistance of weathering steels.
Current edition approved April 10, 1997. Published July 1997. Originally
published as G 101 – 89. Last previous edition G 101 – 94.
Annual Book of ASTM Standards, Vol 01.04.
Annual Book of ASTM Standards, Vol 01.03.
The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 03.02.
this guide.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
G 101
5.2 The first method of this guide is intended for use in are somewhat lower or somewhat higher than actual losses. Specifically, in
environments of very low corrosivity, the log-log predictions may be
estimating the expected long-term atmospheric corrosion
higher than actual losses (6), whereas in environments of very high
losses of specific grades of low-alloy steels in various envi-
corrosivity the opposite may be true (7). For these cases, use of numerical
ronments, utilizing existing short-term atmospheric corrosion
optimization or composite modeling methods (7 and 8) may provide more
data for these grades of steel.
accurate predictions. Nevertheless, the simpler log-log linear regression
5.3 The second method of this guide is intended for use in
method described above provides adequate estimates for most purposes.
estimating the relative atmospheric corrosion resistance of a
6.3 Predictive Method Based on Steel Composition:
specific heat of low-alloy steel, based on its chemical compo-
6.3.1 Equations for predicting corrosion loss of low-alloy
sition.
steels after 15.5 years of exposure to various atmospheres,
5.4 It is important to recognize that the methods presented
based on the chemical composition of the steel, were published
here are based on calculations made from test data for flat,
by Legault and Leckie (9). The equations are based on
boldly exposed steel specimens. Atmospheric corrosion rates
extensive data published by Larrabee and Coburn (10).
can be much higher when the weathering steel remains wet for
6.3.2 For use in this guide, the Legault-Leckie equation for
prolonged periods of time, or is heavily contaminated with salt
an industrial atmosphere (Kearny, N.J.) was modified to allow
or other corrosive chemicals. Therefore, caution must be
calculation of an atmospheric corrosion resistance index based
exercised in the application of these methods for prediction of
on chemical composition. The modification consisted of dele-
long-term performance of actual structures.
tion of the constant and changing the signs of all the terms in
the equation. The modified equation for calculation of the
6. Procedure
atmospheric corrosion resistance index (I) is given below. The
6.1 Atmospheric corrosion data for the methods presented
higher the index, the more corrosion resistant is the steel.
here should be collected in accordance with Practice G 50.
I 5 26.01 ~% Cu! 1 3.88 ~% Ni! 1 1.20 ~% Cr!
Specimen preparation, cleaning, and evaluation should con-
1 1.49 ~% Si! 1 17.28 ~% P! 2 7.29 ~% Cu!
form to Practice G 1.
~% Ni! 2 9.10 ~% Ni! ~% P! 2 33.39 ~% Cu!
6.2 Linear Regression Extrapolation Method:
6.2.1 This method essentially involves the extrapolation of
NOTE 4—Similar indices can be calculated for the Legault-Leckie
logarithmic plots of corrosion losses versus time. Such plots of
equations for marine and semi-rural atmospheres. However, it has been
atmospheric corrosion data generally fit well to straight lines, found that the ranking of the indices of various steel compositions is the
same for all these equations. Therefore, only one equation is required to
and can be represented by equations in slope-intercept form,
rank the relative corrosion resistance of different steels.
(3-5):
6.3.3 The predictive equation should be used only for steel
log C 5 log A 1 B log t (1)
compositions within the range of the original test materials in
where:
the Larrabee-Coburn data set (7). These limits are as follows:
C 5 corrosion loss,
Cu 0.51 % max
t 5 time, and
Ni 1.1 % max
A and B 5 constants. A is the corrosion loss at t 5 1, and B
Cr 1.3 % max
is the slope of a log C versus log + plot.
Si 0.64 % max
C may be expressed as mass loss per unit area, or as a
P 0.12 % max
calculated thickness loss or penetration based on mass loss.
6.3.4 Examples of averages and ranges of atmospheric
6.2.2 The method is best implemented by linear regression
corrosion resistance indices calculated for 72 heats of each of
analysis, using the method of least squares detailed in Guide
two weathering steels are shown in Table X2.1.
G 16. At least three data points are required. Once the constants
6.3.5 The minimum acceptable atmospheric corrosion index
of the equation are determined by the linear regression analy-
should be a matter of negotiation between the buyer and the
sis, the projected corrosion loss can be calculated for any given
seller.
time. A sample calculation is shown in Appendix X1.
NOTE 2—Eq 1 can also be written as follows: 7. Report
B
7.1 When reporting estimates of atmospheric corrosion
C 5 At (2)
Differentiation of Eq 2 with respect to time gives the corrosion rate (R) resistance, the method of calculation should always be speci-
at any given time:
fied. Also, in the Linear Regression Extrapolation Method (6.2)
~B 2 1! of this guide, the data used should be referenced with respect
R 5 ABt (3)
to type of specimens, condition and location of exposure, and
Also, the time to a given corrosion loss can be calculated as follows:
duration of exposure.
1/B
t 5 C/A! (4)
~
6.2.3 Examples of projected atmospheric corrosion losses 8. Keywords
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