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Standard
Test Method
Laboratory Testing of Metals for Resistance to Sulfide
Stress Cracking and Stress Corrosion Cracking in H2S
Environments
This NACE International standard represents a consensus of those individual members who have
reviewed this document, its scope, and provisions. Its acceptance does not in any respect
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marketing, purchasing, or using products, processes, or procedures not in conformance with this
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liability for infringement of Letters Patent. This standard represents minimum requirements and
should in no way be interpreted as a restriction on the use of better procedures or materials.
Neither is this standard intended to apply in all cases relating to the subject. Unpredictable
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Revised 2005-12-03
Revised 1996
Revised 1990
Revised 1986
Approved in 1977
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© 2005, NACE International
NACE Standard TM0177-2005
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TM0177-2005
NACE International i
________________________________________________________________________
Foreword
This standard addresses the testing of metals for resistance to cracking failure under the
combined action of tensile stress and corrosion in aqueous environments containing hydrogen
sulfide (H2S). This phenomenon is generally termed sulfide stress cracking (SSC) when operating
at room temperature and stress corrosion cracking (SCC) when operating at higher temperatures.
In recognition of the variation with temperature and with different materials this phenomenon is
herein called environmental cracking (EC). For the purposes of this standard, EC includes only
SSC, SCC, and hydrogen stress cracking (HSC).
The primary purpose of this standard is to facilitate conformity in testing so that data from different
sources can be compared on a common basis. Consequently, this standard aids the evaluation
and selection of all types of metals and alloys, regardless of their form or application, for service in
H2S environments. This standard contains methods for testing metals using tensile, bent-beam,
C-ring, and double-cantilever-beam (DCB) test specimens. Certain ASTM(1) standard test
methods have been listed as references for supplementary tests, creating a comprehensive test
method standard. In addition, the four-point bent-beam test method is also referenced as a
supplementary test.1,2 This standard is intended for use by laboratory and materials personnel to
facilitate conformity in testing.
SSC of metals exposed to oilfield environments containing H2S was recognized as a materials
failure problem by 1952. Laboratory data and field experience have demonstrated that even
extremely low concentrations of H2S may be sufficient to lead to SSC failure of susceptible
materials. In some cases H2S can act synergistically with chlorides to produce corrosion and
cracking (SSC and other mode) failures. However, laboratory and operating experiences have
also indicated to materials engineers the optimum selection and specification of materials having
minimum susceptibility to SSC. This standard covers test methods for SSC (at room temperature)
and SCC (at elevated temperature), but other failure modes (e.g., hydrogen blistering, hydrogen-
induced cracking [HIC], chloride stress corrosion cracking [SCC], pitting corrosion, and mass-loss
corrosion) must also be considered when selecting materials for use in sour (H2S-containing)
environments.
The need for better understanding of the variables involved in EC of metals in oilfield environments
and better correlation of data has become apparent for several reasons. New design requirements
by the oil and gas production industries call for higher-strength materials that, in general, are more
susceptible to EC than lower-strength alloys. These design requirements have resulted in
extensive development programs to obtain more resistant alloys and/or better heat treatments. At
the same time, users in the petroleum refining and synthetic fuels industries are pushing present
materials much closer to their mechanical limits.
Room-temperature (SSC) failures in some alloys generally are believed to result from hydrogen
embrittlement (HE). When hydrogen is cathodically evolved on the surface of a metal (as by
corrosion or cathodic charging), the presence of H2S (and other compounds, such as those
containing cyanides and arsenic) tends to cause hydrogen atoms to enter the metal rather than to
form hydrogen molecules that cannot enter the metal. In the metal, hydrogen atoms diffuse to
regions of high triaxial tensile stress or to some microstructural configurations where they become
trapped and decrease the ductility of the metal. Although there are several kinds of cracking
damage that can occur in metals, delayed brittle fracture of metals resulting from the combined
action of corrosion in an aqueous sulfide environment and tensile stresses (failure may occur at
stresses far below the yield stress) is the phenomenon known as SSC.
In some cases, however, failure may be the result of localized anodic corrosion processes that
may or may not involve hydrogen. In such instances failure is the result of anodic stress corrosion
cracking (SCC). Such failures have historically been termed SSC even though their cause may
not be hydrogen.
_________________
(1) ASTM International (ASTM), 100 Barr Harbor Dr., West Conshohocken, PA 19428-2959.
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1. General......................................................................................................................... 1
2. EC Testing Variability ................................................................................................... 1
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ii NACE International
3. Reagents ...................................................................................................................... 2
4. Test Specimens and Material Properties ..................................................................... 2
5. Test Vessels and Fixtures ............................................................................................ 3
6. Test Solutions............................................................................................................... 3
7. Testing at Elevated Temperature/Pressure ................................................................. 4
8. Method A—NACE Standard Tensile Test .................................................................... 7
9. Method B—NACE Standard Bent-Beam Test............................................................ 13
10. Method C—NACE Standard C-Ring Test .................................................................. 20
11. Method D—NACE Standard DCB Test ...................................................................... 26
References........................................................................................................................ 37
Appendix A—Safety Considerations in Handling H2S Toxicity ......................................... 37
Appendix B—Explanatory Notes on EC Test Method....................................................... 38
FIGURE 1:Schematic Arrangement of Test Equipment for Method A—NACE Standard
Tensile Test................................................................................................................... 5
FIGURE 2: Schematic Arrangement of Test Equipment for Method B—NACE Standard
Bent-Beam Test, Method C—NACE Standard C-Ring Test, and Method D—NACE
Standard Double-Cantilever Beam Test ....................................................................... 6
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TM0177-2005
This standard was originally published in 1977 by NACE International Task Group T-1F-9, a
component of Unit Committee T-1F on Metallurgy of Oilfield Equipment. The standard was revised
in 1986, 1990, and 1996 by Task Group T-1F-9. It was revised in 2005 by Task Group (TG) 085
on Sulfide Corrosion Cracking: Metallic Materials Testing Techniques. TG 085 is administered by
Specific Technology Group (STG) 32 on Oil and Gas Production—Metallurgy and is sponsored by
STG 62 on Corrosion Monitoring and Measurement—Science and Engineering Applications. The
standard is issued by NACE under the auspices of STG 32.
In NACE standards, the terms shall, must, should, and may are used in accordance with the
definitions of these terms in the NACE Publications Style Manual, 4th ed., Paragraph 7.4.1.9. Shall
and must are used to state mandatory requirements. The term should is used to state something
considered good and is recommended but is not mandatory. The term may is used to state
something considered optional.
________________________________________________________________________
NACE International
Standard
Test Method
Laboratory Testing of Metals for Resistance to Sulfide Stress
Cracking and Stress Corrosion Cracking in H2S Environments
Contents
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TM0177-2005
NACE International iii
FIGURE 3: Tensile Test Specimens................................................................................... 8
FIGURE 4: Constant-Load (Dead-Weight) Device ........................................................... 10
FIGURE 5: Sustained-Load Devices ................................................................................ 11
FIGURE 6: Applied Stress vs. Log (Time-to-Failure)........................................................ 16
FIGURE 7: Dimensional Drawing of the Standard Bent-Beam Test Specimen ............... 17
FIGURE 8: Typical Stressing Fixture for Bent-Beam Test Specimen .............................. 18
FIGURE 9: Dimensional Drawing of the C-Ring Test Specimen...................................... 24
FIGURE 10: DCB Specimen............................................................................................. 30
Table 1—NACE Uniform Material Testing Report Form (Part 1): Testing in Accordance
with NACE Standard TM0177 Method A—NACE Standard Tensile Test................... 14
Table 1—NACE Uniform Material Testing Report Form (Part 2): Testing in Accordance
with NACE Standard TM0177 Method A—NACE Standard Tensile Test................... 15
Table 2—NACE Uniform Material Testing Report Form (Part 1): Testing in Accordance
with NACE Standard TM0177 Method B—NACE Standard Bent-Beam Test ............ 22
Table 2—NACE Uniform Material Testing Report Form (Part 2): Testing in Accordance
with NACE Standard TM0177 Method B—NACE Standard Bent-Beam Test ............ 23
Table 3—NACE Uniform Material Testing Report Form (Part 1): Testing in Accordance
with NACE Standard TM0177 Method C—NACE Standard C-Ring Test ................... 27
Table 3—NACE Uniform Material Testing Report Form (Part 2): Testing in Accordance
with NACE Standard TM0177 Method C—NACE Standard C-RingTest .................... 28
Table 4—Arm Displacements for API and Other Grade Oilfield Tubular Steels............... 31
Table 5—Suggested Arm Displacements for Selected Alloys and Strength Levels ......... 32
Table 6—NACE Uniform Material Testing Report Form (Part 1): Testing in Accordance
with NACE Standard TM0177 Method D—NACE Standard DCB Test....................... 35
Table 6—NACE Uniform Material Testing Report Form (Part 2): Testing in Accordance
with NACE Standard TM0177 Method D—NACE Standard DCB Test....................... 36
________________________________________________________________________
CE International
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1.1 This standard covers the testing of metals subjected to
of test specimen. General guidelines to help to determine
the aptness of each test method are given at the beginning
1.3.1 For testing at ambient conditions, the test
Method B The statistically based critical stress factor (Sc)
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NACE International 1
(2)
American Petroleum Institute (API), 1220 L St. NW, Washington, DC 20005.
(3)
International Organization for Standardization (ISO), 1 rue de Varembé, Case postale 56, CH-1211 Geneva 20, Switzerland.
of each test method description (Sections 8 through 11).
Reporting of the test results is also discussed.
1.3 Metals can be tested for resistance to EC at
temperatures and pressures that are either ambient
(atmospheric) or elevated.
____________________________________
Section 2: EC T
2.1 Interpretation of stress corrosion test results is a
difficult task. The test methods contained in this standard
are severe, with accelerated tests making the evaluation of
the data extremely difficult. In testing the reproducibility of
the test methods among different laboratories, several
undesirable side effects (frequent with many accelerated
tests) that must be noted include:
2.1.1 The test environment may cause failure by HIC
and hydrogen blistering. This is especially true for
lower-strength steels not usually subject to SSC. HIC
may be detected by visual and metallographic
observations. Blistering is normally visible on the test
specimen surface. (For further information regarding
this phenomenon, see NACE Standard TM0284.5)
t NACE International
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for a 50% probability of failure in 720 hours.
Method C The highest no-failure stress in 720 hours.
Method D The average KISSC (threshold stress intensity
factor for SSC) for valid tests of replicate test
specimens.
1.5 Safety Precautions: H2S is an extremely toxic gas that
must be handled with care. (See Appendix A.)
___________________________________
sting Variability
2.1.2 The test environment may corrode some alloys
that normally do not corrode in actual field service and
thereby induce EC failures in alloys that ordinarily do
not fail by EC. This problem is especially acute with
the martensitic and precipitation-hardened stainless
steels.
2.2 Furthermore, other aspects to be considered in the
selection of test method(s) include:
2.2.1 Material anisotropy affecting mechanical
properties and EC susceptibility can be an important
parameter. The fracture path in the test specimen
should match what is anticipated in the actual
component.
Sections 1 through 7 of this standard give general
comments that apply to all four test methods. Sections 8
through 11 indicate the test method to follow for each type
informational purposes. This rating may be based on:
Method A The highest no-failure stress in 720 hours.
tensile stresses for resistance to cracking failure in low-pH
aqueous environments containing H2S. Carbon and low-
alloy steels are commonly tested for EC resistance at room
temperature where SSC susceptibility is typically high. For
other types of alloys the correlation of EC susceptibility with
temperature is more complicated.
1.2 This standard describes the reagents, test specimens,
and equipment to use, discusses base material and test
specimen properties, and specifies the test procedures to
follow. This standard describes four test methods:
Method A—Standard Tensile Test
Method B—Standard Bent-Beam Test
Method C—Standard C-Ring Test
Method D—Standard Double-Cantilever-Beam (DCB) Test
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procedures can be summarized as follows: Stressed
test specimens are immersed in acidified aqueous
environments containing H2S. Applied loads at
convenient increments can be used to obtain EC data.
1.3.2 For testing at temperatures higher than 27°C
(80°F), at either atmospher ic or elevated pressure,
Section 7 describes an alternative test technique. All
methods (A, B, C, and D) are adaptable to this
technique.
1.4 This standard may be used for release or acceptance
testing to ensure that the product meets a certain minimum
level of EC resistance as prescribed in API(2) Specification
5CT,3 ISO(3) 11960,4 or as prescribed by the user or
purchaser. This standard may also provide a quantitative
measure of the product’s EC resistance for research or
TM0177-2005
________________________________________________________________________
Section 1: General
nsee=