ASTM F2078-22

Standard Terminology Relating to Hydrogen Embrittlement Testing

SIGNIFICANCE AND USE
3.1 The terms used in describing hydrogen embrittlement have precise definitions. The terminology and its proper usage must be completely understood to communicate and transfer information adequately within the field.  
3.2 The terms defined in other terminology standards are respectively identified in parentheses following the definition.
SCOPE
1.1 This terminology covers the principal terms, abbreviations, and symbols relating to mechanical methods for hydrogen embrittlement testing. These definitions are published to encourage uniformity of terminology in product specifications.  
1.2 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: 30-Apr-2022
• ICS: 01.040.19 - Testing (Vocabularies)
• ICS: 19.040 - Environmental testing
• Technical Committee: F07 - Aerospace and Aircraft
• Drafting Committee: F07.04 - Hydrogen Embrittlement

Relations

• Refers: ASTM E1823-24a - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Feb-2024
• Refers: ASTM E1823-24 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2024
• Refers: ASTM E8/E8M-24 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jan-2024
• Refers: ASTM E1823-20 - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Feb-2020
• Refers: ASTM C904-01(2018) - Standard Terminology Relating to Chemical-Resistant Nonmetallic Materials
• Effective Date: 01-Nov-2018
• Refers: ASTM F1624-12(2018) - Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique
• Effective Date: 01-Nov-2018
• Refers: ASTM D4848-98(2018) - Standard Terminology Related to Force, Deformation and Related Properties of Textiles
• Effective Date: 01-Sep-2018
• Refers: ASTM E8/E8M-16 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 15-Jul-2016
• Refers: ASTM E631-15 - Standard Terminology of Building Constructions
• Effective Date: 01-Mar-2015
• Refers: ASTM E8/E8M-15 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Feb-2015
• Refers: ASTM E631-14 - Standard Terminology of Building Constructions
• Effective Date: 01-Nov-2014
• Refers: ASTM E8/E8M-13 - Standard Test Methods for Tension Testing of Metallic Materials
• Effective Date: 01-Jun-2013
• Refers: ASTM E1823-12e - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Dec-2012
• Refers: ASTM E1823-12d - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 15-Nov-2012
• Refers: ASTM E1823-12c - Standard Terminology Relating to Fatigue and Fracture Testing
• Effective Date: 01-Sep-2012

Overview

ASTM F2078-22: Standard Terminology Relating to Hydrogen Embrittlement Testing provides authoritative definitions for key terms, abbreviations, and symbols used in mechanical testing for hydrogen embrittlement. Developed by ASTM Committee F07 on Aerospace and Aircraft, this standard ensures accurate and uniform terminology for users involved in hydrogen embrittlement testing, research, and product specification development.

Hydrogen embrittlement is a critical factor affecting metal performance, particularly in high-strength components used in aerospace, automotive, and industrial applications. This standard enhances technical communication and supports the effective transfer of information by clearly defining essential terms.

Key Topics

• Precise Terminology: Defines core concepts such as hydrogen embrittlement (HE), internal hydrogen embrittlement (IHE), environmental hydrogen embrittlement (EHE), embrittlement, ductility, brittleness, crack strength, stress, strain, and susceptibility ratios.
• Symbols and Abbreviations: Compiles and standardizes symbols and abbreviations frequently used in hydrogen embrittlement testing, aiding clarity and reducing misinterpretation.
• Modes and Mechanisms: Explains various mechanisms of hydrogen-induced damage, such as hydrogen-assisted stress cracking (HASC), stress corrosion cracking (SCC), fast fracture strength (FFS), and the impact of residual stresses.
• Testing Parameters: Covers common testing methods, critical measurement parameters (e.g., threshold stress intensity, applied load, notched tensile strength), and the significance of test environments (air vs. hydrogen-charged).
• Consistency Across Standards: Aligns definitions with related ASTM standards to foster consistency within the materials testing and engineering communities.

Applications

ASTM F2078-22 is essential for professionals engaged in:

• Hydrogen Embrittlement Testing: Laboratories and engineers performing mechanical testing of metals and alloys for hydrogen embrittlement susceptibility utilize this terminology to standardize test outputs and interpretations.
• Aerospace and Automotive Industries: Designers and manufacturers of high-strength fasteners and structural components rely on uniform terminology for specification, quality control, and failure analysis.
• Materials Research & Development: Researchers developing hydrogen-resistant materials and coatings reference this standard to ensure consistency in communication, data reporting, and publication.
• Product Specification Development: Standards developers and technical committees use these definitions in product specifications and related documentation to avoid ambiguity.
• Training and Education: Academic programs and industry training on hydrogen embrittlement phenomena benefit from the standardized terms when educating new engineers and material scientists.

By adopting ASTM F2078-22, organizations ensure precise, globally recognized language when discussing hydrogen embrittlement assessment, helping reduce errors and improving international collaboration.

Related Standards

ASTM F2078-22 is interconnected with several other important ASTM terminology and test method standards, including:

• ASTM F1624 – Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique
• ASTM E8/E8M – Test Methods for Tension Testing of Metallic Materials
• ASTM E1823 – Terminology Relating to Fatigue and Fracture Testing
• ASTM E6 – Terminology Relating to Methods of Mechanical Testing
• ASTM G15/G193 – Terminology and Acronyms Relating to Corrosion and Corrosion Testing
• ASTM D4848 – Terminology Related to Force, Deformation, and Related Properties of Textiles
• ASTM C904 – Terminology Relating to Chemical-Resistant Nonmetallic Materials

Consulting related ASTM standards ensures comprehensive understanding and robust application of terminology within hydrogen embrittlement testing and broader mechanical and corrosion assessment contexts.

Keywords: ASTM F2078-22, hydrogen embrittlement, terminology, mechanical testing, internal hydrogen embrittlement, environmental hydrogen embrittlement, standards, aerospace, stress corrosion cracking, testing methods.

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: F2078 − 22
Standard Terminology Relating to
Hydrogen Embrittlement Testing
This standard is issued under the fixed designation F2078; 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 must be completely understood to communicate and transfer
information adequately within the field.
1.1 This terminology covers the principal terms,
abbreviations, and symbols relating to mechanical methods for 3.2 The terms defined in other terminology standards are
hydrogen embrittlement testing. These definitions are pub- respectively identified in parentheses following the definition.
lished to encourage uniformity of terminology in product
4. Terminology
specifications.
4.1 Definitions:
1.2 This international standard was developed in accor-
baking—heating to a temperature, not to exceed 50 °F
dance with internationally recognized principles on standard-
(27.8 °C) below the tempering or aging temperature of the
ization established in the Decision on Principles for the
metaloralloy,inordertoremovehydrogenbeforeembrittle-
Development of International Standards, Guides and Recom-
ment occurs by the formation of microcracks.
mendations issued by the World Trade Organization Technical
DISCUSSION—No metallurgical changes take place as a result of
Barriers to Trade (TBT) Committee.
baking.
2. Referenced Documents
brittle—see brittleness.
2.1 ASTM Standards:
brittleness—the tendency of a material to break at a very low
C904 Terminology Relating to Chemical-Resistant Nonme-
strain, elongation, or deflection, and to exhibit a clean
tallic Materials
fracture surface with no indications of plastic deformation.
D4848 Terminology Related to Force, Deformation and
(E631)
Related Properties of Textiles
crack—line of fracture without complete separation. (F109)
E6 Terminology Relating to Methods of Mechanical Testing
E8/E8M Test Methods for Tension Testing of Metallic Ma-
crack strength—themaximumvalueofthenominalstressthat
terials
a cracked specimen is capable of sustaining. (E1823)
E631 Terminology of Building Constructions
ductile—see ductility.
E1823 TerminologyRelatingtoFatigueandFractureTesting
F109 Terminology Relating to Surface Imperfections on
ductility—the ability of a material to deform plastically before
Ceramics
fracturing. (E6)
F1624 Test Method for Measurement of Hydrogen Em-
embrittle—see embrittlement.
brittlement Threshold in Steel by the Incremental Step
Loading Technique
embrittlement—the severe loss of ductility or toughness, or
G193 Terminology and Acronyms Relating to Corrosion
both, of a material, usually a metal or alloy. (G193)
3. Significance and Use
environmental hydrogen embrittlement (EHE)—hydrogen
embrittlement caused by hydrogen introduced into a steel/
3.1 The terms used in describing hydrogen embrittlement
metallic alloy from an environmental source coupled with
have precise definitions. The terminology and its proper usage
stress either residual or externally applied.
DISCUSSION—Produces a clean intergranular fracture and is not
This terminology standard is under the jurisdiction of ASTM Committee F07
reversible. For the subtle differences between EHE and IHE, see Table
on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.04
X1.1.
on Hydrogen Embrittlement.
Current edition approved May 1, 2022. Published May 2022. Originally
environmentally assisted cracking (EAC)—see stress cor-
approved in 2001. Last previous edition approved in 2015 as F2078 – 15. DOI:
rosion cracking.
10.1520/F2078-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
fast fracture strength (FFS)—the load at which a sample
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
fractures when loaded at a rate consistent withTest Methods
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. E8/E8M
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2078 − 22
fracture strength—the normal stress at the beginning of stress—the resistance to deformation developed within a
fracture. material subjected to an external force. (D4848)
stress concentration factor (k )—the ratio of the greatest
gaseous hydrogen embrittlement (GHE)—a distinct form of
t
EHE caused by the presence of external sources of high stress in the region of a notch or other stress concentrator, as
determined by the theory of elasticity or by experimental
pressure hydrogen gas; cracking initiates on the outer
surface. procedures that give equivalent values, to the corresponding
nominal stress. (E1823)
heat treatment—heating and cooling processes that produce
stress corrosion cracking (SCC)—a cracking process that
metallurgical changes in the metallic alloy which alter the
requiresthesimultaneousactionofacorrodentandsustained
mechanical properties and microstructure of the metal.
tensile stress.
hydrogen-assisted stress cracking (HASC)—crackgrowthas
DISCUSSION—This excludes corrosion-reduced sections that fail by
aresultofthepresenceofhydrogen,whichcanbeeitherIHE
fast fracture. It also excludes intercrystalline or transcrystalline
or EHE and sometimes is referred to as hydrogen stress corrosion, which can disintegrate an alloy without either applied or
residual stress (G193). In essence, the process of SCC and EAC are
cracking (HSC).
equivalent.
hydrogen embrittlement (HE)—a permanent loss of ductility
stress–intensity factor, K—the magnitude of the mathemati-
in a metal or alloy caused by absorption of hydrogen in
cally ideal crack–tip stress field (stress field singularity) for
combination with stress, either an externally applied or an
a particular mode in a homogeneous linear–elastic body.
internal residual stress.
(E1823)
hydrogen embrittlement relief—see baking. DISCUSSION—K =for a Mode I (opening mode) loading condition that
I
displaces the crack faces in a direction normal to the crack plane.
hydrogen-induced stress cracking—see hydrogen-assisted
K =for a Mode II (sliding mode) loading condition where the crack
II
stress cracking.
facesaredisplacedinshearslidinginthecrackplaneandintheprimary
crack propagation direction.
hydrogen stress cracking—crack growth as a result of the
K =for a Mode III (tearing mode) loading condition where the crack
III
presence of hydrogen, which can be either IHE or EHE; also
faces are displaced in shear tearing in the crack plane but normal to the
see hydrogen-assisted stress cracking. primary crack propagation direction.
susceptibility to hydrogen embrittlement—a material prop-
hydrogen susceptibility ratio (Hsr)—the ratio of the thresh-
erty that is measured by the threshold stress intensity
old for the onset of hydrogen-assisted cracking to the tensile
parameter for hydrogen induced stress cracking, K ,K
strength of the material.
Iscc IHE
,orK , which is a function of hardness and microstruc-
EHE
internal hydrogen embrittlement (IHE)—hydrogen em-
ture.
brittlement caused by absorbed atomic hydrogen into the
threshold (th)—a point, separating conditions that will pro-
steel/metallic alloy from an industrial hydrogen emitting
duceagiveneffect,fromconditionsthatwillnotproducethe
process coupled with stress, either residual or externally
effect; the lowest load at which subcritical cracking can be
applied.
detected.
DISCUSSION—For the subtle differences between IHE and EHE, see
Table X1.1.
threshold stress (σ )—a stress below which no hydrogen
th
notched tensile strength (NTS)—the maximum nominal (net stress cracking will occur and above which time-delayed
section) stress that a notched tensile specimen is capable of fracture will occur.
sustaining. (E1823)
threshold stress intensity (K )—a stress intensity below
th
process—a defined event or sequence of events in plating or which no hydrogen stress cracking will occur and above
which, time-delayed fracture will occur.
coating that may include pretreatments and posttreatments.
time-delayed embrittlement—see internal hydrogen em-
reaction hydrogen embrittlement (RHE)—irreversible em-
brittlement.
brittlement caused by the reaction of hydrogen with metal to
form a stable hydride.
4.2 Symbols:
K—stress-intensity factor
residual stress—stress in a metal in the absence of external
K —Environmental Hydrogen Embrittlement (EHE)
EHE
forces.
threshold stress intensity at a specified loading rate—test
sharp-notch strength—the maximum nominal (net section)
conducted in a specified hydrogen charging environment —
stress that a sharply notched specimen is capable of sustain-
not geometry dependent.
ing. (E1823)
K —Internal Hydrogen Embrittlement (IHE) threshold
IHE
stress intensity
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F2078 − 15 F2078 − 22
Standard Terminology Relating to
Hydrogen Embrittlement Testing
This standard is issued under the fixed designation F2078; 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
1.1 This terminology covers the principal terms, abbreviations, and symbols relating to mechanical methods for hydrogen
embrittlement testing, which are present in more than one of the standards under the jurisdiction of ASTM Committee F07 on
Aerospace and Aircraft. testing. These definitions are published to encourage uniformity of terminology in product specifications.
1.2 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.
2. Referenced Documents
2.1 ASTM Standards:
C904 Terminology Relating to Chemical-Resistant Nonmetallic Materials
D4848 Terminology Related to Force, Deformation and Related Properties of Textiles
E6 Terminology Relating to Methods of Mechanical Testing
E8E8/E8M Test Methods for Tension Testing of Metallic Materials [Metric] E0008_E0008M
E631 Terminology of Building Constructions
E1823 Terminology Relating to Fatigue and Fracture Testing
F109 Terminology Relating to Surface Imperfections on Ceramics
F1624 Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique
G15G193 Terminology and Acronyms Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
3. Significance and Use
3.1 The terms used in describing hydrogen embrittlement have precise definitions. The terminology and its proper usage must be
completely understood to communicate and transfer information adequately within the field.
3.2 The terms defined in other terminology standards,standards are respectively identified in parentheses following the definition.
4. Terminology
4.1 Definitions:
This terminology standard is under the jurisdiction of ASTM Committee F07 on Aerospace and Aircraft and is the direct responsibility of Subcommittee F07.04 on
Hydrogen Embrittlement.
Current edition approved Nov. 1, 2015May 1, 2022. Published November 2015May 2022. Originally approved in 2001. Last previous edition approved in 20082015 as
F2078F2078 – 15.–08A. DOI: 10.1520/F2078-15.10.1520/F2078-22.
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 ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2078 − 22
baking—heating to a temperature, not to exceed 50°F (27.8°C)50 °F (27.8 °C) below the tempering or aging temperature of the
metal or alloy, in order to remove hydrogen before embrittlement occurs by the formation of microcracks.
DISCUSSION—
No metallurgical changes take place as a result of baking.
brittle—see brittleness.
brittleness—the tendency of a material to break at a very low strain, elongation, or deflection, and to exhibit a clean fracture
surface with no indications of plastic deformation. (E631)
crack—line of fracture without complete separation. (F109)
crack strength—the maximum value of the nominal stress that a cracked specimen is capable of sustaining. (E1823)
ductile—see ductility.
ductility—the ability of a material to deform plastically before fracturing. (E6)
embrittle—see embrittlement.
embrittlement—the severe loss of ductility or toughness, or both, of a material, usually a metal or alloy. (G15G193)
environmental hydrogen embrittlement (EHE)—hydrogen embrittlement caused by hydrogen introduced into a steel/metallic
alloy from an environmental source coupled with stress either residual or externally applied.
DISCUSSION—
Produces a clean intergranular fracture and is not reversible. For the subtle differences between EHE and IHE, see Table X1.1.
environmentally assisted cracking (EAC)—see stress corrosion cracking.
fast fracture strength (FFS)—the load at which a sample fractures when loaded at a rate consistent with Test Methods E8/E8M
fracture strength—the normal stress at the beginning of fracture.
gaseous hydrogen embrittlement (GHE)—a distinct form of EHE caused by the presence of external sources of high pressure
hydrogen gas; cracking initiates on the outer surface.
heat treatment—heating and cooling processes that produce metallurgical changes in the metallic alloy which alter the
mechanical properties and microstructure of the metal.
hydrogen-assisted stress cracking (HASC)—crack growth as a result of the presence of hydrogen, which can be either IHE
or EHE and sometimes is referred to as hydrogen stress cracking (HSC).
hydrogen embrittlement (HE)—a permanent loss of ductility in a metal or alloy caused by absorption of hydrogen in
combination with stress, either an externally applied or an internal residual stress.
hydrogen embrittlement relief—see baking.
hydrogen-induced stress cracking—see hydrogen-assisted stress cracking.
F2078 − 22
hydrogen stress cracking—crack growth as a result of the presence of hydrogen, which can be either IHE or EHE; also see
hydrogen-assisted stress cracking.
hydrogen susceptibility ratio (Hsr)—the ratio of the threshold for the onset of hydrogen-assisted cracking to the tensile
strength of the material.
internal hydrogen embrittlement (IHE)—hydrogen embrittlement caused by absorbed atomic hydrogen into the steel/metallic
alloy from an industrial hydrogen emitting process coupled with stress, either residual or externally applied.
DISCUSSION—
For the subtle differences between IHE and EHE, see Table X1.1.
notched tensile strength (NTS)—the maximum nominal (net section) stress that a notched tensile specimen is capable of
sustaining. (E1823)
process—a defined event or sequence of events in plating or coating that may include pretreatments and posttreatments.
reaction hydrogen embrittlement (RHE)—irreversible embrittlement caused by the reaction of hydrogen with metal to form
a stable hydride.
residual stress—stress in a metal in the absence of external forces.
sharp-notch strength—the maximum nominal (net section) stress that a sharply notched specimen is capable of sustaining.
(E1823)
strain—deformation of a material caused by the application of an external force. (D4848)
strain rate—the rate of relative length deformation with time due to an applied stress. (C904)
stress—the resistance to deformation developed within a material subjected to an external force. (D4848)
stress concentration factor (k )—the ratio of the greatest stress in the region of a notch or other stress concentrator, as
t
determined by the theory of elasticity or by experimental procedures that give equivalent values, to the corresponding nominal
stress. (E1823)
stress corrosion cracking (SCC)—a cracking process that requires the simultaneous action of a corrodent and sustained tensile
stress.
DISCUSSION—
This excludes corrosion-reduced sections that fail by fast fracture. It also excludes intercrystalline or transcrystalline corrosion, which can disintegrate
an alloy without either applied or residual stress (G15G193). In essence, the process of SCC and EAC are equivalent.
stress–intensity factor, K—the magnitude of the mathematically ideal crack–tip stress field (stress field singularity) for a
particular mode in a homogeneous linear–elastic body. (E1823)
DISCUSSION—
K =for a Mode I (opening mode) loading condition that displaces the crack faces in a direction normal to the crack plane.
I
K =for a Mode II (sliding mode) loading condition where the crack faces are displaced in shear sliding in the crack plane and in the primary crack
II
propagation direction.
K =for a Mode III (tearing mode) loading condition where the crack faces are displaced in shear tearing in the crack plane but normal to the primary
III
crack propagation direction.
susceptibility to hydrogen embrittlement— is a material property that is measured by the threshold stress intensity parameter
for hydrogen induced stress cracking, K , K , or K , which is a function of hardness and microstructure.
Iscc IHE EHE
F2078 − 22
threshold (th)—a point, separating conditions that will produce a given effect, from conditions that will not produce the effect;
the lowest load at which subcritical cracking can be detected.
threshold stress (σ )—a stress below which no hydrogen stress cracking will occur and above which time-delayed fracture will
th
occur.
threshold stress intensity (K )—a stress intensity below which no hydrogen stress cracking will occur and above which,
th
time-delayed fracture will occur.
time-delayed embrittlement—see internal hydrogen embrittlement.
4.2 Symbols:
P—applied load
P — critical load required to rupture a specimen using a continuous loading rate
c
P — crack initiation load for a given loading and environmental condition using an incrementally increasing load under
i
displacement control
P — threshold load in which P is invariant with respect to loading rate; P is the basis for calculating the threshold stress or
th i th
the threshold stress intensity
σ—applied stress
σ —net stress based on area at minimum diameter of notched round bar
net
σ —stress at crack i
...