ISO 4680:2022
(Main)Corrosion of metals and alloys — Uniaxial constant-load test method for evaluating susceptibility of metals and alloys to stress corrosion cracking in high-purity water at high temperatures
Corrosion of metals and alloys — Uniaxial constant-load test method for evaluating susceptibility of metals and alloys to stress corrosion cracking in high-purity water at high temperatures
The document specifies a method for undertaking uniaxial constant load testing of the susceptibility of a metal, or an alloy, to stress corrosion cracking (SCC) in high-purity water environments at high temperature (above the boiling point of water at normal pressures) and pressure. The test method is particularly applicable to simulated primary water environments of light water reactors (LWRs). The test method enables assessment of the relative resistance to SCC of a material in different environments and the comparative resistance of different materials (using the same environment, specimen dimensions and loading). The terms “metal” and “alloy”, as used in the document, include weld metals and weld heat affected zones.
Corrosion des métaux et alliages — Méthode d'essai sous charge uniaxiale pour l'évaluation de la sensibilité des métaux et des alliages à la fissuration par corrosion sous contrainte dans l'eau de haute pureté à hautes températures
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 4680
First edition
2022-12
Corrosion of metals and alloys —
Uniaxial constant-load test method
for evaluating susceptibility of
metals and alloys to stress corrosion
cracking in high-purity water at high
temperatures
Corrosion des métaux et alliages — Méthode d'essai sous charge
uniaxiale pour l'évaluation de la sensibilité des métaux et des alliages
à la fissuration par corrosion sous contrainte dans l'eau de haute
pureté à hautes températures
Reference number
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative reference .1
3 Terms and definitions . 1
4 Principle . 2
5 Specimens. 2
5.1 General . 2
5.1.1 General requirements . 2
5.1.2 Categories and shapes of specimens. 2
5.1.3 Shapes and dimensions of grips/clevises . 2
5.1.4 Dimensions of specimen shoulder and radius . 2
5.1.5 Machined notch . 3
5.1.6 Dimensions of gauge section. 3
5.1.7 Serial loading of multiple specimens. 3
5.2 Preparation of specimens . 4
5.2.1 Orientation of specimen sampling . 4
5.2.2 Methods of specimen sampling . 4
5.2.3 Surface finishing . 5
5.2.4 Mechanical grinding and polishing. 5
5.2.5 Electrolytic or chemical polishing . 5
5.2.6 Marking . . 5
6 Test apparatus .7
6.1 Test set-up . 7
6.2 Loading mechanism . 7
6.3 Autoclave . 8
6.4 Circulating loop . . . 8
7 Experimental procedure .9
7.1 Test environment . 9
7.1.1 General . 9
7.1.2 Corrosion potential . 10
7.1.3 Measurement parameters . 10
7.2 Specimen number and applied stress . 10
7.3 Testing procedures . 10
7.3.1 General . 10
7.3.2 Test solution adjustment . 11
7.3.3 Temperature control . 11
7.3.4 Loading . 11
7.3.5 Unloading . 11
7.3.6 Completion of test. 11
7.4 Addition of crevice . 11
7.4.1 General . 11
7.4.2 Materials of crevice formation . 11
7.4.3 Procedure of crevice addition .12
7.5 Electrical resistance measurement methods . .12
7.5.1 General .12
7.5.2 Measurement requirements. 13
8 Assessment of results .13
8.1 Time to failure. 13
8.2 Validity of failure position . 13
8.3 Other evaluation indexes . .13
8.4 Observation of crack morphology . 13
8.5 Detection of crack initiation using electrical resistance measurement methods . 14
iii
9 Test report .14
Annex A (informative) A comparison of specimen orientations in standards .15
Annex B (normative) Measuring items of test solution .17
Annex C (informative) Water chemistry conditions and measurement items for simulated
BWR and PWR primary water environment tests .18
Annex D (informative) Procedures to interrupt and resume testing .20
Annex E (informative) Electrical resistance measurement methods .22
Annex F (informative) Test report items .25
Bibliography .27
iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html
v
INTERNATIONAL STANDARD ISO 4680:2022(E)
Corrosion of metals and alloys — Uniaxial constant-load
test method for evaluating susceptibility of metals and
alloys to stress corrosion cracking in high-purity water at
high temperatures
WARNING — This document can involve hazardous materials, operations and equipment. It is
the responsibility of the user of this document to consult and establish appropriate safety and
health practices and to determine the applicability of regulatory limitations prior to use.
1 Scope
The document specifies a method for undertaking uniaxial constant load testing of the susceptibility
of a metal, or an alloy, to stress corrosion cracking (SCC) in high-purity water environments at high
temperature (above the boiling point of water at normal pressures) and pressure. The test method is
particularly applicable to simulated primary water environments of light water reactors (LWRs).
The test method enables assessment of the relative resistance to SCC of a material in different
environments and the comparative resistance of different materials (using the same environment,
specimen dimensions and loading).
The terms “metal” and “alloy”, as used in the document, include weld metals and weld heat affected
zones.
2 Normative reference
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 7539-1, Corrosion of metals and alloys — Stress corrosion testing — Part 1: General guidance on testing
procedures
ISO 7539-4, Corrosion of metals and alloys — Stress corrosion testing — Part 4: Preparation and use of
uniaxially loaded tension specimens
ISO 8044, Corrosion of metals and alloys — Vocabulary
ISO 3785, Metallic materials — Designation of test specimen axes in relation to product texture
ISO 6892-1, Metallic materials — Tensile testing — Part 1: Method of test at room temperature
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7539-1, ISO 8044, ISO 3785
and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
test time
period between the start and the end of a test, with the criterion for the end being the initiation or
failure of all test pieces, or the passage of an agreed test duration.
Note 1 to entry: The start of a test is when a specimen(s) is first exposed to the specified water chemistry,
temperature and load.
4 Principle
The test consists of subjecting a specimen to uniaxial constant load in a specified and well-controlled
environment for a set time period. The susceptibility to SCC is evaluated based on the time to initiation
(for tests with in-situ monitoring), the time to failure, the extent of cracking (especially if no failure
occurs) and/or the test time (when no cracking is observed). Because the test times can rarely be
as long as the desired component lifetime, the test is carried out under accelerated test conditions
of temperature, or test solution. The accelerating factor introduced shall not induce a change in
crack initiation mechanism; the crack morphology shall be the same as expected or observed in the
engineering application. The accelerating factor adopted should be appropriate for the intended
application to evaluate the SCC susceptibility, but the accelerated nature of the laboratory initiation test
can produce a different quantitative effect of materials, environments or stresses. For example, for a
simulated boiling water reactor (BWR) water environment, the test may be accelerated by the addition
of sodium sulfate (Na SO ) or by the use of a crevice. On the other hand, for a simulated pressurized
2 4
water reactor (PWR) primary water environment, the test may be accelerated by an increase in test
temperature.
5 Specimens
5.1 General
5.1.1 General requirements
Shapes and dimensions of specimens shall be designed so as to ensure that SCC initiates in a gauge
section or at a machined notch. Since SCC susceptibility is affected by microstructure and surface
finishing, specimen orientation shall be categorized and deformation shall be minimised during
specimen preparation.
5.1.2 Categories and shapes of specimens
The specimen type and geometry shall be based on existing test standards such as ISO 7539-4 or
ISO 6892-1. Specimen types such as rod-shaped or plate-shaped tensile test specimens are recommended.
Tubular or annular specimens may be tested, if appropriate.
5.1.3 Shapes and dimensions of grips/clevises
Grips/clevises shall match the linkage of the testing machine, which is often a threaded connection. For
tensile specimens, load is often applied using pin or threaded connections.
When using pin loading, failure can occur at the pin hole, particularly in high strength materials, and
the specimen shall be designed with this in mind. In general, the ligament surrounding the pin hole
should be about twice the area of the gauge section, and the pin hole diameter should be at least as large
as the thickest dimension of the gauge section.
5.1.4 Dimensions of specimen shoulder and radius
Failure can also occur by stress concentration in the radius transition from the gauge section to the
grip section of tensile specimens, and a transition radius that is substantially larger than the gauge
section is recommended. Undercut at the final transition to the gauge section shall also be avoided. The
shapes in ISO 6892-1 provide excellent examples, but the underlying criterion is that failure should not
occur in the radius nor predominantly in the adjacent gauge section. The following recommendations
provide guidance for tensile loaded specimens.
a) For rod-shaped specimens, the radius of the shoulders (r) should be at least twice the diameter (d)
of the parallel section.
b) For plate-shaped specimens, the radius of the shoulders (r) should be equal to or greater than the
width of the parallel section (w).
5.1.5 Machined notch
Specimens with notches created mechanically in the parallel section may be used. The stress
concentration and multiaxial stress create a higher stress than the nominal stress calculated using the
minimum cross-sectional area of the bottom of the notch.
If the bottom of the notch is in the elastic region, the stress at the bottom of the notch should be
evaluated by multiplying the nominal stress by the stress concentration factor K for the shape of the
t
notch.
If the bottom of the notch is the plastic region, the stress distribution at the bottom of the notch changes
due to plastic deformation, so it is desirable to evaluate the stress using elasto-plastic analysis such as
finite element analysis.
5.1.6 Dimensions of gauge section
Dimension tolerances for preparing the gauge section of the specimen shall conform to ISO 6892-1. The
diameter, thickness and width of the machined gauge section are usually constant, and shall be uniform
over the entire length of the gauge section, specified in ISO 6892-1.
However, the gauge section of the specimen may be tapered towards the centre within tolerances
specified in ISO 6892-1. By tapering the gauge section of the specimen, it is possible to increase the
number of cracks at effective positions in the specimen’s gauge section and to reduce breakages at the
shoulder sections of the specimen.
Specimens having tapered gauge lengths may be employed for the purpose of obtaining a range of
initial stresses.
When a specimen shape other than those specified in ISO 6892-1 is necessary, the specimen shape
should ideally have a gauge length of 10 mm or more and a width of 3 mm or more in the parallel section.
With agreement among the parties involved in the testing, specimens that are smaller than those
described above may be used. Without careful consideration, it is possible that the results of the SCC
test can be greatly influenced by the cross-sectional area of the specimen and the area exposed to the
environment.
Caution has to be exercised in the case of miniature specimens, as machining becomes difficult when
the cross-sectional area of the specimen decreases, and elevated susceptibility to stress concentration
can result from pitting, general corrosion, bending, etc. The net section stress also rises rapidly as
cracks form. When using miniature specimens, it is recommended that the diameter and thickness of
the gauge section of the specimen be at least 6 times the grain size.
In general, larger specimens are preferred in terms of the reproducibility and relevance of the test
results.
5.1.7 Serial loading of multiple specimens
The constant load test may be performed by connecting multiple specimens in series. In this case, a
load-catch jig designed to prevent unloading after fracture of one specimen shall be used, or the time
of unloading be detected. Load-catch mechanisms need to consider whether shock re-loading to the
remaining specimens can occur after the failure of one specimen.
5.2 Preparation of specimens
5.2.1 Orientation of specimen sampling
The orientation of the specimen should account for the orientation of cracks of concern in the application
of interest. Often, specimens are machined so that the longitudinal direction of specimens matches
the rolling direction. The sampling direction and location of the specimens should be determined by
agreement among the parties involved in the testing.
The test specimen axes in relation to product texture should be designated by an X-Y-Z orthogonal
coordinate system specified in ISO 3785. The letter X denotes the direction of principal deformation
(maximum grain flow in the product). The letter Y denotes the direction of least deformation. The
letter Z denotes the direction normal to the X-Y plane. The anticipated direction of crack extension for
notched specimens should be designated using a hyphenated code wherein the letter(s) preceding the
hyphen represent the longitudinal direction of the specimens and the letter(s) following the hyphen
represent the anticipated direction of crack extension. For unnotched specimens, surfaces normal
to the anticipated direction of crack development are specified in plate-shaped specimens and are
not specified in rod-shaped specimens. The specified surface in plate-shaped specimens should
be designated using a hyphenated code wherein the letter(s) preceding the hyphen represent the
longitudinal direction of the specimens and the letter(s) following the hyphen represent the direction
normal to the surface.
The orientation of specimens sampled from test products is designed according to ISO 3785. The
orientations of unnotched plate-shaped specimens for sheet, plate, rectangular bar, cylinder and tube,
are shown in Figure 1. When the specimen direction is aligned with the product's characteristic grain-
flow directions, a single letter for each case is used to denote the direction perpendicular to the crack
plane and the direction of intended crack extension, as shown in Figures 1 a), b) and c). When the
specimen orientation directions lie midway between the product's characteristic grain-flow directions,
two letters shall be used to denote the normal to the crack plane or the crack propagation direction, as
shown in Figure 1 d).
Designations by an L-T-S orthogonal coordinate system for rectangular sections and by an L-R-C
[1]
orthogonal coordinate system for cylindrical sections specified in ASTM E399-20a are described
together in Figure 1. The designations of specimen sampling orientations are compared to ISO 3785,
[1] [2]
ASTM E399-20a and ASTM A370-20 in Annex A.
[1] [2]
NOTE For rectangular sections, the definition of orientations in ASTM E399-20a and ASTM A370-20
corresponds to that in ISO. For cylindrical sections, the definition of orientations in ASTM does not always
correspond to that in ISO because that in the ASTM standards is a geometry-based system.
When there is no grain-flow direction as in a casting, specimen location and crack plane orientation
shall be defined on a part drawing and the test result shall carry no orientation designation.
For plate-shaped specimens, the most relevant orientation is generally when the test specimen is
parallel to the rolling surface of the plate.
In the case of a use of cold or warm rolling to accelerate tests for material comparisons, the orientation
of the specimen for the rolling direction also should account for the orientation of cracks.
5.2.2 Methods of specimen sampling
Specimens can be extracted by sawing, electrical discharge machining, cutting, or grinding, provided
that damage to the material is minimised and constrained to the surface.
5.2.3 Surface finishing
Significant effects of surface conditions on the SCC initiation time are well known, and thus surface finish
needs to be carefully considered and well controlled. Concerns include physical defects, near-surface
microstructural changes (including plastic deformation and possible formation of nanocrystalline
layer), residual stress, increased hardness, and chemical contamination.
The increase of stress due to surface asperity usually has more of an effect on the SCC of high strength
materials than low strength materials.
Unless it is necessary to evaluate the as-supplied or as-fabricated surface, the material should be tested
with a reproducible surface finish by mechanical grinding or polishing, electropolishing or chemical
polishing.
Prior to testing the specimen shall be degreased using a solvent such as acetone and washing using
ethanol and high-purity water.
5.2.4 Mechanical grinding and polishing
Unless a manufacturing surface is being evaluated, the surface of a specimen should be carefully
prepared and controlled. A common surface preparation is the sequential use of coarser-to-finer
abrasives, and using cooling fluid is preferred, as described in ISO 3366 and ISO 21948. The final finish,
grinding or polishing should be agreed between the parties but as a default, a final finish of P600 is
recommended. The final grinding or polishing should be undertaken preferably in the longitudinal
direction of the specimen. However, other grinding and polishing conditions may be adopted by
agreement between the parties involved in testing.
In final machining and surface preparation, aggressive material removal and overheating should be
avoided to minimise residual stress and changes of microstructure on the surface.
Care should also be taken to minimise surface contamination from polishing residue.
5.2.5 Electrolytic or chemical polishing
Electrolytic or chemical polishing may be appropriate as they can reduce the machined layer or surface
roughness that result from the mechanical finishing of the surface. It should not be assumed that
electropolishing or chemical polishing always removes surface damage and defects, or that pitting or
localized corrosion does not occur during the process.
If the final surface finish is done using chemical treatment (polishing, etching, etc.), attention should be
taken when selecting conditions to avoid selective dissolution and the formation of undesirable residue
on the surface.
Chemical or electrochemical processes that generate hydrogen should not be used on materials that are
sensitive to hydrogen induced damage.
5.2.6 Marking
If it is necessary to mark specimens for identification, marks shall be put as far away as possible from
the areas where SCC initiation occurs and at positions that do not affect the test results.
Ends of an original gauge section may be marked with a fine mark or scribed line. Note that marking by
a punch shall be avoided because it can lead to premature fracture.
a) Sheet, plate, rectangular bar
b) Cylinder — Radial grain flow c) Cylinder — Axial grain flow
d) Tube (axial grain flow)
e) Not aligned
Key
1 X-Z (L-S) orientation specimen 13 X-Z (L-R) orientation specimen
2 Y-Z (T-S) orientation specimen 14 Y-Z (C-R) orientation specimen
3 X-Y (L-T) orientation specimen 15 X-Y (L-C) orientation specimen
4 Y-X (T-L) orientation specimen 16 Y-X (C-L) orientation specimen
5 Z-X (S-L) orientation specimen 17 Z-X (R-L) orientation specimen
6 Z-Y (S-T) orientation specimen 18 Z-Y (R-C) orientation specimen
7 X-Z (R-L) orientation specimen 19 XY-Z (LT-S) orientation specimen
8 Y-Z (C-L) orientation specimen 20 YZ-X (TS-L) orientation specimen
9 X-Y (R-C) orientation specimen 21 X-YZ (L-TS) orientation specimen
10 Y-X (C-R) orientation specimen X direction of principal deformation (maximum grain
flow in the product)
11 Z-X (L-R) orientation specimen Y direction of least deformation
12 Z-Y (L-C) orientation specimen Z direction normal to the X-Y plane
a
Grain flow.
Figure 1 — Convention for recoding orientation of unnotched plate-shaped specimens
6 Test apparatus
6.1 Test set-up
A typical test configuration is shown in Figure 2. It consists of a device that applies load to a specimen, a
test chamber for the specimen and the environment, and a circulation system including a water quality
control and monitoring. The test chamber is an autoclave designed for the high-temperature and high-
pressure environments that simulate the light water reactor water environments. The water control
and monitoring system is typically at normal temperature and pressure. The wetted system materials
are typically austenitic stainless steel or materials having higher corrosion resistance.
6.2 Loading mechanism
The loading device can be a mechanical loading system, a spring, a lever (cantilever), internal pressure
loading, or an air cylinder. A device that can load uniaxial tensile load with at least a ±1 % accuracy
[6]
is used. The force applied shall have passed the tolerance specified in ISO 7500-1 or ASTM E4. SCC
initiation can be sensitive to small decreases in load during testing, and thus highly controlled, active
loading is preferred.
6.3 Autoclave
The autoclave shall be a container capable of sealing and holding the target high-purity water at high
temperatures. The material of the autoclave shall be austenitic stainless steel or other corrosion
resistant material. A heater and temperature controller shall be used to control the temperature inside
the autoclave. The difference in temperature in the autoclave where specimens are located should be
within ±3 °C of the target value. For safe use of the autoclave, refer to the performance requirements
specified in ISO 16528-1 and ISO 16528-2.
6.4 Circulating loop
The water circulation loop is equipped with a high-pressure pump that feeds the controlled test solution
to the autoclave, and has a pressure regulating valve that can maintain the desired pressure. To measure
the water quality (see Annex B), install measuring devices on the inlet and outlet sides of the autoclave
as shown in Figure 2. The inlet side is measured at the normal temperature and low-pressure section
from the water-chemistry-controlling reservoir to the high-pressure pump. The autoclave outlet side is
the normal temperature and low-pressure part.
Key
1 water-chemistry-controlling reservoir 13 pressure-regulation valve
2 regulating gas injection system 14 flow meter
3 inlet water sampling point 15 outlet water sampling point
4 feed water pump 16 ion exchange resin
5 high-pressure pump 17 bypass line
6 accumulator 18 pressure meter
7 heat exchanger 19 thermocouple
8 preheater 20 solution conductivity meter
9 test chamber (autoclave with loading mechanism) 21 dissolved oxygen analyser
10 crack-initiation-detecting device 22 dissolved hydrogen analyser
11 corrosion-potential-measuring device 23 pH meter
12 cooler
Continuous line water line
Bold line high-pressure section of water line
Dashed line electrical instrumentation
Dotted line gas line
a
Unessential in the simulated PWR primary water system.
b
Unessential in the simulated BWR water system.
Figure 2 — Schematic of UCL test equipment configuration for evaluating SCC in simulated light
water reactor water environment
7 Experimental procedure
7.1 Test environment
7.1.1 General
By adjusting the water chemistry of the water-chemistry-controlling reservoir and circulating the test
water through the autoclave containing the specimen, the water chemistries at the inlet and outlet of
the autoclave are set as the target test conditions and should be as identical as possible and appropriate
to the purposes of the test. The simulated BWR water environments often represent normal water
chemistry (NWC) or hydrogen water chemistry (HWC). Examples of the water chemistry of the
simulated BWR water environment and PWR primary water environment test under the accelerated
condition are shown in Annex C. For tests in the simulated BWR water environments (see Table C.1), the
autoclave outlet water should flow through the ion-exchange resin to eliminate impurity ions. Then, the
test water is returned to the water-chemistry-controlling reservoir. In simulated PWR primary water
environments, if the test water contains borate ions and lithium ions (see Table C.2), the autoclave
outlet can directly return to the reservoir, or (preferably) flow through an ion-exchange resin that is
equilibrated to the desired water-chemistry.
7.1.2 Corrosion potential
Measurement of the corrosion potential of the specimen or a separate electrode versus a reference
electrode should employ a high-input-impedance electrometer. The electrodes shall be electrically
isolated. The measurement of the corrosion potential should be performed throughout the test.
7.1.3 Measurement parameters
The parameters shown in Annex B should be measured during the test. There are differences in some
parameters for the simulated BWR water environment test and the simulated PWR primary water
environment test due to the difference in the water chemistries.
7.2 Specimen number and applied stress
The number of test specimens per condition shall be multiple as determined by agreement between
the parties according to the test purpose. When comparing the SCC susceptibility of different materials
using the time to failure, it is desirable from a statistical perspective that the number of test specimens
should be seven or more.
The initial stress applied to the specimen should be determined by dividing the applied load by the
initial cross-sectional area of the gauge section in the specimen. If the dimensions of the gauge section
are within the tolerances defined in ISO 6892-1, the nominal dimension may be used for calculating the
original cross-sectional area. If they are not within the tolerances, the dimensions of all specimens shall
be measured.
For a specimen having a tapered gauge length, the range of initial stresses applied to the specimen
should be agreed between the parties. The minimum and maximum initial stresses are determined
by dividing the applied load by the maximum and minimum initial cross-sectional areas of the gauge
section in the specimen, respectively. The dimensions of all specimens shall be measured.
7.3 Testing procedures
7.3.1 General
The testing procedure is as followed. The specimen is installed and set in the autoclave, and water
chemistry is adjusted in the autoclave with the circulation system and the desire pressure achieved.
The temperature in the autoclave shall then be increased and controlled at the test temperature
before applying load. If a specimen with a crevice is used, the crevice is created before installation.
The test is terminated when the number of specimens that have failed reaches an agreed threshold.
In the case of monitoring using an electrical resistance measurement (see 7.5), the test is terminated
when the number of specimens for which the time to initiation has been detected by the monitoring
reaches an agreed threshold. Alternatively, the test may be terminated once the duration passes an
agreed threshold. The threshold for the number of specimens and the test duration should be pre-
determined by the interested parties. After the test duration passes, the heater is shut down to decrease
temperature. If the specimen has not failed, it should be unloaded before the heater is shut down to
avoid an overload of the specimen from thermal shrinkage difference with pull rods should the systems
trip. When the temperature decreases to room temperature, the pressure in the system is decreased to
normal pressure, and the specimen is removed. The procedure of loading and unloading is determined
on the basis of discussion between interested parties for the test objectives. Ideally, the test is not
interrupted until all specimens fail. The test may be interrupted on the basis of discussion between
interested parties and the consideration of the effect on the test results. Recommended procedures for
the interruption and restart are detailed in Annex D.
7.3.2 Test solution adjustment
After installation of the specimens, water chemistry including dissolved oxygen concentration and
dissolved hydrogen concentration shall be adjusted to the specified chemistry in the circulation system.
7.3.3 Temperature control
After the desired pressure in the system is achieved, the water in the autoclave is heated. The
temperature ramp rate is recommended to be at least 50 °C/hour to limit corrosion during heat up.
Overshooting is undesirable, so often it is wise to heat to a temperature 10 °C to 20 °C below the test
temperature, then increase it. To prevent boiling or the creation of a steam bubble near the top of the
autoclave, the system pressure should provide a margin of at least 10 °C. Unintended stressing of the
specimens by the difference in the thermal expansion coefficient to the loading equipment or test jigs
should be considered.
7.3.4 Loading
If the specimen is loaded by an external loading system, this is done after stable water temperature and
chemistry is achieved in the autoclave. External loading systems can be a servo system, spring system,
lever system, internal pressure system, or air cylinder system. Note that some internal pressure
systems loaded by the difference in pressure inside and outside the autoclave should consider making
the final increase in system pressure after stable conditions are achieved. Seal resistance for pull-rods
should also be accounted for.
7.3.5 Unloading
At the end of the pre-determined test duration, the specimen should be unloaded, and subsequently the
temperature decreased.
7.3.6 Completion of test
When the pre-determined number of specimens have failed, when the time to initiation has been
detected on the pre-determined number of specimens, or when the pre-determined test duration is
achieved, the test temperature is decreased to room temperature and the pressure is decreased to
ambient pressure. After that, the circulation system is stopped, the autoclave is drained and opened,
and the specimens are removed. Specimens should be cleaned using high-purity water or ethanol and
then dried. Characterisation of the specimen can now be performed to confirm if SCC has occurred.
7.4 Addition of crevice
7.4.1 General
The crevice design is based on agreement between the interested parties. A crevice facilitates the
formation of a favourable environment for SCC to initiate, and has the largest effect in oxidizing
environments.
7.4.2 Materials of crevice formation
Crevice forming materials shall be stable in the test environment and shall create a geometry that
strongly limits mass transfer in a repeatable manner. As a crevice forming material, unwoven fabric or
metal foil is recommended for use. For example, high-purity-graphite-fibre unwoven fabric or stainless
steel foil is used. The metallic crevice forming material should be of the same metal as the specimen.
Impurities associated with the crevice-forming material can impact the crack initiation process.
Appropriate procedures, such as prior rinsing or immersion in high-purity water, should be undertaken
to remove these impurities.
7.4.3 Procedure of crevice addition
The specimen and the crevice forming material, including any fixtures, shall be degreased using
acetone, ethanol, and high-purity water. The crevice forming material is attached on the specimen with
the fixtures by bolts and nuts, as shown in Figure 3.
If metal foil is used as the crevice forming material, the metal foil should be tightly wrapped ar
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...