ASTM E21-20
(Test Method)Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
Standard Test Methods for Elevated Temperature Tension Tests of Metallic Materials
SIGNIFICANCE AND USE
4.1 The elevated-temperature tension test gives a useful estimate of the ability of metals to withstand the application of applied tensile forces. Using established and conventional relationships it can be used to give some indication of probable behavior under other simple states of stress, such as compression, shear, etc. The ductility values give a comparative measure of the capacity of different materials to deform locally without cracking and thus to accommodate a local stress concentration or overstress; however, quantitative relationships between tensile ductility and the effect of stress concentrations at elevated temperature are not universally valid. A similar comparative relationship exists between tensile ductility and strain-controlled, low-cycle fatigue life under simple states of stress. The results of these tension tests can be considered as only a questionable comparative measure of the strength and ductility for service times of many hours. Therefore, the principal usefulness of the elevated-temperature tension test is to assure that the tested material is similar to reference material when other measures such as chemical composition and microstructure also show the two materials are similar.
SCOPE
1.1 These test methods cover procedure and equipment for the determination of tensile strength, yield strength, elongation, and reduction of area of metallic materials at elevated temperatures.
1.2 Determination of modulus of elasticity and proportional limit are not included.
1.3 Tension tests under conditions of rapid heating or rapid strain rates are not included.
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.6 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
Relations
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: E21 − 20
Standard Test Methods for
Elevated Temperature Tension Tests of Metallic Materials
This standard is issued under the fixed designation E21; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* E29 Practice for Using Significant Digits in Test Data to
Determine Conformance with Specifications
1.1 These test methods cover procedure and equipment for
E74 Practices for Calibration and Verification for Force-
thedeterminationoftensilestrength,yieldstrength,elongation,
Measuring Instruments
and reduction of area of metallic materials at elevated tempera-
E83 Practice for Verification and Classification of Exten-
tures.
someter Systems
1.2 Determination of modulus of elasticity and proportional
E177 Practice for Use of the Terms Precision and Bias in
limit are not included.
ASTM Test Methods
1.3 Tension tests under conditions of rapid heating or rapid E220 Test Method for Calibration of Thermocouples By
Comparison Techniques
strain rates are not included.
E633 Guide for Use of Thermocouples in Elevated-
1.4 The values stated in inch-pound units are to be regarded
Temperature Mechanical Testing
as standard. The values given in parentheses are mathematical
E691 Practice for Conducting an Interlaboratory Study to
conversions to SI units that are provided for information only
Determine the Precision of a Test Method
and are not considered standard.
1.5 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions of terms relating to tension testing which
responsibility of the user of this standard to establish appro-
appear in Terminology E6, apply to this test method. These
priate safety, health, and environmental practices and deter-
terms include alignment, axial strain, bending strain, gauge
mine the applicability of regulatory limitations prior to use.
length, elongation, elongation after fracture, extensometer
1.6 This international standard was developed in accor-
system, necking, reduction of area, tensile strength, yield
dance with internationally recognized principles on standard-
strength. In addition, the definitions of the following terms
ization established in the Decision on Principles for the
relating to tension testing are included.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical 3.1.1 Definitions of terms relating to tension testing which
appear in E6, shall apply to the terms used in this test method.
Barriers to Trade (TBT) Committee.
3.2 Definitions:
2. Referenced Documents
3.2.1 indicated temperature, n—the temperature indicated
2.1 ASTM Standards:
by the temperature-measuring system that meets the require-
E4 Practices for Force Verification of Testing Machines
ments of this standard.
E6 Terminology Relating to Methods of Mechanical Testing
3.2.2 specified temperature—the test temperature requested
E8/E8M Test Methods for Tension Testing of Metallic Ma-
by and reported to the customer.
terials
3.2.3 temperature-measuring system, n—a system consist-
ing of one or more temperature-measuring transducers with the
1 appropriate indicating instruments, extension wires, reference
These test methods are under the jurisdiction of ASTM Committee E28 on
Mechanical Testing and are the direct responsibility of Subcommittee E28.04 on
junctions or ice points, and data acquisition devices.
Uniaxial Testing.
3.2.3.1 Discussion—The temperature-measuring transducer
Current edition approved Sept. 1, 2020. Published October 2020. Originally
ɛ1
is usually a thermocouple.
approved in 1933. Last previous edition approved in 2017 as E21 – 17 . DOI:
10.1520/E0021-20.
3.2.3.2 Discussion—The use of the term measuring system
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
conformstothedefinitionof "measuringsystem”intheJCGM:
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
International Vocabulary of Metrology – Basic and General
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. Concepts and Associated terms (VIM).
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E21−20
4. Significance and Use rods, and grips used in elevated temperature testing. The
specimen form should be the same as that used during the
4.1 The elevated-temperature tension test gives a useful
elevated-temperature tests and designed so that only elastic
estimate of the ability of metals to withstand the application of
strains occur throughout the reduced section. This requirement
applied tensile forces. Using established and conventional
may necessitate use of a material different from that used
relationships it can be used to give some indication of probable
during the elevated-temperature test. See Practice E1012 for
behavior under other simple states of stress, such as
recommended methods for determining specimen alignment.
compression, shear, etc. The ductility values give a compara-
5.1.2.3 Gripping devices and pull rods may oxidize, warp,
tive measure of the capacity of different materials to deform
andcreepwithrepeateduseatelevatedtemperatures.Increased
locally without cracking and thus to accommodate a local
bending stresses may result. Therefore, grips and pull rods
stress concentration or overstress; however, quantitative rela-
should be periodically retested for axiality and reworked when
tionships between tensile ductility and the effect of stress
necessary.
concentrations at elevated temperature are not universally
5.1.3 Thetestingmachineshallbeequippedwithameansof
valid.Asimilar comparative relationship exists between tensile
measuring and controlling either the strain rate or the rate of
ductility and strain-controlled, low-cycle fatigue life under
crosshead motion or both to meet the requirements in 9.6.
simple states of stress. The results of these tension tests can be
5.1.4 For elevated-temperature testing of materials that are
considered as only a questionable comparative measure of the
readily attacked by their environment (such as oxidation of
strength and ductility for service times of many hours.
metalinair),thespecimenmaybeenclosedinacapsulesothat
Therefore, the principal usefulness of the elevated-temperature
it can be tested in a vacuum or inert gas atmosphere. When
tension test is to assure that the tested material is similar to
such equipment is used, the necessary corrections must be
reference material when other measures such as chemical
made to determine the actual forces seen by the specimen. For
composition and microstructure also show the two materials
instance, compensation must be made for differences in pres-
are similar.
sures inside and outside of the capsule and for any variation in
5. Apparatus
the forces applied to the specimen due to sealing ring friction,
bellows or other features.
5.1 Testing Machine:
5.1.1 The accuracy of the testing machine shall be within
5.2 Heating Apparatus:
the permissible variation specified in Practices E4.
5.2.1 The apparatus for and method of heating the speci-
5.1.2 Precaution should be taken to assure that the force on
mens should provide the temperature control necessary to
the specimens is applied as axially as possible. Perfect axial
satisfy the requirements specified in 9.4.
alignment is difficult to obtain especially when the pull rods
5.2.2 Heating shall be by an electric resistance or radiation
and extensometer rods pass through packing at the ends of the
furnace with the specimen in air at atmospheric pressure unless
furnace. However, the machine and grips should be capable of
other media are specifically agreed upon in advance.
loading a precisely made specimen so that the maximum
NOTE 2—The media in which the specimens are tested may have a
bending strain does not exceed 10 % of the axial strain, when
considerableeffectontheresultsoftests.Thisisparticularlytruewhenthe
the calculations are based on strain readings taken at zero force
properties are influenced by oxidation or corrosion during the test.
and at the lowest force for which the machine is being
5.3 Temperature-measuring system:
qualified.
5.3.1 The method of temperature measurement must be
NOTE 1—This requirement is intended to limit the maximum contribu-
sufficiently sensitive and reliable to ensure that the indicated
tion of the testing apparatus to the bending which occurs during a test. It
temperature of the specimen is within the limits specified in
is recognized that even with qualified apparatus different tests may have
quite different percent bending strain due to chance orientation of a 9.4.4.
loosely fitted specimen, lack of symmetry of that particular specimen,
5.3.2 Temperature should be measured with thermocouples
lateral force from furnace packing, and thermocouple wire, etc. The scant
as part of an appropriate temperature measuring system.
evidence available at this time indicates that the effect of bending strain
on test results is not sufficient, except in special cases, to require the
NOTE 3—Such measurements are subject to two types of error.
measurement of this quantity on each specimen tested.
Thermocouple calibration and instrument measuring errors initially intro-
duce uncertainty as to the exact temperature. Secondly both thermo-
5.1.2.1 In testing of brittle material even a bending strain of
couples and measuring instruments may be subject to variation with time.
10 % may result in lower strength than would be obtained with
Common errors encountered in the use of thermocouples to measure
improved axiality. In these cases, measurements of bending
temperatures include: calibration error, drift in calibration due to contami-
strain on the specimen to be tested may be specifically
nationordeteriorationwithuse,lead-wireerror,errorarisingfrommethod
of attachment to the specimen, direct radiation of heat to the bead,
requested and the permissible magnitude limited to a smaller
heat-conduction along thermocouple wires, etc.
value.
5.1.2.2 In general, equipment is not available for determin-
5.3.3 If temperature measurements are made using
ing maximum bending strain at elevated temperatures. The
thermocouples, those thermocouples shall be calibrated using
testing apparatus may be qualified by measurements of axiality
Practice E220. Representative thermocouples should be cali-
made at room temperature using the assembled machine, pull
brated from each lot of wires used for making base-metal
thermocouples. Except for relatively low temperatures of
exposure, base-metal thermocouples are subject to error upon
SubcommitteeE28.10onEffectofElevatedTemperatureonPropertiesrequests
factual information on the effect of nonaxiality of loading on test results. reuse,unlessthedepthofimmersionandtemperaturegradients
E21−20
of the initial exposure are reproduced. Consequently base- 5.4.4 To attach the extensometer to miniature specimens
metal thermocouples should be verified by the use of repre- may be impractical. In this case, separation of the specimen
sentative thermocouples and actual thermocouples used to holders or crossheads may be recorded and used to determine
measure specimen temperatures should not be verified at strains corresponding to the 0.2 % offset yield strength. The
elevated temperatures. Base-metal thermocouples also shall value so obtained is of inferior accuracy and must be clearly
not be reused without clipping back to remove wire exposed to marked as “approximate yield strength.” The observed exten-
the hot zone and rewelding or creating a new compression sionshouldbeadjustedbytheproceduredescribedin9.6.3and
junction. 10.1.3.
5.3.3.1 Noble metal thermocouples are also subject to errors 5.4.5 The extensometer system shall include a means of
due to contamination, etc., and should be periodically annealed determining strain rate.
and verified. Thermocouples should be kept clean prior to
5.5 Room-TemperatureControl—Unlesstheextensometeris
exposure and during use at elevated temperatures.
known to be insensitive to ambient temperature changes, the
5.3.3.2 Measurement of the emf drift in thermocouples
range of ambient temperature should not exceed 10 °F (6 °C)
during use is difficult. When drift is a problem during tests, a
while the extensometer is attached.The testing machine should
method should be devised to check the readings of the
not be exposed to perceptibly varying drafts.
thermocouples on the specimen during the test. For reliable
calibration of thermocouples after use the temperature gradient
6. Sampling
of the testing furnace must be reproduced during the recalibra-
6.1 Unless otherwise specified the following sampling pro-
tion.
cedures shall be followed:
5.3.4 The temperature-measuring system, shall be verified
6.1.1 Samples of the material to provide test specimens
yearly against a secondary standard, such as a precision
shallbetakenfromsuchlocationsastoberepresentativeofthe
potentiometer and if necessary re-calibrated. Extension-wire
lot from which it was taken.
error should be checked with the extension wires in place as
6.1.2 Samples shall be taken from material in the final
they normally are used.
condition (temper). One test shall be made on each lot.
5.4 Extensometer System:
6.1.3 A lot shall consist of all material from the same heat,
5.4.1 Practice E83, is recommended as a guide for selecting
nominal size, and condition (temper).
the required sensitivity and accuracy of extensometers. For
7. Test Specimens and Sample
determination of offset yield strength at 0.1 % or greater, a
Class B-2 extensometer may be used.The extensometer should
7.1 The size and shape of the test specimens should be
meet the requirements of Practice E83 and should, in addition,
based primarily on the requirements necessary to obtain
be tested to assure its accuracy when used in conjunction with
representative samples of the material being investigated.
a furnace at elevated temperature. One such test is to measure
7.2 Unless otherwise specified, test specimens shall be
at elevated temperature the stress and strain in the elastic range
oriented such that th
...
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.
´1
Designation: E21 − 17 E21 − 20
Standard Test Methods for
Elevated Temperature Tension Tests of Metallic Materials
This standard is issued under the fixed designation E21; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
ε NOTE—Section 3 was editorially updated in April 2019.
1. Scope*
1.1 These test methods cover procedure and equipment for the determination of tensile strength, yield strength, elongation, and
reduction of area of metallic materials at elevated temperatures.
1.2 Determination of modulus of elasticity and proportional limit are not included.
1.3 Tension tests under conditions of rapid heating or rapid strain rates are not included.
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.6 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:
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E8/E8M Test Methods for Tension Testing of Metallic Materials
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E74 Practices for Calibration and Verification for Force-Measuring Instruments
E83 Practice for Verification and Classification of Extensometer Systems
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
These test methods are under the jurisdiction of ASTM Committee E28 on Mechanical Testing and are the direct responsibility of Subcommittee E28.04 on Uniaxial
Testing.
Current edition approved Dec. 1, 2017Sept. 1, 2020. Published January 2018October 2020. Originally approved in 1933. Last previous edition approved in 20092017 as
ɛ1
E21 – 09.E21 – 17 . DOI: 10.1520/E0021-17E01.10.1520/E0021-20.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E21 − 20
E633 Guide for Use of Thermocouples in Creep and Stress-Rupture Testing to 1800°F (1000°C) in Air
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Definitions of terms relating to tension testing which appear in Terminology E6, apply to this test method. These terms include
alignment, axial strain, bending strain, gauge length, elongation, elongation after fracture, extensometer system, necking, reduction
of area, tensile strength, yield strength. In addition, the definitions of the following terms relating to tension testing are included.
3.1.1 Definitions of terms relating to tension testing which appear in E6, shall apply to the terms used in this test method.
3.2 Definitions:
3.2.1 reduced section,indicated temperature, n—the central portion of the specimen that has a cross section smaller than the
gripped ends.temperature indicated by the temperature-measuring system that meets the requirements of this standard.
3.2.1.1 Discussion—
The cross section is uniform within prescribed tolerances.
3.2.2 specified temperature—the test temperature requested by and reported to the customer.
3.2.3 length oftemperature-measuring system, the n—reduced section—the distance between the tangent points of the fillets that
bound the reduced section.a system consisting of one or more temperature-measuring transducers with the appropriate indicating
instruments, extension wires, reference junctions or ice points, and data acquisition devices.
3.2.3.1 Discussion—
The temperature-measuring transducer is usually a thermocouple.
3.2.3.2 Discussion—
The use of the term measuring system conforms to the definition of "measuring system” in the JCGM: International Vocabulary
of Metrology – Basic and General Concepts and Associated terms (VIM).
3.2.3 adjusted length of the reduced section—the length of the reduced section plus an amount calculated to compensate for strain
in the fillet region.
4. Significance and Use
4.1 The elevated-temperature tension test gives a useful estimate of the ability of metals to withstand the application of applied
tensile forces. Using established and conventional relationships it can be used to give some indication of probable behavior under
other simple states of stress, such as compression, shear, etc. The ductility values give a comparative measure of the capacity of
different materials to deform locally without cracking and thus to accommodate a local stress concentration or overstress; however,
quantitative relationships between tensile ductility and the effect of stress concentrations at elevated temperature are not universally
valid. A similar comparative relationship exists between tensile ductility and strain-controlled, low-cycle fatigue life under simple
states of stress. The results of these tension tests can be considered as only a questionable comparative measure of the strength
and ductility for service times of many hours. Therefore, the principal usefulness of the elevated-temperature tension test is to
assure that the tested material is similar to reference material when other measures such as chemical composition and
microstructure also show the two materials are similar.
5. Apparatus
5.1 Testing Machine:
5.1.1 The accuracy of the testing machine shall be within the permissible variation specified in Practices E4.
5.1.2 Precaution should be taken to assure that the force on the specimens is applied as axially as possible. Perfect axial alignment
is difficult to obtain especially when the pull rods and extensometer rods pass through packing at the ends of the furnace. However,
the machine and grips should be capable of loading a precisely made specimen so that the maximum bending strain does not exceed
10 % of the axial strain, when the calculations are based on strain readings taken at zero force and at the lowest force for which
the machine is being qualified.
NOTE 1—This requirement is intended to limit the maximum contribution of the testing apparatus to the bending which occurs during a test. It is
E21 − 20
recognized that even with qualified apparatus different tests may have quite different percent bending strain due to chance orientation of a loosely fitted
specimen, lack of symmetry of that particular specimen, lateral force from furnace packing, and thermocouple wire, etc. The scant evidence available
at this time indicates that the effect of bending strain on test results is not sufficient, except in special cases, to require the measurement of this quantity
on each specimen tested.
5.1.2.1 In testing of brittle material even a bending strain of 10 % may result in lower strength than would be obtained with
improved axiality. In these cases, measurements of bending strain on the specimen to be tested may be specifically requested and
the permissible magnitude limited to a smaller value.
5.1.2.2 In general, equipment is not available for determining maximum bending strain at elevated temperatures. The testing
apparatus may be qualified by measurements of axiality made at room temperature using the assembled machine, pull rods, and
grips used in highelevated temperature testing. The specimen form should be the same as that used during the elevated-temperature
tests and designed so that only elastic strains occur throughout the reduced section. This requirement may necessitate use of a
material different from that used during the elevated-temperature test. See Practice E1012 for recommended methods for
determining specimen alignment.
5.1.2.3 Gripping devices and pull rods may oxidize, warp, and creep with repeated use at elevated temperatures. Increased bending
stresses may result. Therefore, grips and pull rods should be periodically retested for axiality and reworked when necessary.
5.1.3 The testing machine shall be equipped with a means of measuring and controlling either the strain rate or the rate of
crosshead motion or both to meet the requirements in 9.6.
5.1.4 For high-temperatureelevated-temperature testing of materials that are readily attacked by their environment (such as
oxidation of metal in air), the specimen may be enclosed in a capsule so that it can be tested in a vacuum or inert gas atmosphere.
When such equipment is used, the necessary corrections must be made to determine the actual forces seen by the specimen. For
instance, compensation must be made for differences in pressures inside and outside of the capsule and for any variation in the
forces applied to the specimen due to sealing ring friction, bellows or other features.
5.2 Heating Apparatus:
5.2.1 The apparatus for and method of heating the specimens should provide the temperature control necessary to satisfy the
requirements specified in 9.4.
5.2.2 Heating shall be by an electric resistance or radiation furnace with the specimen in air at atmospheric pressure unless other
media are specifically agreed upon in advance.
NOTE 2—The media in which the specimens are tested may have a considerable effect on the results of tests. This is particularly true when the properties
are influenced by oxidation or corrosion during the test.
5.3 Temperature-Measuring Apparatus:Temperature-measuring system:
5.3.1 The method of temperature measurement must be sufficiently sensitive and reliable to ensure that the indicated temperature
of the specimen is within the limits specified in 9.4.4.
5.3.2 Temperature should be measured with thermocouples in conjunction with theas part of an appropriate temperature indicating
instrumentation.measuring system.
NOTE 3—Such measurements are subject to two types of error. Thermocouple calibration and instrument measuring errors initially introduce uncertainty
as to the exact temperature. Secondly both thermocouples and measuring instruments may be subject to variation with time. Common errors encountered
in the use of thermocouples to measure temperatures include: calibration error, drift in calibration due to contamination or deterioration with use, lead-wire
error, error arising from method of attachment to the specimen, direct radiation of heat to the bead, heat-conduction along thermocouple wires, etc.
5.3.3 Temperature measurements should be made with thermocouplesIf temperature measurements are made using thermocouples,
those thermocouples shall be calibrated using Practice E220of known calibration. . Representative thermocouples should be
calibrated from each lot of wires used for making base-metal thermocouples. Except for relatively low temperatures of exposure,
base-metal thermocouples are subject to error upon reuse, unless the depth of immersion and temperature gradients of the initial
Subcommittee E28.10 on Effect of Elevated Temperature on Properties requests factual information on the effect of nonaxiality of loading on test results.
E21 − 20
exposure are reproduced. Consequently base-metal thermocouples should be verified by the use of representative thermocouples
and actual thermocouples used to measure specimen temperatures should not be verified at elevated temperatures. Base-metal
thermocouples also shouldshall not be reused without clipping back to remove wire exposed to the hot zone and rewelding. Any
reuse of base-metal thermocouples after relatively low-temperature use without this precaution should be accompanied by
recalibration data demonstrating that calibration was not unduly affected by the conditions of exposure.rewelding or creating a new
compression junction.
5.3.3.1 Noble metal thermocouples are also subject to errors due to contamination, etc., and should be periodically annealed and
verified. Thermocouples should be kept clean prior to exposure and during use at elevated temperatures.
5.3.3.2 Measurement of the emf drift in thermocouples during use is difficult. When drift is a problem during tests, a method
should be devised to check the readings of the thermocouples on the specimen during the test. For reliable calibration of
thermocouples after use the temperature gradient of the testing furnace must be reproduced during the recalibration.
5.3.4 Temperature-measuring, controlling, and recording instruments should The temperature-measuring system, shall be verified
periodicallyyearly against a secondary standard, such as a precision potentiometer and if necessary re-calibrated. Lead-
wireExtension-wire error should be checked with the leadextension wires in place as they normally are used.
5.4 Extensometer System:
5.4.1 Practice E83, is recommended as a guide for selecting the required sensitivity and accuracy of extensometers. For
determination of offset yield strength at 0.1 % or greater, a Class B-2 extensometer may be used. The extensometer should meet
the requirements of Practice E83 and should, in addition, be tested to assure its accuracy when used in conjunction with a furnace
at elevated temperature. One such test is to measure at elevated temperature the stress and strain in the elastic range of a metal
of known modulus of elasticity. Combinations of stress and temperature which will result in creep of the specimen during the
extensometer sy
...
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