ASTM E235/E235M-23

Standard Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other High-Reliability Applications

ABSTRACT
This specification covers the requirements for sheathed, Type K and N thermocouples for nuclear service. This specification can be used for sheathed thermocouples which are required for laboratory or general commercial applications where the environmental conditions exceed normal service requirements. The measuring junction styles for thermocouples are as follows: Style G2 (grounded) in which measuring junction is electrically connected to conductive sheaths and Style U2 (ungrounded) in which measuring junctions are electrically isolated from conductive sheaths and from reference ground. Different properties of the sheath such as integrity, cracks, voids, inclusions, surface finish, surface defect, and metallurgical structure shall be determined by performing different tests. Insulation resistance between thermoelements and the sheath shall be measured as well.
SCOPE
1.1 This specification covers the requirements for simplex, compacted mineral-insulated, metal-sheathed (MIMS), Type K and N thermocouples for nuclear or other high reliability service. Depending on size, these thermocouples are normally suitable for operating temperatures to 1652 °F [900 °C]; special conditions of environment and life expectancy may permit their use at temperatures in excess of 2012 °F [1100 °C]. This specification was prepared to detail requirements for this type of MIMS thermocouple for use in nuclear environments, but they can also be used for laboratory or general commercial applications where the environmental conditions exceed normal service requirements. The intended use of a MIMS thermocouple in a specific nuclear application will require evaluation of the compatibility of the thermocouple, including the effect of the temperature, atmosphere, and integrated neutron flux on the materials and accuracy of the thermoelements in the proposed application by the purchaser.  
1.2 This specification does not attempt to include all possible specifications, standards, etc., for materials that may be used as sheathing, insulation, and thermocouple wires for sheathed-type construction. The requirements of this specification include only the austenitic stainless steels and other alloys as allowed by Specification E585/E585M for sheathing, magnesium oxide or aluminum oxide as insulation, and Type K and N thermocouple wires for thermoelements (see Note 1).  
1.3 General Design—Nominal sizes of the finished thermocouples shall be 0.0400 in., 0.0625 in., 0.125 in., 0.1875 in., or 0.250 in. [1.000 mm, 1.500 mm, 3.000 mm, 4.500 mm, or 6.000 mm]. Sheath dimensions and tolerances for each nominal size shall be in accordance with Table 1 and Figs. 1 and 2. The measuring junction styles for thermocouples covered by this specification are as follows:  
FIG. 1 Grounded Measuring Junction, Style G  
FIG. 2 Ungrounded Measuring Junction, Style U  
1.3.1 Style G2  (grounded)—The measuring junction is electrically connected to its conductive sheath, and  
1.3.2 Style U2 (ungrounded)—The measuring junction is electrically isolated from its conductive sheath and from reference ground.  
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system are not exact equivalents or conversions; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the 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 Recomm...

General Information

• Status: Published
• Publication Date: 30-Jun-2023
• ICS: 17.200.20 - Temperature-measuring instruments
• Technical Committee: E20 - Temperature Measurement
• Drafting Committee: E20.12 - Thermocouples - Specifications

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: E235/E235M − 23 An American National Standard
Standard Specification for
Type K and Type N Mineral-Insulated, Metal-Sheathed
Thermocouples for Nuclear or for Other High-Reliability
1
Applications
This standard is issued under the fixed designation E235/E235M; 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.
2
1. Scope 1.3.1 Style G (grounded)—The measuring junction is elec-
trically connected to its conductive sheath, and
1.1 This specification covers the requirements for simplex,
2
1.3.2 Style U (ungrounded)—The measuring junction is
compacted mineral-insulated, metal-sheathed (MIMS), Type K
electrically isolated from its conductive sheath and from
and N thermocouples for nuclear or other high reliability
reference ground.
service. Depending on size, these thermocouples are normally
1.4 The values stated in either SI units or inch-pound units
suitable for operating temperatures to 1652 °F [900 °C]; spe-
are to be regarded separately as standard. The values stated in
cial conditions of environment and life expectancy may permit
each system are not exact equivalents or conversions;
their use at temperatures in excess of 2012 °F [1100 °C]. This
therefore, each system shall be used independently of the other.
specification was prepared to detail requirements for this type
Combining values from the two systems may result in non-
of MIMS thermocouple for use in nuclear environments, but
conformance with the standard.
they can also be used for laboratory or general commercial
applications where the environmental conditions exceed nor-
1.5 This standard does not purport to address all of the
mal service requirements. The intended use of a MIMS
safety concerns, if any, associated with its use. It is the
thermocouple in a specific nuclear application will require
responsibility of the user of this standard to establish appro-
evaluation of the compatibility of the thermocouple, including
priate safety, health, and environmental practices and deter-
the effect of the temperature, atmosphere, and integrated
mine the applicability of regulatory limitations prior to use.
neutron flux on the materials and accuracy of the thermoele-
1.6 This international standard was developed in accor-
ments in the proposed application by the purchaser.
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
1.2 This specification does not attempt to include all
Development of International Standards, Guides and Recom-
possible specifications, standards, etc., for materials that may
mendations issued by the World Trade Organization Technical
be used as sheathing, insulation, and thermocouple wires for
Barriers to Trade (TBT) Committee.
sheathed-type construction. The requirements of this specifi-
cation include only the austenitic stainless steels and other
2. Referenced Documents
alloys as allowed by Specification E585/E585M for sheathing,
3
2.1 ASTM Standards:
magnesium oxide or aluminum oxide as insulation, and Type K
A262 Practices for Detecting Susceptibility to Intergranular
and N thermocouple wires for thermoelements (see Note 1).
Attack in Austenitic Stainless Steels
1.3 General Design—Nominal sizes of the finished thermo-
E3 Guide for Preparation of Metallographic Specimens
couples shall be 0.0400 in., 0.0625 in., 0.125 in., 0.1875 in., or
E45 Test Methods for Determining the Inclusion Content of
0.250 in. [1.000 mm, 1.500 mm, 3.000 mm, 4.500 mm, or
Steel
6.000 mm]. Sheath dimensions and tolerances for each nominal
E112 Test Methods for Determining Average Grain Size
size shall be in accordance with Table 1 and Figs. 1 and 2. The
E165/E165M Practice for Liquid Penetrant Testing for Gen-
measuring junction styles for thermocouples covered by this
eral Industry
specification are as follows:
E220 Test Method for Calibration of Thermocouples By
1 2
This specification is under the jurisdiction of ASTM Committee E20 on Style G and Style U measuring junctions were previously termed Class 1 and
Temperature Measurement and is the direct responsibility of Subcommittee E20.12 Class 2 measuring junctions respectively.
3
on Thermocouples - Specifications. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved July 1, 2023. Published July 2023. Originally approved contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
in 1964. Last previous edition approve
...

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: E235/E235M − 19 E235/E235M − 23 An American National Standard
Standard Specification for
Type K and Type N Mineral-Insulated, Metal-Sheathed
Thermocouples for Nuclear or for Other High-Reliability
1
Applications
This standard is issued under the fixed designation E235/E235M; 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 specification covers the requirements for simplex, compacted mineral-insulated, metal-sheathed (MIMS), Type K and N
thermocouples for nuclear or other high reliability service. Depending on size, these thermocouples are normally suitable for
operating temperatures to 1652 °F [900 °C]; special conditions of environment and life expectancy may permit their use at
temperatures in excess of 2012 °F [1100 °C]. This specification was prepared to detail requirements for this type of MIMS
thermocouple for use in nuclear environments, but they can also be used for laboratory or general commercial applications where
the environmental conditions exceed normal service requirements. The intended use of a MIMS thermocouple in a specific nuclear
application will require evaluation of the compatibility of the thermocouple, including the effect of the temperature, atmosphere,
and integrated neutron flux on the materials and accuracy of the thermoelements in the proposed application by the purchaser.
1.2 This specification does not attempt to include all possible specifications, standards, etc., for materials that may be used as
sheathing, insulation, and thermocouple wires for sheathed-type construction. The requirements of this specification include only
the austenitic stainless steels and other alloys as allowed by Specification E585/E585M for sheathing, magnesium oxide or
aluminum oxide as insulation, and Type K and N thermocouple wires for thermoelements (see Note 1).
1.3 General Design—Nominal sizes of the finished thermocouples shall be 0.0400 in., 0.0625 in., 0.125 in., 0.1875 in., or 0.250
in. [1.000 mm, 1.500 mm, 3.000 mm, 4.500 mm, or 6.000 mm]. Sheath dimensions and tolerances for each nominal size shall be
in accordance with Table 1 and Figs. 1 and 2. The measuring junction styles for thermocouples covered by this specification are
as follows:
2
1.3.1 Style G (grounded)—The measuring junction is electrically connected to its conductive sheath, and
2
1.3.2 Style U (ungrounded)—The measuring junction is electrically isolated from its conductive sheath and from reference
ground.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system are not exact equivalents or conversions; therefore, each system shall be used independently of the other. Combining values
from the two systems may result in non-conformance with the standard.
1
This specification is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.12 on
Thermocouples - Specifications.
Current edition approved May 1, 2019July 1, 2023. Published May 2019July 2023. Originally approved in 1964. Last previous edition approved in 20182019 as
E235/E235M – 12 (2018).E235/E235M – 19. DOI: 10.1520/E0235_E0235M-19.10.1520/E0235_E0235M-23.
2
Style G and Style U measuring junctions were previously termed Class 1 and Class 2 measuring junctions respectively.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
1

---------------------- Page: 1 ----------------------
E235/E235M − 23
TABLE 1 Dimensions for Style G and U Measuring Junctions
Minimum Minimum Minimum
Sheath Outside Diameter, A E, Tolerance F, Tolerance
Sheath Insulation Wire
Wall, Thickness, Diameter,
Tolerance
BWall, CThickness, DDiameter,
Nominal min max min max
min max B C D
Inches
0.0400 0.0390 0.0415 0.006 0.004 0.005 0.006 0.020 0.004 0.021
0.0625 0.0615 0.0640 0.009 0.005 0.010 0.009 0.032 0.005 0.032
0.1250 0.1240 0.1265 0.012 0.012 0.020 0.012 0.062 0.012 0.063
0.1875 0.1865 0.1890 0.020 0.022 0.031 0.020 0.093 0.022 0.095
0.2500 0.2480 0.2520 0.030 0.024 0.040 0.030 0.125 0.024 0.125
[Millimetres]
[1.000] [0.975] [1.038] [0.15] [0.10] [0.13] [0.15] [0.51] [0.10] [0.53]
[1.500] [1.475] [1.538] [0.23] [0.13] [0.25] [0.23] [0.81] [0.13] [0.81]
[3.000] [2.975] [3.038] [0.30] [0
...