ASTM E235/E235M-23

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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
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:
1.3.1 Style G (grounded)—The measuring junction is electrically connected to its conductive sheath, and
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.
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.
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
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] [0.30] [0.51] [0.30] [1.57] [0.30] [1.60]
[4.500] [4.475] [4.538] [0.51] [0.56] [0.79] [0.51] [2.36] [0.56] [2.41]
[6.000] [5.950] [6.050] [0.76] [0.61] [1.02] [0.76] [3.18] [0.61] [3.18]
FIG. 1 Grounded Measuring Junction, Style G
FIG. 2 Ungrounded Measuring Junction, Style U
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:
A262 Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
E3 Guide for Preparation of Metallographic Specimens
E45 Test Methods for Determining the Inclusion Content of Steel
E112 Test Methods for Determining Average Grain Size
E165/E165M Practice for Liquid Penetrant Testing for General Industry
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230/E230M Specification for Temperature-Electromotive Force (emf) Tables for Standardized Thermocouples
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.
E235/E235M − 23
E344 Terminology Relating to Thermometry and Hydrometry
E585/E585M Specification for Compacted Mineral-Insulated, Metal-Sheathed, Base Metal Thermocouple Cable
E780 Test Method for Measuring the Insulation Resistance of Mineral-Insulated, Metal-Sheathed Thermocouples and
Mineral-Insulated, Metal-Sheathed Cable at Room Temperature
E839 Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Cable
E883 Guide for Reflected–Light Photomicrography
E1652 Specification for Magnesium Oxide and Aluminum Oxide Powder and Crushable Insulators Used in the Manufacture of
Base Metal Thermocouples, Metal-Sheathed Platinum Resistance Thermometers, and Noble Metal Thermocouples
2.2 ANSI Standard:
B46.1 Surface Texture
2.3 American Welding Society Standard:
A5.9 Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel-Welding Rods and Bare Electrodes
3. Terminology
3.1 The definitions given in Terminology E344 shall apply to this specification.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 lot, n—a quantity of finished MIMS thermocouples manufactured from the same lot of MIMS cable, then assembled and
processed at the same time under the same controlled production conditions to their required final configuration.
4. Ordering Information and Basis of Purchase
4.1 The purchase order documents shall specify the following information:
4.1.1 The quantity, length, and nominal diameter of the MIMS thermocouple,
4.1.2 The thermocouple type and tolerance on the initial values of emf versus temperature per Table 2, if other than standard,
4.1.3 The type of ceramic insulation required, either alumina (Al O ) or magnesia (MgO),
2 3
4.1.4 The type of sheath material and other information required (see 5.1.1),
4.1.5 The style of thermocouple measuring junction (see 1.2),
4.1.6 The type of dye-penetrant inspection procedure to be used, and
TABLE 2 Tolerances on Initial Values of EMF versus Temperature for MIMS Thermocouples
NOTE 1—Tolerances in this table apply to new MIMS thermocouples.
NOTE 2—Tolerances apply to new material as produced and do not allow for changes in thermoelectric characteristics of the materials during use. The
magnitude of such changes depends upon such factors as sheath and thermoelement size, temperature, time of exposure, and the environment.
NOTE 3—Where tolerances are given in percent, the percentage applies to the temperature being measured when expressed in degrees Celsius.
NOTE 4—To determine the tolerance in degrees Fahrenheit, multiply the tolerance in degrees Celsius by 9/5.
Tolerances—Reference Junction 32 °F [0 °C]
Thermocouple Temperature Range
Standard Tolerances Special Tolerances
Type
°F [°C] °F [°C] °F [°C]
K or N 32 to 2300 [0 to 1260] Note 4 [The greater of ±2.2 °C or Note 4 [The greater of ±1.1 °C or ±0.4 %]
±0.75 %]
A B
K –328 to 32 [–200 to 0] [The greater of ±2.2 °C or ±2 %]
A
MIMS the thermocouples are normally supplied to meet the tolerances specified in the table for temperatures above 0 °C. The same materials, however, may not fall
within the sub-zero tolerances given in the second section of the table. If materials are required to meet the sub-zero limits, the purchase order shall so state. Selection
of materials shall be required.
B
Little information is available to justify establishing special tolerances for sub-zero temperatures. Such special sub-zero tolerances, if required, shall be agreed upon
between the purchaser and the producer.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Available from American Welding Society (AWS), 550 NW LeJeune Rd., Miami, FL 33126, http://www.aws.org.
E235/E235M − 23
4.1.7 Any deviations from this specification or the referenced specifications.
5. Materials and Manufacture
5.1 All materials used shall be in accordance with the following requirements:
5.1.1 Sheath Materials—The sheath material used for the thermocouples described in this specification shall meet the requirements
of Specification E585/E585M. The purchaser of the thermocouples shall specify only the name of the material (seamless or
welded), grade, optional requirements, test report required, and ASTM designation.
5.1.1.1 The inclusion level of the sheath shall be determined by mounting a 1-in. minimum length of a longitudinal section of the
sheath using Test Methods E45, Microscopical Method A, for examination. The inclusion level shall be less than 3 A through D,
thin or heavy.
5.1.1.2 The grain size of the sheath shall be determined by a specimen taken in accordance with Test Methods E112. Grain size
shall be as specified in Table 3, or finer, as determined by the Comparison Procedure of Test Methods E112.
5.1.1.3 Each lot of sheath material used shall be sampled using Practices A262 as follows. Samples shall be tested by Practice A,
and further tested as outlined by Table 1 in Practices A262, where screening tests so indicate. Acceptance levels for these tests shall
be agreed upon between the purchaser and the producer.
5.1.2 Thermoelement—Thermoelements referred to in this specification shall be Type K or Type N with a standard tolerance on
initial values of emf versus temperature as specified in Table 2 unless otherwise specified by the purchaser.
NOTE 1—The purchaser may specify an alternative type of thermoelement as designated in Specification E230/E230M by indicating this deviation in the
ordering documents. The supplier and the purchaser shall then agree upon a tolerance.
5.1.3 Insulation—The insulating material shall be either magnesia (MgO) or alumina (Al O ) and shall comply with Specification
2 3
E1652 Type 1P material requirements:
5.1.3.1 A certified analysis of the composition of the insulating material as supplied to the thermocouple manufacturer shall be
furnished to the purchaser. The thermocouple manufacturer shall be responsible for maintaining the purity in the finished product
within the specified limits.
5.1.4 Welding Rod—Filler rod material used for welding on the sheath or for welding the end of the thermocouple closed shall
comply with the requirements of AWS Specification A5.9 for the sheath material specified on the ordering documents.
5.2 Processing:
5.2.1 Cleanliness—The outer surface of the completed thermocouples at the time of delivery shall be free of residues containing
nuclear poisons (such as boron and cadmium compounds) or foreign substances (such as chlorine compounds, strong acids or
bases, oils, greases, or dust) that could become the source of corrosion or chemistry changes in a primary coolant or heat-transfer
medium. The use of compounds containing halogens for final cleaning is prohibited. Alcohol, or methyl isobutyl ketone may be
used unless otherwise specified.
5.2.2 Annealing—The sheath of the finished thermocouple shall be solution annealed and shall not be sensitized.
TABLE 3 Maximum Grain Sizes
Sheath Outside Diam
...