ASTM E235 / E235M - 12

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

    Active Standard ASTM E235 / E235M | Developed by Subcommittee: E20.04

    Book of Standards Volume: 14.03


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    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.

    This abstract is a brief summary of the referenced standard. It is informational only and not an official part of the standard; the full text of the standard itself must be referred to for its use and application. ASTM does not give any warranty express or implied or make any representation that the contents of this abstract are accurate, complete or up to date.

    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 DesignNominal 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.

    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 and health practices and determine the applicability of regulatory limitations prior to use.

    TABLE 1 Dimensions for Style G and U Measuring Junctions

    Sheath Outside Diameter, AMinimum
    Sheath
    Wall,
    B
    Minimum
    Insulation
    Thickness,
    C
    Minimum
    Wire
    Diameter,
    D
    E, ToleranceF, Tolerance
    NominalToleranceminmaxminmax
    minmax
    Inches
    0.04000.03900.04150.0060.0040.0050.0060.0200.0040.021
    0.06250.06150.06400.0090.0050.0100.0090.0320.0050.032
    0.12500.12400.12650.0120.0120.0200.0120.0620.0120.063
    0.18750.18650.18900.0200.0220.0310.0200.0930.0220.095
    0.25000.24800.25200.0300.0240.0400.0300.1250.0240.125
    [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


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    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 Practice for Liquid Penetrant Examination for General Industry

    E220 Test Method for Calibration of Thermocouples By Comparison Techniques

    E230 Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples

    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 Thermocouple 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 Metal-Sheathed Platinum Resistance Thermometers, Base Metal Thermocouples, and Noble Metal Thermocouples

    ANSI Standard

    B46.1 Surface Texture Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.

    American Welding Society Standard

    A5.9 Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel-Welding Rods and Bare Electrodes Available from American Welding Society (AWS), 550 NW LeJeune Rd., Miami, FL 33126, http://www.aws.org.


    ICS Code

    ICS Number Code 17.200.20 (Temperature-measuring instruments)

    UNSPSC Code

    UNSPSC Code 41112206(Thermocouples)


    DOI: 10.1520/E0235_E0235M-12

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