ASTM-E235 Standard Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other High-Reliability Applications

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



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1.1 Intent- This specification presents the requirements for sheathed, Type K thermocouples for nuclear 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 specifically to detail requirements for using this type of sheathed thermocouple in nuclear environments. 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 intended use of a sheathed thermocouple in a specific nuclear application will require evaluation, by the purchaser, 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. 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 for sheathing, magnesium oxide or aluminum oxide as insulation, and Type K thermocouple wires for thermoelements (see Note 2).

1.2 General Design- Nominal sizes of the finished thermocouples shall be 0.0400 in. (1.016 mm), 0.0625 in. (1.588 mm), 0.1875 in. (4.763 mm), 0.125 in. (3.175 mm), or 0.250 in. (6.350 mm). Sheath dimensions and tolerances for each nominal size shall be in accordance with Table 1. The classes of thermocouples covered by this specification are as follows:

1.2.1 Class 1- Measuring junction grounded to sheath, and

1.2.2 Class 2- Measuring junction not grounded to sheath (insulated junction).

1.2.3 See Figs. 1 and 2 and Table 1 for details.

Note 1-The values stated in inch-pound units are to be regarded as the standard.


grounded junction; high-reliability thermocouple; insulated junction; metal-sheathed; mineral insulated; thermocouple; ICS Number Code 17.200.20 (Temperature-measuring instruments)

To find similar documents by ASTM Volume:

14.03 (Temperature Measurement)

To find similar documents by classification:

17.200.20 (Temperature-measuring instruments Including thermostats Medical thermometers, see 11.040.55)

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Editorially changed

Publication Date

July 12, 2023

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Page Count

6 pages

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