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.

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 Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.