ASTM E235

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 sheathed, Type K and N 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 and other alloys as allowed with Specification E 585/E 585M for sheathing, magnesium oxide or aluminum oxide as insulation, and Type K and N thermocouple wires for thermoelements (see Note 1).

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

1.2.1 Style G (grounded) Measuring junction electrically connected to conductive sheaths, and

1.2.2 Style U (ungrounded) Measuring junctions are electrically isolated from conductive sheaths and from reference ground.

1.3 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.

1.4 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.

2. Referenced Documents

A262 Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
E112 Test Methods for Determining Average Grain Size
E165 Test Method for Liquid Penetrant Examination
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
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230 Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples
E3 Guide for Preparation of Metallographic Specimens
E344 Terminology Relating to Thermometry and Hydrometry
E45 Test Methods for Determining the Inclusion Content of Steel
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 Material
E883 Guide for Reflected-Light Photomicrography
E94 Guide for Radiographic Examination
A5.9 Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel-Welding Rods and Bare Electrodes
B46.1 Surface Texture

Index Terms

grounded junction; high-reliability thermocouple; metal-sheathed; mineral insulated; thermocouple ; ungrounded junction; ICS Number Code 17.200.20

Citing ASTM Standards

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