ASTM E608 – E 608M – 00 R04

Designation: E 608/E 608M – 00 (Reapproved 2004) Standard Specification for Mineral-Insulated, Metal-Sheathed Base Metal Thermocouples1 This standard is issued under the fixed designation E 608/E 608M; 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 (e) indicates an editorial change since the last revision or reapproval. 1. Scope 1.1 This specification covers the requirements for mineral- insulated, metal-sheathed base metal thermocouples for indus- trial or high-reliability applications. It applies specifically to thermocouples fabricated from sheathed thermocouple mate- rial in accordance with Specification E 585/E 585M. Provi- sions are made for selecting thermoelements, insulation, and sheath material, and measuring junction configuration, thermo- couple assembly length, and the type of transition or termina- tion. 1.2 This specification also includes provisions for quality assurance or verification program requirements, or both, as a purchaser’s option. 1.3 The values stated in SI (metric) units or inch-pound units may be regarded separately as the standard. The values stated in each system are not the exact equivalents, and each system shall be used independently of the other. 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 appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: 2 E 94 Guide for Radiographic Examination E 142 Method for Controlling Quality of Radiographic Testing3 E 165 Test Method for Liquid Penetrant Examination E 220 Test Method for Calibration of Thermocouples by Comparison Techniques E 230 Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples E 344 Terminology Relating to Thermometry and Hydrom- etry E 585/E 585M Specification for Compacted Mineral- Insulated, Metal-Sheathed, Base Metal Thermocouple Cable E 780 Test Method for Measuring the Insulation Resistance of Sheathed Thermocouple Material at Room Temperature E 839 Test Methods for Sheathed Thermocouples and Sheathed Thermocouple Material 2.2 AWS Standards:4 A5.9 Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel Welding Rods and Bare Elec- trodes A5.14 Specification for Nickel and Nickel-Alloy Bare Welding Rods and Electrodes 3. Terminology 3.1 Definitions—The definitions given in Terminology E 344 shall apply to this specification. 3.2 Definitions of Terms Specific to This Standard: 3.2.1 common ungrounded junction, n—measuring junc- tions within the same multi-pair thermocouple that are electri- cally isolated from the sheath but electrically connected to each other. 3.2.2 isolated ungrounded junction, n—measuring junctions within the same multi-pair thermocouple that are electrically isolated from the sheath and electrically isolated from each other. 3.2.3 lot, n—a quantity of thermocouples manufactured from the same continuous length of mineral-insulated, metal- sheathed thermocouple cable. 3.2.4 sheathed thermocouple material, n—a combination of two or more continuous thermoelements embedded in ceramic insulation compacted within a metal protecting sheath. 1 This specification is under the jurisdiction of ASTM Committee E20 on Temperature Measurement and is the direct responsibility of Subcommittee E20.04 on Thermocouples. Current edition approved May 1, 2004. Published June 2004. Originally approved in 1977. Last previous edition approved in 2000 as E 608/E 608M - 00. 2 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. 3 Withdrawn. 4 Available from The American Welding Society (AWS), 550 NW LeJeune Rd., Miami, FL 33126. 1 Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 4. Significance and Use 4.1 This specification describes the physical requirements of mineral-insulated, metal-sheathed base metal thermocouples and establishes suitable test criteria for them. 4.2 Standardized dimensional requirements, including ac- ceptable allowances for manufacturing variations, are given. 4.3 A set of standard tests to be applied to all thermocouples covered by this specification are described together with a group of optional tests from which applicable additional requirements may be selected. 4.4 Warning—Users should be aware that certain charac- teristics of thermocouples might change with time and use. If a thermocouple’s designed shipping, storage, installation, or operating temperature has been exceeded, the thermocouple’s moisture seal may have been compromised and may no longer adequately prevent the deleterious intrusion of water vapor. Consequently, the thermocouple’s condition established by test at time of manufacture may not apply later during an extended period of use, and retesting may become necessary. In addition, inhomogeneities can develop in thermoelements because of exposure to temperature, even in cases where maximum exposure temperatures have been lower than the suggested upper temperature limits of Table 1. For this reason, calibration of thermocouples destined for delivery to a customer is not recommended (see S6.1). Because the EMF indication of any thermocouple depends upon the condition of the thermoele- ments along their entire length, as well as the temperature profile pattern in the region of any inhomogeneity, the EMF output of a used thermocouple will be unique to its installation. Because temperature profiles in calibration equipment are unlikely to duplicate those of the installation, removal of a used thermocouple to a separate apparatus for calibration is not recommended. Instead, in situ calibration by comparison to a similar thermocouple known to be good is often recommended. 5. Ordering Information 5.1 The purchase documents shall specify the following options: 5.1.1 The type and quantity of thermoelement pairs, and the tolerances, if other than standard (see 6.4 and 6.5). 5.2 The nominal sheath diameter. See Table 1 or Specifica- tion E 585/E 585M for preferred nominal diameters. 5.3 The type of ceramic insulation (MgO or Al2O3). See Specification E 585/E 585M. 5.4 The type of sheath material. See Table 2 or Specification E 585/E 585M. 5.5 The type of measuring junction, Class 1 (grounded) or Class 2 (ungrounded). See Figs. 1 and 2. If more than one pair of thermoelements is specified, Class 2 is further subdivided into Class 2A (common ungrounded) and Class 2B (isolated ungrounded). Do not specify Class 1 grounded junctions with Type T thermoelements (see 6.3.2). 5.6 The quantity, length, and length tolerance of each thermocouple. See Figs. 3-6 for examples. 5.7 The type and configuration of connection head, connec- tor, transition piece, or termination, and moisture seal required on the end opposite the measuring junction. See Figs. 3-6 for examples. The minimum and maximum intended operating temperature of the connection head, transition, or termination, and moisture seal should be specified (6.6). For thermocouples with insulated wire attached (Fig. 6) and Class 2 junctions, state the minimum acceptable insulation resistance (6.7). 5.8 Optional supplementary testing requirements and test sample rate (8.2). 5.9 The quality assurance or verification program require- ments, or both, including material traceability if required. See Appendix X1. 5.10 Any deviations from this specification or the refer- enced specifications. TABLE 1 Suggested Upper Temperature Limits for Sheathed Thermocouples NOTE 1—This table gives the suggested upper temperature limits for the various thermocouples in several common sheath sizes. It does not take into account environmental temperature limitations of the sheath material itself, nor does it address compatibility considerations between the thermoelement materials and the sheath containing them. The actual maximum practical temperature in a particular situation will generally be limited to the lowest temperature among the several factors involved. The purchaser should consult ASTM Manual 125 and other literature sources for further applications information. NOTE 2—The temperature limits given here are intended only as a guide to the purchaser and should not be taken as absolute values nor as guarantees of satisfactory life or performance. These types and sizes are sometimes used at temperatures above the given limits, but usually at the expense of stability or life, or both. In other instances, it may be necessary to reduce the given limits in order to achieve adequate service. Upper Temperature Limit for Various Sheath Diameters °C [°F] Nominal Sheath Diameter Thermocouple Type mm in. T J E K, N 0.5 0.020 260 (500) 260 (500) 300 (570) 700 (1290) . . . 0.032 260 (500) 260 (500) 300 (570) 700 (1290) 1.0 0.040 260 (500) 260 (500) 300 (570) 700 (1290) 1.5 0.062 260 (500) 440 (825) 510 (950) 920 (1690) 2.0 . . . 260 (500) 440 (825) 510 (950) 920 (1690) . . . 0.093 260 (500) 480 (900) 580 (1075) 1000 (1830) 3.0 0.125 315 (600) 520 (970) 650 (1200) 1070 (1960) 4.5 0.188 370 (700) 620 (1150) 730 (1350) 1150 (2100) 6.0 0.250 370 (700) 720 (1330) 820 (1510) 1150 (2100) 8.0 0.375 370 (700) 720 (1330) 820 (1510) 1150 (2100) E 608/E 608M – 00 (2004) 2 5.11 Shipping method and straightness criteria, if required (see 10.2).5 5.12 The minimum and maximum intended operating tem- peratures of the thermocouple (see S6.1). 6. General Requirements 6.1 Tagging—During fabrication, each thermocouple shall be tagged with a unique identification number to keep trace- ability to materials and test data. The producer’s standard tagging method may be used. 6.2 Welding Rod—Filler material used for welding or plug- ging the end closure shall comply with Table 2. 6.3 Measuring Junctions: 6.3.1 The end closure shall be impervious to gases and liquids. There shall be no cracks, holes, or void defects that penetrate through the metal wall. Any mineral oxide removed during fabrication of the measuring junction shall be replaced with dry oxide of the same type that is in accordance with the purity requirements of Specification E 585/E 585M. Class 2 measuring junctions shall be fabricated by welding the ther- moelements without filler metal or flux. 6.3.2 The measuring junction end closures shall be seal welded. The use of plugs or filler metals is optional. Class 1 (grounded) measuring junctions on Type T thermocouples are excluded from this specification because of the problems associated with welding the copper thermoelement. 6.4 Standard Tolerances—Sheathed thermocouples fabri- cated to this specification shall conform to the standard tolerances (see Table 3) in accordance with Specification E 230, unless otherwise specified. 6.5 Special Tolerances—If specified in the purchase docu- ment, the special tolerances (see Table 3) in accordance with Specification E 230 shall apply. 6.6 Termination—The sheathed thermocouples shall be ter- minated at the end opposite the measuring junction in a manner specified by the purchaser. All exposed MgO or Al2O3 shall be sealed from moisture to keep the insulation dry. All connectors, connection heads, or transitions shall include a positive method of preventing strain on the thermoelements emerging from the sheathed material. All transitional wire connections shall be brazed or welded. The moisture seal and termination (see Figs. 3-6) shall be compatible with their intended installation and operating conditions (see 5.7). 6.7 Room Temperature Insulation Resistance (Class 2 Junctions)—The minimum room temperature electrical insula- tion resistance between the thermoelement pairs and the sheath for sheathed thermocouples with Class 2 junctions shall be as specified in Table 4 for the dc test voltage noted. In addition, for Class 2B (isolated ungrounded) junctions, the minimum electrical insulation specified in Table 4 shall also apply between thermoelement pairs. The minimum insulation value shall be negotiated between the purchaser and the producer for Fig. 6 assemblies with purchaser-specified insulated thermo- couple extension wire or other devices attached. For Fig. 5 assemblies, the minimum insulation resistance values of Table 4 shall be imposed before the thermocouple is terminated (when it is like Fig. 4). The insulation resistance shall be tested in accordance with Test Method E 780. 6.8 Sheath Condition—The surface of the completed ther- mocouples shall be visually clean, dry, and oxide-free. 6.9 The tests specified in 8.1 are required to determine if the specification requirements have been met. Additional optional requirements are listed in the Supplementary Requirements section, and may be included in the purchase order require- ments, as desired by the purchaser. 6.10 All testing and inspection shall be performed in accor- dance with Test Methods E 839 unless otherwise indicated. 7. Measuring Junction Configuration 7.1 The measuring junction configurations are shown in cross section in Figs. 1 and 2. The tip shape is optional as long as the dimensional requirements are maintained. The preferred nominal sheath diameters are listed in Table 1 or Specification E 585/E 585M. The measuring junction dimensional require- ments are as follows: 7.1.1 Dimension A, End-Closure Diameter, Classes 1 and 2—The end-closure maximum diameter shall be no larger than the nominal sheath diameter plus a weld allowance of 0.05 mm (0.002 in.) or 2 % of the nominal sheath diameter, whichever is larger. Localized reduction of the end-closure diameter caused by weld shrinkage shall not exceed 0.05 mm (0.002 in.) or 2 % of the nominal sheath diameter, whichever is larger. This expanded end-closure diametral tolerance shall apply from the tip of the end closure over a length not exceeding 23 the nominal sheath diameter. 7.1.2 Dimensions Controlled by Supplementary Radio- graphic Inspection (see Supplementary Requirement S1): 7.1.2.1 Dimension B, Measuring Junction Length—The measuring junction length on Class 2A and Class 2B junctions shall be a minimum of one and a maximum of four thermo- element diameters long. 7.1.2.2 Dimension C, Minimum Measuring Junction Insula- tion Thickness, Radial Dimension—The minimum insulation thickness on Class 2A and 2B junctions, as measured from the junction to the sheath in a radial direction, shall be 5 % of the nominal sheath diameter. 7.1.2.3 Dimension D, Minimum Material Thickness, Class 1 and Class 2 Junctions—The thickness at any point of the end-closure weld interface shall be not less than 10 % of the nominal sheath diameter. Wall thinning caused by welding 5 “Manual on the Use of Thermocouples in Temperature Measurement,” ASTM Manual 12, ASTM International, 1993. TABLE 2 Weld Closure Filler Metal Sheath Material Weld Rod AWSType AWS Specifica- tion Austenitic Stainless Steels TP 304 ER 308 A5.9 TP 304L ER 308L A5.9 TP 310 ER 310 A5.9 TP 316 ER 316 A5.9 TP 316L ER 316L A5.9 TP 317 ER 317 A5.9 TP 321 ER 347 A5.9 TP 347 ER 347 A5.9 TP 348 ER 348 A5.9 Nickel-chromium-iron alloy ER NiCrFe-5 A5.14 E 608/E 608M – 00 (2004) 3 shall be limited to the minimum material sheath wall thickness requirement of 10 % of the nominal diameter. 7.1.2.4 Dimension E, End-Closure Thickness—The end- closure thickness, on both Class 1 and Class 2 junctions, shall be a minimum of 10 % and a maximum of 80 % of the nominal sheath diameter. 7.1.2.5 Dimension F, Measuring Junction Location—The measuring junction or junctions of Class 2A and 2B thermo- couples, respectively, shall be located a minimum of 10 % of the sheath diameter and a maximum of either 0.75 mm (0.030 in.) or 50 % of the nominal sheath diameter, whichever is greater, from the inside surface of the end closure. Dimension F is defined as the shortest axial distance between end closure and measuring junction. FIG. 1 Grounded Measuring Junction, Class 1 FIG. 2 Ungrounded Measuring Junction, Class 2 FIG. 3 Sheathed Thermocouple FIG. 4 Sheathed Thermocouple with Exposed Wires FIG. 5 Sheathed Thermocouple Assembly with Connector or Connection Head (Any Type Specified) FIG. 6 Sheathed Thermocouple Assembly with Transition Piece E 608/E 608M – 00 (2004) 4 8. Test Requirements 8.1 Standard Tests—There are certain minimum inspection requirements for each thermocouple fabricated to this specifi- cation. Perform the standard tests in accordance with the producer’s established procedures in accordance with 8.4. These tests, noted as standard tests, are listed as follows: 8.1.1 Visual and Envelope Dimensional Inspection, 8.1.2 Room Temperature Insulation Resistance Measure- ment on Class 2 Junctions Only, 8.1.3 Thermocouple Polarity Test, and 8.1.4 Electrical Continuity Test. 8.2 Optional Tests—The optional tests listed below may be specified in whole or part in the purchase documents by the purchaser. The sample rate shall also be specified by the purchaser. Perform the optional tests in accordance with the following Supplementary Requirements: S1—Radiographic Inspection S2—End-Closure Weld Integrity Test Using the Dye Pen- etrant Method S3—End-Closure Weld and Sheath Integrity Test Using the Helium Mass Spectrometer Method S4—End-Closure Weld and Sheath Integrity Test Using Water (thermocouples with Class 2 measuring junctions only) S5—Elevated Temperature Insulation Resistance (thermo- couples with Class 2 measuring junctions only) S6—Calibration 8.3 Documentation—Copies of the documented test results shall be supplied to the purchaser, along with a certification of conformance in accordance with Section 9. 8.4 Standard Tests—The producer shall perform the follow- ing measurements and checks on each thermocouple, using the test and inspection methods described in Test Methods E 839 to ensure that the product conforms to the ordering documents. 8.4.1 Visual and Envelope Dimensional Inspection— Examine each thermocouple to ensure that the length is within the length tolerance ordered, and that the connector or termi- nation is of the type, size, or configuration, or a combination of these, specified. Examine each thermocouple to ensure that a moisture seal is present, that the measuring junction end- closure weld is within dimensional limits, and that surface finish, straightness, and cleanliness are acceptable. 8.4.2 Room-Temperature Insulation Resistance—Measure the insulation resistance of each Class 2 (ungrounded) thermo- couple between all thermoelements and sheath for conform- ance with Table 4 with the applied voltage specified (both direct and reversed polarity). In addition, measure the insula- tion resistance of each Class 2B (isolated ungrounded) ther- mocouple between thermoelement pairs for conformance with Table 4 with the applied voltage specified (both direct and reversed polarity). Document measured values. Measure Class 2 thermocouples with thermocouple extension wire attached (Fig. 6) before and after attachment. Use the values measured prior to termination to judge conformance. The values mea- sured after termination shall exceed the values agreed upon between the purchaser and the producer. This test can also apply to Class 1 (grounded junction) thermocouples if both producer and purchaser agree that the purchaser can select a sample thermocouple from the lot, remove the junction, exercising caution to prevent moisture pick-up, and measure insulation resistance. In the event that this sample thermo- couple has insulation resistance less than that speci