ASTM E608/E608M-00
(Specification)Standard Specification for Mineral-Insulated, Metal-Sheathed Base-Metal Thermocouples
Standard Specification for Mineral-Insulated, Metal-Sheathed Base-Metal Thermocouples
SCOPE
1.1 This specification covers the requirements for mineral-insulated, metal-sheathed base metal thermocouples for industrial or high-reliability applications. It applies specifically to thermocouples fabricated from sheathed thermocouple material conforming to Specification E 585/E 585M. Provisions are made for selecting thermoelements, insulation, and sheath material, and measuring junction configuration, thermocouple assembly length, and the type of transition or termination.
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 appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E 608/E 608M – 00
Standard Specification for
Mineral-Insulated, Metal-Sheathed Base Metal
Thermocouples
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 Insulated, Metal-Sheathed, Base Metal Thermocouple
Cable
1.1 This specification covers the requirements for mineral-
E 780 Test Method for Measuring the Insulation Resistance
insulated, metal-sheathed base metal thermocouples for indus-
of Sheathed Thermocouple Material at Room Temperature
trial or high-reliability applications. It applies specifically to
E 839 Test Methods for Sheathed Thermocouples and
thermocouples fabricated from sheathed thermocouple mate-
Sheathed Thermocouple Material
rial conforming to Specification E 585/E 585M. Provisions are
2.2 AWS Standards:
made for selecting thermoelements, insulation, and sheath
A5.9 Specification for Corrosion-Resisting Chromium and
material, and measuring junction configuration, thermocouple
Chromium-Nickel Steel Welding Rods and Bare Elec-
assembly length, and the type of transition or termination.
trodes
1.2 This specification also includes provisions for Quality
A5.14 Specification for Nickel and Nickel-Alloy Bare
Assurance or Verification Program Requirements, or both, as a
Welding Rods and Electrodes
purchaser’s option.
1.3 The values stated in SI (metric) units or inch-pound
3. Terminology
units may be regarded separately as the standard. The values
3.1 Definitions—The definitions given in Terminology
stated in each system are not the exact equivalents, and each
E 344 shall apply to this specification.
system shall be used independently of the other.
3.2 Definitions of Terms Specific to This Standard:
1.4 This standard does not purport to address all of the
3.2.1 common ungrounded junction, n—measuring junc-
safety concerns, if any, associated with its use. It is the
tions within the same multi-pair thermocouple that are electri-
responsibility of the user of this standard to establish appro-
cally isolated from the sheath but electrically connected to each
priate safety and health practices and determine the applica-
other.
bility of regulatory limitations prior to use.
3.2.2 isolated ungrounded junction, n—measuring junctions
2. Referenced Documents within the same multi-pair thermocouple that are electrically
isolated from the sheath and electrically isolated from each
2.1 ASTM Standards:
other.
E 94 Guide for Radiographic Testing
3.2.3 lot, n—a quantity of thermocouples manufactured
E 142 Method for Controlling Quality of Radiographic
from the same continuous length of mineral-insulated, metal-
Testing
2 sheathed thermocouple cable.
E 165 Test Method for Liquid Penetrant Examination
3.2.4 sheathed thermocouple material, n—a combination of
E 220 Test Method for Calibration of Thermocouples by
4 two or more continuous thermoelements embedded in ceramic
Comparison Techniques
insulation compacted within a metal protecting sheath.
E 230 Specification and Temperature-Electromotive Force
(EMF) Tables for Standardized Thermocouples
4. Significance and Use
E 344 Terminology Relating to Thermometry and Hydrom-
4.1 This specification describes the physical requirements of
etry
mineral-insulated, metal-sheathed base metal thermocouples
E 585/E 585M Specification for Compacted Mineral-
and establishes suitable test criteria for them.
4.2 Standardized dimensional requirements, including ac-
ceptable allowances for manufacturing variations, are given.
This specification is under the jurisdiction of ASTM Committee E20 on
Temperature Measurement and is the direct responsibility of Subcommittee E20.04 4.3 A set of standard tests to be applied to all thermocouples
on Thermocouples.
covered by this specification are described together with a
Current edition approved May 10, 2000. Published August 2000. Originally
published as E 608–77. Last previous edition E 608–95.
Annual Book of ASTM Standards, Vol 03.03.
3 5
Discontinued. See 1999 Annual Book of ASTM Standards, Vol 03.03. Available from the American Welding Society, 2501 North West 7th St., Miami,
Annual Book of ASTM Standards, Vol 14.03. FL 33125.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 608/E 608M
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 12 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)
group of optional tests from which applicable additional 5.4 The type of sheath material. See Table 2 or Specification
requirements may be selected. E 585/E 585M.
4.4 Warning—Users should be aware that certain charac-
5.5 The type of measuring junction, Class 1 (grounded) or
teristics of thermocouples might change with time and use. If
Class 2 (ungrounded). See Figs. 1 and 2. If more than one pair
a thermocouple’s designed shipping, storage, installation, or
of thermoelements is specified, Class 2 is further subdivided
operating temperature has been exceeded, the thermocouple’s
into Class 2A (common ungrounded) and Class 2B (isolated
moisture seal may have been compromised and may no longer
ungrounded). Do not specify Class 1 grounded junctions with
adequately prevent the deleterious intrusion of water vapor.
Type T thermoelements (see 6.3.2).
Consequently, the thermocouple’s condition established by test
5.6 The quantity, length, and length tolerance of each
at time of manufacture may not apply later during an extended
thermocouple. See Figs. 3-6 for examples.
period of use, and retesting may become necessary. In addition,
inhomogeneities can develop in thermoelements because of
5.7 The type and configuration of connection head, connec-
exposure to temperature, even in cases where maximum
tor, transition piece, or termination, and moisture seal required
exposure temperatures have been lower than the suggested
on the end opposite the measuring junction. See Figs. 3-6 for
upper temperature limits of Table 1. For this reason, calibration
examples. The minimum and maximum intended operating
of thermocouples destined for delivery to a customer is not
temperature of the connection head, transition, or termination,
recommended (see S6.1). Because the emf indication of any
and moisture seal should be specified (6.6). For thermocouples
thermocouple depends upon the condition of the thermoele-
with insulated wire attached (Fig. 6) and Class 2 junctions,
ments along their entire length as well as the temperature
state the minimum acceptable insulation resistance (6.7).
profile pattern in the region of any inhomogeneity, the emf
5.8 Optional supplementary testing requirements and test
output of a used thermocouple will be unique to its installation.
sample rate (8.2).
Because temperature profiles in calibration equipment are
5.9 The Quality Assurance or Verification Program Require-
unlikely to duplicate those of the installation, removal of a used
ments, or both, including material traceability if required. See
thermocouple to a separate apparatus for calibration is not
recommended. Instead, in situ calibration by comparison to a
Appendix X1.
similar thermocouple known to be good is often recommended.
5.10 Any deviations from this specification or the refer-
enced specifications.
5. Ordering Information
5.11 Shipping method and straightness criteria, if required
5.1 The purchase documents shall specify the following
(see 10.2).
options:
5.12 The minimum and maximum intended operating tem-
5.1.1 The type and quantity of thermoelement pairs, and the
peratures of the thermocouple (see S6.1).
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 Al O ). See
2 3 “Manual on the Use of Thermocouples in Temperature Measurement,” ASTM
Specification E 585/E 585M. Manual 12, ASTM, 1993.
E 608/E 608M
TABLE 2 Weld Closure Filler Metal
electrical insulation specified in Table 4 shall also apply
AWS between thermoelement pairs. The minimum insulation value
Weld Rod AWS
Sheath Material Specifica-
shall be negotiated between the purchaser and the producer for
Type
tion
Fig. 6 assemblies with purchaser specified insulated thermo-
Austenitic Stainless Steels
couple extension wire or other devices attached. For Fig. 5
TP 304 ER 308 A5.9
assemblies, the minimum insulation resistance values of Table
TP 304L ER 308L A5.9
TP 310 ER 310 A5.9
4 shall be imposed before the thermocouple is terminated
TP 316 ER 316 A5.9
(when it is like Fig. 4). The insulation resistance shall be tested
TP 316L ER 316L A5.9
in accordance with Test Method E 780.
TP 317 ER 317 A5.9
TP 321 ER 347 A5.9
6.8 Sheath Condition—The surface of the completed ther-
TP 347 ER 347 A5.9
mocouples shall be visually clean, dry, and oxide-free.
TP 348 ER 348 A5.9
Nickel-chromium-iron alloy ER NiCrFe-5 A5.14
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-
6. General Requirements
ments, as desired by the purchaser.
6.1 Tagging—During fabrication, each thermocouple shall
6.10 All testing and inspection shall be performed in accor-
be tagged with a unique identification number to keep trace-
dance with Test Methods E 839 unless otherwise indicated.
ability to materials and test data. The producer’s standard
tagging method may be used.
7. Measuring Junction Configuration
6.2 Welding Rod—Filler material used for welding or plug-
ging the end closure shall comply with Table 2. 7.1 The measuring junction configurations are shown in
6.3 Measuring Junctions:
cross section in Figs. 1 and 2. The tip shape is optional as long
6.3.1 The end closure shall be impervious to gases and
as the dimensional requirements are maintained. The preferred
liquids. There shall be no cracks, holes, or void defects that
nominal sheath diameters are listed in Table 1 or Specification
penetrate through the metal wall. Any mineral oxide removed
E 585/E 585M. The measuring junction dimensional require-
during fabrication of the measuring junction shall be replaced
ments are as follows:
with dry oxide of the same type that conforms to the purity
7.1.1 Dimension A, End Closure Diameter, Classes 1 and
requirements of Specification E 585/E 585M. Class 2 measur-
2—The end closure maximum diameter shall be no larger than
ing junctions shall be fabricated by welding the thermoele-
the nominal sheath diameter plus a weld allowance of 0.05 mm
ments without filler metal or flux.
(0.002 in.) or 2 % of the nominal sheath diameter, whichever is
6.3.2 The measuring junction end closures shall be seal
larger. Localized reduction of the end closure diameter caused
welded. The use of plugs or filler metals is optional. Class 1
by weld shrinkage shall not exceed 0.05 mm (0.002 in.) or 2 %
(grounded) measuring junctions on Type T thermocouples are
of the nominal sheath diameter, whichever is larger. This
excluded from this specification because of the problems
expanded end closure diametral tolerance shall apply from the
associated with welding the copper thermoelement.
tip of the end closure over a length not exceeding 23 the
6.4 Standard Tolerances—Sheathed thermocouples fabri-
nominal sheath diameter.
cated to this specification shall conform to the standard
7.1.2 Dimensions Controlled by Supplementary Radio-
tolerances (see Table 3) in accordance with Specification
graphic Inspection (see Supplementary Requirement S1):
E 230, unless otherwise specified.
7.1.2.1 Dimension B, Measuring Junction Length—The
6.5 Special Tolerances—If specified in the purchase docu-
measuring junction length on Class 2A and Class 2B junctions
ment, the special tolerances (see Table 3) in accordance with
shall be a minimum of one and a maximum of four thermo-
Specification E 230, shall apply.
element diameters long.
6.6 Termination—The sheathed thermocouples shall be ter-
7.1.2.2 Dimension C, Minimum Measuring Junction Insula-
minated at the end opposite the measuring junction in a manner
tion Thickness, Radial Dimension—The minimum insulation
specified by the purchaser. All exposed MgO or Al O shall be
2 3
thickness on Class 2A and 2B junctions, as measured from the
sealed from moisture to keep the insulation dry. All connectors,
junction to the sheath in a radial direction, shall be 5 % of the
connection heads, or transitions shall include a positive method
nominal sheath diameter.
of preventing strain on the thermoelements emerging from the
7.1.2.3 Dimension D, Minimum Material Thickness, Class 1
sheathed material. All transitional wire connections shall be
and Class 2 Junctions—The thickness at any point of the end
brazed or welded. The moisture seal and termination (see Figs.
closur
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