1、Designation: E 633 00 (Reapproved 2005)Standard Guide forUse of Thermocouples in Creep and Stress-Rupture Testingto 1800F (1000C) in Air1This standard is issued under the fixed designation E 633; the number immediately following the designation indicates the year oforiginal adoption or, in the case
2、of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis guide provides basic information, options, and guidelines to enable the user to applyth
3、ermocouples, temperature measurement, and control equipment with sufficient accuracy to satisfythe temperature requirements for creep and stress-rupture testing of materials.1. Scope1.1 This guide covers the use of ANSI thermocouple TypesK, N, R, and S for creep and stress-rupture testing at tempera
4、-tures up to 1800F (1000C) in air at one atmosphere ofpressure. It does not cover the use of sheathed thermocouples.1.2 The values stated in inch-pound units are to be regardedas the standard. The values given in parentheses are forinformation only.1.3 This standard does not purport to address all o
5、f thesafety concerns, if any, associated with its use. It is theresponsibility 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 Documents2.1 ASTM Standards:2E 139 Practice for Cond
6、ucting Creep, Creep-Rupture, andStress-Rupture Tests of Metallic MaterialsE 207 Test Method of Thermal EMF Test of Single Ther-moelement Materials by Comparison with a SecondaryStandard of Similar EMF-Temperature PropertiesE 220 Test Method for Calibration of Thermocouples byComparison TechniquesE 2
7、30 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE 292 Test Methods for Conducting Time-For-RuptureNotch Tension Tests of MaterialsE 344 Terminology Relating to Thermometry and Hydrom-etryE 574 Specification for Duplex Base Metal ThermocoupleWire with Gl
8、ass Fiber or Silica Fiber InsulationE 1129/E 1129M Specification for Thermocouple Connec-torsE 1684 Specification for Miniature Thermocouple Connec-tors3. Terminology3.1 DefinitionsUnless otherwise indicated, the definitionsgiven in Terminology E 344 shall apply.4. Classification4.1 The following th
9、ermocouple types are identified inTables E 230:4.1.1 Type KNickel10 % chromium ( + ) versusnickel5 % (aluminum, silicon) (),4.1.2 Type NNickel14 % chromium, 1.5 % silicon ( + )versus nickel4.5 % silicon0.1 % magnesium (),4.1.3 Type RPlatinum13 % rhodium ( + ) versus plati-num (),4.1.4 Type SPlatinum
10、10 % rhodium ( + ) versus plati-num ().5. Summary of Guide5.1 This guide will help the user to conduct a creep orstress-rupture test with the highest degree of temperatureprecision available. It provides information on the proper1This guide is under the jurisdiction of ASTM Committee E20 on Temperat
11、ureMeasurement and is the direct responsibility of Subcommittee E20.04 on Thermo-couples.Current edition approved May 1, 2005. Published May 2005. Originallyapproved in 1987. Last previous edition approved in 2000 as E 63300.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcon
12、tact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.application of thermo
13、couples that are used to measure andcontrol the temperature of the test specimen. It also points outsources of error and suggests methods to eliminate them.6. Significance and Use6.1 This guide presents techniques on the use of thermo-couples and associated equipment for measuring temperaturein cree
14、p and stress-rupture testing in air at temperatures up to1800F (1000C).6.2 Since creep and stress-rupture properties are highlysensitive to temperature, users should make every effortpracticable to make accurate temperature measurements andprovide stable control of the test temperature. The goal of
15、thisguide is to provide users with good pyrometric practice andtechniques for precise temperature control for creep andstress-rupture testing.6.3 Techniques are given in this guide for maintaining astable temperature throughout the period of test.6.4 If the techniques of this guide are followed, the
16、 differ-ence between “indicated”3temperature and “true”4tempera-ture will be reduced to the lowest practical level.7. Apparatus7.1 Instrumentation may be individual instruments, a dataacquisition system (multipoint recorders or digital type), acomputer-based control system, or a combination of these
17、devices. (WarningSince each thermocouple is “grounded”by contacting the specimen, it is necessary that the instrumen-tation treat each thermocouple as isolated or “floating” from allother thermocouples. Neither leg should be connected to acommon ground at the instrumentation end of the system.Also,e
18、quipment having a high common mode rejection ratio isnecessary because of the proximity of strong electromagneticfields from the heating elements of the furnace.)7.2 Temperature Measurement InstrumentationThe mea-surement system should be able to resolve the thermocouplesignal to 60.1F (0.05C). The
19、temperature indication shouldhave no more than 61.0F (0.5C) uncertainty for the purposesof this test. In addition, where specific corrections for thecalibration of individual thermocouples or a thermocouple lotis required, the capability of the instrumentation system toaccommodate these data shall b
20、e considered.7.2.1 Reference Junction Compensation:7.2.1.1 Thermocouples are usually calibrated to a 32F(0C) reference temperature. Unless an ice point reference isused, some means must be provided to compensate for thetemperature where the thermoelectric circuit connects to theinstrument (refer to
21、MNL-12 on Reference Junctions5).7.2.1.2 Reference junction compensation is usually per-formed within the instrumentation itself. Most devices orelectronic data acquisition systems measure the temperaturewhere the thermoelements connect to the input terminals andintroduce a compensating emf to simula
22、te the ice point.7.2.1.3 The input connections shall be isothermal andshielded from sudden changes of temperature.7.2.2 RecalibrationThe accuracy of the temperature mea-surement equipment may be affected by component aging,environment, handling, or wear. Therefore, a periodic recali-bration of the m
23、easuring instrumentation with a checkinginstrument is necessary. The checking instrument should be ofhigher accuracy than the measurement system, and to ensureconformity to national standards, it should be calibrated with aknown primary test standard, traceable to the National Instituteof Standards
24、and Technology.7.3 Temperature Control Equipment RequirementsA tem-perature controller or temperature control system should beselected on the basis of stability (variations of 61F (0.5C) orless), and accuracy (uncertainty of 61.5F (0.7C) or less).Generally, a control system with proportional band, a
25、utomaticreset, and slow approach to final set point features should beused. When employing an automatic feedback control system,the tuning constants or control algorithm shall be optimized,not only to maintain the test specimen at the set point withoutexcessive deviations, but to eliminate or limit
26、the amount ofovershoot upon initial heating.NOTE 1The same precautions regarding reference junction compen-sation in the control device apply as in 7.2.1.7.3.1 ConfigurationThe control configuration may takeone of several forms:7.3.1.1 The center thermocouple is connected to a controlloop that striv
27、es to maintain the temperature of the center of thereduced section at set point. The upper and lower thermo-couples are used to measure the temperatures at the ends of thereduced section. Means shall be provided to adjust the heatingpower above and below the center to equalize the temperatures.7.3.1
28、.2 The bottom and top thermocouples may be con-nected to control loops that regulate the power to the upper andlower heaters independently. Thus, the end temperatures aremaintained automatically. The center thermocouple is usedonly as a monitor.7.3.2 Control System Recalibration and ReliabilityTheco
29、ntrol system should be subjected to routine recalibration, ascircumstances and type of equipment dictate. The checkingprocedure should include calibration of the controller and asensitivity check. A calibration circuit, as shown in AppendixX1, should be employed.7.4 Heating EquipmentFurnaces should
30、be appropriatelysized or adjusted relative to the workload and heat losses toprovide a zone of uniform temperature across the specimen.Because creep and stress-rupture testing is usually done atconstant temperature and with an unchanging furnace load, themain requirement is a well-insulated furnace,
31、 capable ofachieving the desired temperatures. The top and bottom open-ings should be closed to limit convection losses, but thefurnace should not be sealed airtight.8. Hazards8.1 The duration of a creep test ranges from a few hours toseveral hundred hours at elevated temperatures, at least par-tial
32、ly unattended by operators. Such tests are normally endedbefore test specimen failure. Stress-rupture tests may operate at3As defined in Practice E 139 and Test Methods E 292.4As defined in Practice E 139.5Manual on the Use of Thermocouples in Temperature Measurement, ASTMMNL-12.E 633 00 (2005)2high
33、er stresses, higher temperatures, and for shorter times thancreep tests, but they normally continue until the specimen hasachieved its required life or has failed.8.2 The stability of the emf of the thermocouples and therapid response of the control system to any changes oftemperature over the perio
34、d of the test are crucial to maintainthe specimen within the allowable temperature band.8.3 Thermocouple RequirementsThe requirements forthermocouples used for measurement are somewhat differentfrom thermocouples used for control purposes (especially withautomatic feedback control systems). Of cours
35、e, both require-ments may be met with one set of thermocouples that isjudiciously chosen and placed.8.3.1 MeasurementThermocouples used for measurementare designed to represent the temperature of the specimenalong its reduced section.4Since only two or three thermo-couples are used, they shall be lo
36、cated at places on thespecimen that represent the average temperature of theirrespective sections. This can be determined by a test program,where more than the usual number of thermocouples aremounted along the reduced section to establish the temperatureprofile.8.3.2 ControlThermocouples used for c
37、ontrol are de-signed and placed to be sensitive to changes of or impendingchanges to the temperature of the specimen. Control thermo-couple wire should be as thin as possible. However, the wireshould not be so thin that oxidation or strain would cause emferrors or failure during the test period.NOTE
38、 2Locating a control thermocouple next to the heater as a meansto limit fluctuations of temperature is not advisable. A controller with awide proportional band and automatic reset is capable of compensating forthe thermal lag of most furnace designs.9. Thermocouples9.1 Basic InformationInformation o
39、n basic thermocouplecharacteristics and performance is available from ASTM pub-lications such as MNL-12.5Stability of the emf over the periodof test is the most crucial requirement for a control thermo-couple, whereas accuracy of the measurement thermocouple isparamount for successful correlation of
40、 test results.9.1.1 Factors affecting thermocouple selection are: atmo-sphere, temperature of exposure, duration of testing, andresponse time. These factors should be considered to determinetype (K, N, R, or S), wire size, insulation, and installationmethods.9.2 PrecautionsThe emf output of a thermo
41、couple isaffected by inhomogeneities in the region of a temperaturegradient. Inhomogeneities are produced by cold work, con-tamination, or metallurgical changes produced by temperatureitself. Therefore, thermocouples should be handled carefullywithout unnecessary stretching, bending, or twisting the
42、 wires.Bending around small radii should be avoided entirely, espe-cially where the wires may lie in a temperature gradient.Wherenecessary, a minimum amount of bending may be performedcarefully around bend radii at least 20 times the diameter of thewire.9.3 Types K and N Thermocouples:9.3.1 Suitabil
43、ityTypes K and N thermocouples are usefulfor creep and rupture testing because they provide a relativelyhigh emf and are relatively stable over the low and middletemperatures of the testing range.9.3.2 LimitationsConventional Type K, and to a lesserextent, Type N thermocouples undergo emf drift as t
44、he result ofmetallurgical changes during use. Therefore, that portion ofwire that has been exposed to temperatures above 500F(260C) or 1600F (870C) for Types K and N thermocouples,respectively, should be discarded after one use.9.3.3 AssessmentType K or N thermocouples should bereused only after the
45、ir suitability for a particular test programis proven by a body of test data. Stability tests are advised,using Type R or S thermocouples as references.9.4 Types R and S Thermocouples:9.4.1 SuitabilityTypes R and S are highly resistant tooxidation and are therefore stable for these tests at the high
46、ertemperatures of the range. They provide the highest reproduc-ibility and repeatability of the several thermocouple types butare initially more costly. Because they do not deteriorate duringnormal use, it is possible to reuse them. When Types R and Swires are no longer suitable for service, they st
47、ill retain asignificant portion of their initial cost in salvage value.9.4.2 LimitationsThe limiting factor for reuse of Type Ror S thermocouples is error introduced by strain or contami-nation. Wires of Types R and S are mechanically weaker thanTypes K and N, so they must be adequately supported to
48、 avoidstraining them. Sufficient slack should be provided so that thewires do not strain or tear when the specimen elongates.TABLE 1 Thermocouple and Extension Wire Tolerances andCalibration UncertaintiesThermocouples, FTypeTemperatureRangeToleranceTypicalCalibrationUncertaintyAStandardBSpecialK, N
49、32 to 2000 4 or 0.75 % 2 or 0.4 % 1.8 to 2.2S, R 32 to 2000 2.7 or 0.25 % 1 or 0.1 % 1.1 to 1.2Extension Wire, FCKX, NX 32 to 400 4D0.5to2RX, SX 32 to 400 9D2to4Thermocouples, CTypeTemperatureRangeToleranceTypicalCalibrationUncertaintyAStandardBSpecialK, N 0 to 1100 2.2 or 0.75 % 1.1 or 0.4 % 1 to 1.2R, S 0 to 1100 1.5 or 0.25 % 0.6 or 0.1 % 0.6 to 0.7Extension Wire, CCKX, NX 0 to + 200 2D0.3to1RX, SX 0 to + 200 5D1to2ACalibration uncertainty in an actual test depends on number of test points,media, and reference standard used
