1、Designation: E633 13Standard Guide forUse of Thermocouples in Creep and Stress-Rupture Testingto 1800F (1000C) in Air1This standard is issued under the fixed designation E633; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONThis guide provides basic information, options, and guidelines to enable the user to applythermocouples, temperat
3、ure measurement, and control equipment with sufficient accuracy to satisfythe temperature requirements for creep and stress-rupture testing of materials.1. Scope*1.1 This guide covers the use of ANSI thermocouple TypesK, N, R, and S for creep and stress-rupture testing at tempera-tures up to 1800F (
4、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 standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considere
5、d standard.1.3 This standard does not purport to address all of 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. R
6、eferenced Documents2.1 ASTM Standards:2E6 Terminology Relating to Methods of Mechanical TestingE21 Test Methods for ElevatedTemperatureTensionTests ofMetallic MaterialsE139 Test Methods for Conducting Creep, Creep-Rupture,and Stress-Rupture Tests of Metallic MaterialsE207 Test Method for Thermal EMF
7、 Test of Single Thermo-element Materials by Comparison with a Reference Ther-moelement of Similar EMF-Temperature PropertiesE220 Test Method for Calibration of Thermocouples ByComparison TechniquesE230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized ThermocouplesE292 T
8、est Methods for Conducting Time-for-Rupture NotchTension Tests of MaterialsE344 Terminology Relating to Thermometry and Hydrom-etryE574 Specification for Duplex, Base Metal ThermocoupleWire With Glass Fiber or Silica Fiber InsulationE1129/E1129M Specification for Thermocouple ConnectorsE1684 Specifi
9、cation for Miniature Thermocouple Connec-tors3. Terminology3.1 DefinitionsUnless otherwise indicated, the definitionsgiven in Terminology E6 and E344 shall apply.4. Classification4.1 The following thermocouple types are identified inTables E230:4.1.1 Type KNickel10 % chromium ( + ) versusnickel5 % (
10、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 SPlatinum10 % rhodium ( + ) versus plati-num ().5. Summary of Guide5.1 This guide will help the user to conduct
11、 a creep orstress-rupture test with the highest degree of temperatureprecision available. It provides information on the properapplication of thermocouples that are used to measure andcontrol the temperature of the test specimen. It also points outsources of error and suggests methods to eliminate t
12、hem.1This guide is under the jurisdiction of ASTM Committee E28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.04 on Uniaxial Testing.Current edition approved Nov. 1, 2013. Published December 2013. Originallyapproved in 1987. Last previous edition approved in 2005 as E6330
13、0(2005). DOI:10.1520/E0633-13.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.*A Summary of Changes section a
14、ppears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. Significance and Use6.1 This guide presents techniques on the use of thermo-couples and associated equipment for measuring temperaturein creep and st
15、ress-rupture testing in air at temperatures up to1800F (1000C). The duration of a creep test ranges from afew hours to several thousand hours or more at elevatedtemperatures, at least partially unattended by operators. Suchtests are normally ended before test specimen failure. Stress-rupture tests m
16、ay operate at higher stresses, highertemperatures, and for shorter times than creep tests, but theynormally continue until the specimen has achieved its requiredlife or has failed.6.2 Since creep and stress-rupture properties are highlysensitive to temperature, users should make every effortpractica
17、ble to make accurate temperature measurements andprovide stable control of the test temperature. The goal of 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 mainta
18、ining astable temperature throughout the period of test.6.4 If the techniques of this guide are followed, the differ-ence between indicated temperature and true temperature, asused in E139, E292, and E21 will be reduced to the lowestpractical level.7. Apparatus7.1 Instrumentation may be individual i
19、nstruments, a dataacquisition system (multipoint recorders or digital type), acomputer-based control system, or a combination of thesedevices.NOTE 1Since each thermocouple is “grounded” by contacting thespecimen, it is necessary that the instrumentation treat each thermocoupleas isolated or “floatin
20、g” from all other thermocouples. Neither leg shouldbe connected to a common ground at the instrumentation end of thesystem. Also, equipment having a high common mode rejection ratio isnecessary because of the proximity of strong electromagnetic fields fromthe heating elements of the furnace.7.2 Temp
21、erature Measurement InstrumentationThe mea-surement system should be able to resolve the thermocouplesignal to 60.1F (0.05C). The temperature indication shouldhave no more than 61.0F (0.5C) uncertainty for the purposesof this test. In addition, where specific corrections for thecalibration of indivi
22、dual thermocouples or a thermocouple lotare required, the capability of the instrumentation system toaccommodate these data shall be 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,
23、 provide some means to compensate for the temperaturewhere the thermoelectric circuit connects to the instrument;refer to MNL-12 on Reference Junctions.37.2.1.2 Reference junction compensation is usually per-formed within the instrumentation itself. Most devices orelectronic data acquisition systems
24、 measure the temperaturewhere the thermoelements connect to the input terminals andintroduce a compensating emf to simulate 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 e
25、quipment may be affected by component aging,environment, handling, or wear. Therefore, a periodic recali-bration of the measuring instrumentation with a checkinginstrument is necessary. The checking instrument should be ofhigher accuracy than the measurement system, and to ensureconformity to nation
26、al standards, it should be calibrated with aknown primary test standard, traceable to a national metrologyinstitute.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
27、 accuracy (uncertainty of 61.5F (0.7C) or less).Generally, a control system with proportional band, automaticreset, 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 t
28、o maintain the test specimen at the set point withoutexcessive deviations, but to eliminate or limit the amount ofovershoot upon initial heating.NOTE 2The same precautions regarding reference junction compen-sation in the control device apply as in 7.2.1.7.3.1 ConfigurationThe control configuration
29、may takeone of two forms:7.3.1.1 The center thermocouple is connected to a controlloop that strives 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
30、provided to adjust the heatingpower above and below the center to equalize the temperatures.7.3.1.2 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 cen
31、ter thermocouple is usedonly as a monitor.7.3.2 Control System Recalibration and ReliabilityThecontrol 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 cali
32、bration circuit, as shown in AppendixX1, should be employed.7.4 Heating EquipmentFurnaces should 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
33、temperature and with an unchanging furnace load, themain requirement is a well-insulated furnace, 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.3Manual on the Use of Thermocouples i
34、n Temperature Measurement, FourthEdition, 1993. Sponsored by ASTM International Committee E20 on TemperatureMeasurement. ASTM International MNL-124th. DOI: 10.1520/MNL124TH-EB.E633 1328. Thermocouples8.1 The stability of the emf of the thermocouples and therapid response of the control system to any
35、 changes oftemperature over the period of the test are crucial to maintainthe specimen within the allowable temperature band.8.2 Thermocouple RequirementsThe requirements forthermocouples used for measurement are somewhat differentfrom thermocouples used for control purposes (especially withautomati
36、c feedback control systems). Of course, both require-ments may be met with one set of thermocouples that isjudiciously chosen and placed.8.2.1 MeasurementThermocouples used for measurementare designed to represent the temperature of the specimenalong its reduced section. Since only two or three ther
37、mo-couples are used, they shall be located 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.
38、8.2.2 ControlThermocouples used for control 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 small in diameter as possible.However, the wire should not be so small in diameter thatoxidation or strai
39、n would cause emf errors or failure during thetest period.NOTE 3Locating 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 furn
40、ace designs.8.3 Basic InformationInformation on basic thermocouplecharacteristics and performance is available from ASTM pub-lications such as MNL-12.3Stability of the emf over the periodof test is the most crucial requirement for a controlthermocouple, whereas accuracy of the measurement thermo-cou
41、ple is paramount for successful correlation of test results.8.3.1 Factors affecting thermocouple selection are:atmosphere, temperature of exposure, duration of testing, andresponse time. These factors should be considered to determinetype (K, N, R, or S), wire size, insulation, and installationmetho
42、ds.8.4 PrecautionsThe emf output of a thermocouple isaffected by inhomogeneities in the region of a temperaturegradient. Inhomogeneities are produced by cold work,contamination, or metallurgical changes produced by tempera-ture itself. Therefore, thermocouples should be handled care-fully without un
43、necessary stretching, bending, or twisting thewires. Bending around small radii should be avoided entirely,especially where the wires may lie in a temperature gradient.Where necessary, a minimum amount of bending may beperformed carefully around bend radii at least 20 times thediameter of the wire.8
44、.5 Types K and N Thermocouples:8.5.1 SuitabilityTypes 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.8.5.2 LimitationsConventional Type K, and to a lesserextent
45、, Type N thermocouples undergo emf drift as the 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.8.5.3 AssessmentType K or N
46、 thermocouples should bereused only after their 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.8.6 Types R and S Thermocouples:8.6.1 SuitabilityTypes R and S are highly resistant tooxidation and are
47、 therefore stable for these tests at the highertemperatures 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 Swire
48、s are no longer suitable for service, they still retain asignificant portion of their initial cost in salvage value.8.6.2 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 a
49、nd N, so they must be adequately supported to avoidstraining them. Sufficient slack should be provided so that thewires do not strain or tear when the specimen elongates.Contamination of the wire4may be caused by oils, grease, orother chemicals, and from metallic vapors from the testspecimen during heating.8.6.3 AssessmentA Type R or S thermocouple should notbe used indefinitely. One way to determine the end of its usefullife is to place a new thermocouple from the same lot beside theold one and compare outputs. Replace the ol
