# ASTM C335C335M-17

Designation: C335/C335M − 17Standard Test Method forSteady-State Heat Transfer Properties of Pipe Insulation1This standard is issued under the fixed designation C335/C335M; the number immediately following the designation indicates the yearof 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 (´) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers the measurement of the steady-state heat transfer properties of pipe insulations. Specimentypes include rigid, flexible, and loose fill; homogeneous andnonhomogeneous; isotropic and nonisotropic; circular or non-circular cross section. Measurement of metallic reflectiveinsulation and mass insulations with metal jackets or otherelements of high axial conductance is included; however,additional precautions must be taken and specified specialprocedures must be followed.1.2 The test apparatus for this purpose is a guarded-end orcalibrated-end pipe apparatus. The guarded-end apparatus is aprimary (or absolute) method. The guarded-end method iscomparable, but not identical to ISO 8497.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4 When appropriate, or as required by specifications orother test methods, the following thermal transfer propertiesfor the specimen can be calculated from the measured data (see3.2):1.4.1 The pipe insulation lineal thermal resistance andconductance,1.4.2 The pipe insulation lineal thermal transference,1.4.3 The surface areal resistance and heat transfercoefficient,1.4.4 The thermal resistivity and conductivity,1.4.5 The areal thermal resistance and conductance, and1.4.6 The areal thermal transference.NOTE 1—In this test method the preferred resistance, conductance, andtransference are the lineal values computed for a unit length of pipe. Thesemust not be confused with the corresponding areal properties computed ona unit area basis which are more applicable to flat slab geometry. If theseareal properties are computed, the area used in their computation must bereported.NOTE 2—Discussions of the appropriateness of these properties toparticular specimens or materials may be found in Test Method C177, TestMethod C518, and in the literature (1).21.5 This test method allows for operation over a wide rangeof temperatures. The upper and lower limit of the pipe surfacetemperature is determined by the maximum and minimumservice temperature of the specimen or of the materials used inconstructing the apparatus. In any case, the apparatus must beoperated such that the temperature difference between theexposed surface and the ambient is sufficiently large enough toprovide the precision of measurement desired. Normally theapparatus is operated in closely controlled still air ambientfrom 15 to 30°C, but other temperatures, other gases, and othervelocities are acceptable. It is also acceptable to control theouter specimen surface temperature by the use of a heated orcooled outer sheath or blanket or by the use of an additionaluniform layer of insulation.1.6 The use any size or shape of test pipe is allowableprovided that it matches the specimens to be tested. Normallythe test method is used with circular pipes; however, its use ispermitted with pipes or ducts of noncircular cross section(square, rectangular, hexagonal, etc.). One common size usedfor interlaboratory comparison is a pipe with a circular crosssection of 88.9-mm diameter (standard nominal 80-mm [3-in.]pipe size), although several other sizes are reported in theliterature (2-4).1.7 The test method applies only to test pipes with ahorizontal or vertical axis. For the horizontal axis, the literatureincludes using the guarded-end, the calibrated, and thecalibrated-end cap methods. For the vertical axis, no experi-ence has been found to support the use of the calibrated orcalibrated-end methods. Therefore the method is restricted tousing the guarded-end pipe apparatus for vertical axis mea-surements.1.8 This test method covers two distinctly different types ofpipe apparatus, the guarded-end and the calibrated or1This test method is under the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.30 on ThermalMeasurement.Current edition approved May 1, 2017. Published October 2017. Originallyapproved in 1954. Last previous edition approved in 2010 as C335/C335M – 10ε1.DOI: 10.1520/C0335_C0335M-17.2The boldface numbers in parentheses refer to the references at the end of thistest method.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1calculated-end types, which differ in the treatment of axial heattransfer at the end of the test section.1.8.1 The guarded-end apparatus utilizes separately heatedguard sections at each end, which are controlled at the sametemperature as the test section to limit axial heat transfer. Thistype of apparatus is preferred for all types of specimens withinthe scope of this test method and must be used for specimensincorporating elements of high axial conductance.1.8.2 The calibrated or calculated-end apparatus utilizesinsulated end caps at each end of the test section to minimizeaxial heat transfer. Corrections based either on the calibrationof the end caps under the conditions of test or on calculationsusing known material properties, are applied to the measuredtest section heat transfer. These apparatuses are not applicablefor tests on specimens with elements of high axial conductancesuch as reflective insulations or metallic jackets. There is noknown experience on using these apparatuses for measure-ments using a vertical axis.1.9 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, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.10 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3C168 Terminology Relating to Thermal InsulationC177 Test Method for Steady-State Heat Flux Measure-ments and Thermal Transmission Properties by Means ofthe Guarded-Hot-Plate ApparatusC302 Test Method for Density and Dimensions of Pre-formed Pipe-Covering-Type Thermal InsulationC518 Test Method for Steady-State Thermal TransmissionProperties by Means of the Heat Flow Meter ApparatusC680 Practice for Estimate of the Heat Gain or Loss and theSurface Temperatures of Insulated Flat, Cylindrical, andSpherical Systems by Use of Computer ProgramsC870 Practice for Conditioning of Thermal Insulating Ma-terialsC1045 Practice for Calculating Thermal Transmission Prop-erties Under Steady-State ConditionsC1058 Practice for Selecting Temperatures for Evaluatingand Reporting Thermal Properties of Thermal InsulationE230 Specification and Temperature-Electromotive Force(EMF) Tables for Standardized Thermocouples2.2 ISO Standards:ISO 8497 Thermal Insulation-Dermination of Steady StateThermal Transmission Properties of Thermal Insulationfor Circular Pipes3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at service@astm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.TABLE 1 Conversion Factors (International Table)NOTE 1—For thermal conductance per unit length or thermal transference per unit length, use the inverse of the table for thermal resistance per unitlength. For thermal resistivity, use the inverse of the table for thermal conductivity. For thermal conductance (per unit area) or thermal transference (perunit area), use the inverse of the table for thermal resistance (per unit area).Thermal Resistance per Unit LengthAK·m·W−1(B)K·cm·W−1K·cm·s·cal−1K·m·h·kg-cal−1°F·ft·h·Btu−11 K·m·W−1= 1.000 100.0 418.7 1.163 1.7311 K·cm·W−1= 1.000×10−21.000 4.187 1.163 × 10−21.731 × 10−21 K·cm·s·cal−1= 2.388×10−30.2388 1.000 2.778 × 10−34.134 × 10−31 K·m·h·kg-cal−1= 0.8598 85.98 360.0 1.000 1.4881°F·ft·h·Btu−1= 0.5778 57.78 241.9 0.6720 1.000Thermal ConductivityAW·m−1·K−1(B)W·cm−1·K−1cal·s−1·cm−1·K−1kg-cal·h−1·m−1·K−1Btu·h−1·ft−1·°F−1Btu·in.·h−1·ft−2°F−11W·m−1·K−1= 1.000 1.000 × 10−22.388 × 10−30.8598 0.5778 6.9331 W·cm−1·K−1= 100.0 1.000 0.2388 85.98 57.78 693.31 cal·s−1·cm−1·K−1= 418.7 4.187 1.000 360.0 241.9 2903.1 kg-cal·h−1·m−1·K−1= 1.163 1.163 × 10−22.778 × 10−31.000 0.6720 8.0641 Btu·h−1·ft−1·°F−1= 1.731 1.731 × 10−24.134 × 10−31.488 1.000 12.001 Btu·in.·h−1·ft−2·°F−1= 0.1442 1.442 × 10−33.445 × 10−40.1240 8.333 × 10−21.000Thermal Resistance per Unit AreaAK·m2·W−1( B)K·cm2·W−1K·cm2·s·cal−1K·m2·h·kg-cal−1°F·ft2·h·Btu−11K·m2·W−1= 1.000 1.000 × 1044.187 × 1041.163 5.6781 K·cm2·W−1= 1.000×10−41.000 4.187 1.163 × 10−45.678 × 10−41 K·cm2·s·cal−1= 2.388×10−50.2388 1.000 2.778 × 10−51.356 × 10−41K·m2·h·kg-cal−1= 0.8598 8.594 × 1033.600 × 1041.000 4.8821°F·ft2·h·Btu−1= 0.1761 1.761 × 1037.373 × 1030.2048 1.000AUnits are given in terms of (1) the absolute joule per second or watt, (2) the calorie (International Table) = 4.1868 J, or the British thermal unit (InternationalTable) = 1055.06 J.BThis is the SI (International System of Units) unit.C335/C335M − 1722.3 ASTM Adjuncts:4Guarded-end ApparatusCalibrated-end Apparatus3. Terminology3.1 Definitions—For definitions of terms used in this testmethod, refer to Terminology C168.3.2 Definitions of Terms Specific to This Standard:3.2.1 areal thermal conductance, C—the steady-state timerate of heat flow per unit area of a specified surface (Note 3)divided by the difference between the average pipe surfacetemperature and the average insulation outer surface tempera-ture. It is the reciprocal of the areal thermal resistance, R.C 5QA~to2 t2!51R(1)where the surface of the area, A, must be specified (usu-ally the pipe surface or sometimes the insulation outer sur-face).NOTE 3—The value of C, the areal thermal conductance, is arbitrarysince it depends upon an arbitrary choice of the area, A. For a homoge-neous material for which the thermal conductivity is defined as in 3.2.7(Eq 8), the areal conductance, C, is given as follows:C 52πLλpAln~r2/ro!(2)If the area is specially chosen to be the “log mean area,”equal to 2πL (r2− ro)/l n(r2/ro), then C = λp/(r2− ro). Since(r2− ro) is equal to the insulation thickness measured fromthe pipe surface, this is analogous to the relation betweenconductance and conductivity for flat slab geometry. Similarrelations exist for the areal thermal resistance defined in3.2.2. Since these areal coefficients are arbitrary, and sincethe area used is often not stated, thus leading to possibleconfusion, it is recommended that these areal coefficients notbe used unless specifically requested.3.2.2 areal thermal resistance, R—the average temperaturedifference between the pipe surface and the insulation outersurface required to produce a steady-state unit rate of heat flowper unit area of a specified surface (Note 3). It is the reciprocalof the areal thermal conductance, C.R 5A~to2 t2!Q51C(3)where the surface of the area, A, must be specified (usu-ally the pipe surface or sometimes the insulation outer sur-face).3.2.3 areal thermal transference, Tr—the time rate of heatflow per unit surface area of the insulation divided by thedifference between the average pipe surface temperature andthe average air ambient temperature.Tr5Q2πr2L~to2 ta!(4)3.2.4 pipe insulation lineal thermal conductance, CL—thesteady-state time rate of heat flow per unit pipe insulationlength divided by the difference between the average pipesurface temperature and the average insulation outer surfacetemperature. It is the reciprocal of the pipe insulation linealthermal resistance, RL.CL5QL~to2 t2!51RL(5)3.2.5 pipe insulation lineal thermal resistance, RL—theaverage temperature difference between the pipe surface andthe insulation outer surface required to produce a steady-stateunit time rate of heat flow per unit of pipe insulation length. Itis the reciprocal of the pipe insulation lineal thermalconductance, CL.RL5L~to2 t2!Q51CL(6)3.2.6 pipe insulation lineal thermal transference, Trp—thesteady-state time rate of heat flow per unit pipe insulationlength divided by the difference between the average pipesurface temperature and the average air ambient temperature. Itis a measure of the heat transferred through the insulation to theambient environment.Trp5QL~to2 ta!(7)3.2.7 pipe insulation thermal conductivity,λp—of homoge-neous material, the ratio of the steady-state time rate of heatflow per unit area to the average temperature gradient (tem-perature difference per unit distance of heat flow path). Itincludes the effect of the fit upon the test pipe and is thereciprocal of the pipe insulation thermal resistivity, rL. For pipeinsulation of circular cross section, the pipe insulation thermalconductivity is:λp5Q 1n~r2/ro!L2π~to2 t2!51rL(8)3.2.8 pipe insulation thermal resistivity, rL—of homoge-neous material, the ratio of the average temperature gradient(temperature difference per unit distance of heat flow path) tothe steady-state time rate of heat flow per unit area. It includesthe effect of the fit upon the test pipe and is the reciprocal of thepipe insulation thermal conductivity, λp. For pipe insulation ofcircular cross section, the pipe insulation thermal resistivity iscalculated as follows:rL52πL~to2 t2!Q 1n ~r2/ro!51λp(9)3.2.9 surface areal heat transfer coeffıcient, h2—the ratio ofthe steady-state time rate of heat flow per unit surface area tothe average temperature difference between the surface and theambient surroundings. The inverse of the surface heat transfercoefficient is the surface resistance. For circular cross sections:h25Q2πr2L~t22 ta!(10)3.3 Symbols: see 1.3:CL= pipe insulation lineal thermal conductance, W/m·K[Btu·in⁄F·hr·ft2],4Documents showing details of both guarded-end and calibrated-end apparatuscomplying with the requirements o