ASTM_C_740_-_C_740M_-_13.pdf

Designation:C740/C740M13Standard Guide forEvacuated Reflective Insulation In Cryogenic Service1This standard is issued under the fixed designation C740/C740M;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.1.Scope1.1 This guide covers the use of thermal insulations formedby a number of thermal radiation shields positioned perpen-dicular to the direction of heat flow.These radiation shieldsconsist of alternate layers of a low-emittance metal and aninsulating layer combined such that metal-to-metal contact inthe heat flow direction is avoided and direct heat conduction isminimized.These are commonly referred to as multilayerinsulations(MLI)or super insulations(SI)by the industry.Thetechnology of evacuated reflective insulation in cryogenicservice,or MLI,first came about in the 1950s and 1960sprimarily driven by the need to liquefy,store,and transportlarge quantities of liquid hydrogen and liquid helium.(1-6)21.2 The practice guide covers the use of these MLI systemswhere the warm boundary temperatures are below approxi-mately 400 K.Cold boundary temperatures typically rangefrom 4 K to 100 K,but any temperature below ambient isapplicable.1.3 Insulation systems of this construction are used whenheat flux values well below 10 W/m2are needed for anevacuated design.Heat flux values approaching 0.1 W/m2arealso achievable.For comparison among different systems,aswell as for space and weight considerations,the effectivethermal conductivity of the system can be calculated for aspecific total thickness.Effective thermal conductivities of lessthan 1 mW/m-K 0.007 Btuin/hft2F or R-value 143 aretypical and values on the order of 0.01 mW/m-K have beenachieved 0.00007 Btuin/hft2F or R-value 14 300.(7)Thermal performance can also be described in terms of theeffective emittance of the system,or e.1.4 These systems are typically used in a high vacuumenvironment(evacuated),but soft vacuum or no vacuumenvironments are also applicable.(8)A welded metal vacuum-jacketed(VJ)enclosure is often used to provide the vacuumenvironment.1.5 The range of residual gas pressures is from 10-6torr to10+3torr(from 1.33-4Pa to 133 kPa)with or without differentpurge gases as required.Corresponding to the applications incryogenic systems,three sub-ranges of vacuum are also de-fined:from 10-6torr to 10-3torr(from 1.333-4Pa to 0.133Pa)high vacuum/free molecular regime,from 10-2torr to 10torr(from 1.33 Pa to 1333 Pa)soft vacuum,transition regime,from 100 torr to 1000 torr(from 13.3 kPato 133 kPa)novacuum,continuum regime.(9)1.6 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.1.7 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.For specific safetyhazards,see Section 9.2.Referenced Documents2.1 ASTM Standards:B571 Practice for Qualitative Adhesion Testing of MetallicCoatingsC168 Terminology Relating to Thermal InsulationE408 Test Methods for Total Normal Emittance of SurfacesUsing Inspection-Meter Techniques3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 cold boundary temperature(CBT)The cold bound-ary temperature,or cold side,of the MLI system is thetemperature of the cold surface of the element being insulated.The CBT is often assumed to be the liquid saturation tempera-ture of the cryogen.The CBT can also be denoted as Tc.3.1.2 cold vacuum pressure(CVP)The vacuum level un-der cryogenic temperature conditions during normal operation,but typically measured on the warm side of the insulation.TheCVP can be from one to three orders of magnitude lower thanthe WVP for a well-designed cryogenic-vacuum system.1This guide is under the jurisdiction of ASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.21 on ReflectiveInsulation.Current edition approved Nov.1,2013.Published February 2014.Originallyapproved in 1973.Last previous edition approved in 2009 as C740/C740M 97(2009).DOI:10.1520/C0740_C740M-13.2The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.1.3 effective thermal conductivity(ke)The keis thecalculated thermal conductivity through the total thickness ofthe multilayer insulation system between the reported bound-ary temper