1、Designation: C 795 08Standard Specification forThermal Insulation for Use in Contact with AusteniticStainless Steel1This standard is issued under the fixed designation C 795; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This specification covers non-met
3、allic thermal insula-tion for use in contact with austenitic stainless steel piping andequipment. In addition to meeting the requirements specified intheir individual material specifications, issued under the juris-diction of ASTM Committee C16, these insulations must passthe preproduction test requ
4、irements of Test Method C 692, forstress corrosion effects on austenitic stainless steel, and theconfirming quality control, chemical requirements, when testedin accordance with the Test Methods C 871.1.2 The values stated in inch-pound units are to be regardedas standard. The values given in parent
5、heses are mathematicalconversions to SI units that are provided for information onlyand are not considered 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
6、 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 168 Terminology Relating to Thermal InsulationC 390 Practice for Sampling and Acceptance of ThermalInsulation LotsC 692 Test Method for Evaluating the Inf
7、luence of ThermalInsulations on External Stress Corrosion Cracking Ten-dency of Austenitic Stainless SteelC 871 Test Methods for Chemical Analysis of ThermalInsulation Materials for Leachable Chloride, Fluoride,Silicate, and Sodium Ions3. Terminology3.1 DefinitionsTerminology C 168 applies to the te
8、rmsused in this specification.3.2 Definitions of Terms Specific to This Standard:3.2.1 basic material specificationany of the materialspecifications for homogeneous insulation covered in any ofthe pertinent Annual Book of ASTM Standards.3.2.2 lota lot shall be defined in accordance with PracticeC 39
9、0 by agreement between the purchaser and the manufac-turer.3.2.3 stress corrosion cracking (SCC)the failure of metal,taking the form of cracks that potentially occur under thecombined influence of certain corrosive environments andapplied or residual stresses.3.2.4 wicking-type insulationinsulation
10、material that, byvirtue of its physical characteristics, permits a wetting liquid toinfiltrate it by capillary attraction.4. Significance and Use4.1 Stress corrosion cracking of austenitic stainless steel is ametallurgical phenomenon. One cause of stress corrosioncracking is the presence of contamin
11、ants in water solution,which can be concentrated at the stressed surface by evapora-tion of the water.4.2 There is an apparent correlation between stress corro-sion cracking of austenitic stainless steel and the use ofinsulation which either contains water-leachable chloride or, byreason of its wate
12、r absorptivity, acts as a vehicle through whichchlorides from outside the system are concentrated at thesurface of the stainless steel.3,4,54.3 Studies have shown that insulation containing certainwater-soluble compounds have the capacity to retard or prevent1This specification is under the jurisdic
13、tion of ASTM Committee C16 onThermal Insulation and is the direct responsibility of Subcommittee C16.20 onHomogeneous Inorganic Thermal Insulations.Current edition approved Oct. 15, 2008. Published November 2008. Originallyapproved in 1977. Last previous edition approved in 2003 as C 795 03.2For ref
14、erenced 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.3Schaffer, L. D., and Klapper, J. A., “Investigation of the Effects o
15、f Wet,Chloride-Bearing, Thermal Insulation on Austenitic Stainless Steel,” Report No.ESI-25-(a)-1, Oak Ridge National Laboratory, and Ebasco Services Inc., November1, 1961.4Dana, A. W., Jr., “Stress-Corrosion Cracking of Insulated Austenitic StainlessSteel,” ASTM Bulletin, October 1957.5Louthan, M.
16、R., Jr., “Initial Stages of Stress Corrosion Cracking in AusteniticStainless Steels,” Corrosion, NACE, September 1965.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.stress corrosion. Numerous materials thought to inhibit stresscorro
17、sion cracking have been tried with varying degrees ofsuccess. An inhibiting compound commonly used is sodiumsilicate. Present knowledge indicates that the sodium silicatedissociates in the presence of water, leaving the silicate ion toform a protective mechanism that inhibits or prevents thechloride
18、 ion from attacking the stainless steel. Under adverseenvironmental conditions, this protective agent will possibly beleached from the product with time and permanent protectionis not afforded.4.4 Test Method C 692 contains a procedure for determiningwhether or not stress corrosion cracking will occ
19、ur with a giventhermal insulation. The procedure is used to evaluate insulationmaterials have the potential to inhibit, to be passive, or activelycontribute to stress corrosion cracking of austenitic stainlesssteels.4.5 Research has indicated that in addition to the halide ionchloride, fluoride ions
20、 have the potential to induce SCC in theabsence of inhibiting ions.6Two widely used insulation speci-fications that are similar to C 795 and are specific to SCC allowthe use of the same Test Methods C 692 and C 871 forevaluation of insulation materials. Both specifications requirefluoride ions to be
21、 included with chloride ions when evaluatingthe extractable ions and plotting them on the Fig. 1 acceptabil-ity graph. Fluoride has been added to chloride in Section 13and on Fig. 1 to be consistent with the other standards.4.6 Physical and chemical changes can occur when thermalinsulation, various
22、binders, or adhesives, or a combinationsthereof, are heated. Insulation materials are often exposed toprocess temperatures that are sufficient to cause changes.Various compounds thermally decompose increasing the solu-bility of some ions that leach out when exposed to water. Othercompounds have the
23、potential to become less soluble afterthermal exposure.4.7 The inhibitory qualities of sodium silicate compoundshave been found to be different for different molar ratios ofsodium to silicate. The current specifications treat them asbeing added together for a total ppm value.64.8 A variety of acids
24、and ionic chemical solutions areknown to induce metal pitting, hydrogen embrittlement, inter-granular corrosion and stress corrosion cracking on sensitizedaustenitic stainless steel. The results of Test Methods C 692corrosion test are expected to indicate if there is an untestedagent in the insulati
25、on that will induce cracking.5. Ordering Information5.1 The requirements of this specification shall be stated bythe purchaser for the particular insulation and material appli-cation specified. The purchaser shall specify the type, grade,class, dimensions, quantity, and other requirements as availab
26、lein the basic material specification for a particular insulation.6Whorlow, Kenneth M., Woolridge, Edward and Hutto, Francis B., Jr., “Effect ofHalogens and Inhibitors on the External Stress Corrosion Cracking of Type 304Austenitic Stainless Steel”; STP 1320 Insulation Materials: Testing and Applica
27、-tions, Third Volume, Ronald S. Graves and Robert R. Zarr, editors, ASTM WestConshohocken, PA, 1997 page 485 .FIG. 1 Acceptability of Insulation Material on the Basis of the Plot Points of the (Cl + F) and the (Na + SiO3) Analyses.C7950826. Composition6.1 The material shall conform to the establishe
28、d require-ments of the basic material specification.7. Physical and Chemical Requirements7.1 The physical requirements shall conform to the require-ments of the basic material specification. The chemical require-ments shall conform to the requirements of Section 13 of thisspecification.8. Dimensions
29、 and Permissible Variations8.1 The dimensions and permissible variations shall con-form to the requirements of the basic material specification.9. Workmanship, Finish, and Appearance9.1 The workmanship, finish, and appearance shall conformto the requirements of the basic material specification.10. S
30、ampling10.1 The unit sample shall be of sufficient size to performthe preproduction corrosion test and chemical analysis testsspecified in this specification. The samples shall be of sufficientsize to ensure an acceptable level of confidence that the testresults represent the characteristics of the
31、product beingpurchased. Sample size shall be in accordance with PracticeC 390.11. Acceptance and Retests11.1 AcceptanceAll specimens in a lot sampling shallmeet the chemical requirements of this specification. If theaverage analysis of the two specimens taken from any samplefails to conform to the r
32、equirements of this specification, the lotrepresented by that sample shall be rejected.11.2 RetestAt the option of the supplier, each individualunit of supply (that is, carton, bag, roll, sheet, drum, and soforth) in rejected lots are allowed to be retested, in accordancewith Test Methods C 871, at
33、the suppliers expense, by testingsamples taken at random from the unit of supply in accordancewith this specification. Unless otherwise agreed upon betweenthe purchaser and the manufacturer, the resubmitted materialshall require the same number of samples to be tested asrequired for the initial subm
34、ittal. If the average analysis of thetwo specimens taken from each sample fails to conform to therequirements of this specification, the unit of supply repre-sented by that sample shall be rejected. For other than chemicalanalysis or stress corrosion tests, the number of tests and retestsshall be as
35、 specified in the basic material specification.12. Preproduction Corrosion Test12.1 A corrosion test shall be performed as a preproductiontest by each manufacturer. The production lot from which thesample is taken shall be of the same formulation, made by thesame production processes and from the sa
36、me kind, nature, andquality of ingredients as those that will be employed forproduction of thermal insulation under this specification.12.2 The corrosion test shall be conducted in accordancewith the method presented in Test Method C 692. At the end ofthe test time, none of the prepared coupons of s
37、tainless steelshall show a crack when examined in accordance with TestMethod C 692.12.3 The test procedure need not be repeated for subsequentorders using the same production process and the same kind,nature, and quality of ingredients unless so required. Themanufacturer shall keep records of actual
38、 numerical results ofthe tests available for review on request by those concerned.13. Chemical Analysis13.1 A chemical analysis shall be performed on the insula-tion material in accordance with Test Methods C 871 and, inaddition, the manufacturer shall demonstrate that his currentproduct has passed
39、the preproduction corrosion test in accor-dance with Test Method C 692.13.1.1 An acceptable proportion of sodium plus silicate ionsto the chloride plus fluoride ions as found by leaching from theinsulation is shown in Fig. 1 and was arrived at empirically.Other insulation compositions, whose chemica
40、l analysis fallsoutside of the acceptance area shown in Fig. 1, are possiblyacceptable; however, their efficacy shall be determined inaccordance with Test Method C 692 and subsequently moni-tored in accordance with Test Methods C 871.13.2 pHThe pH of the leach water extracted, in accor-dance with Te
41、st Method C 871, shall be measured using a pHmeter and probe and shall have a pH no greater than 12.5 at77F (25C).13.3 The specific material supplied shall be analyzed inaccordance with Test Methods C 871 for the following leach-able ions: chloride, fluoride, sodium, and silicate. The “plotpoint” of
42、 these analyses shall fall in the acceptable area of Fig.1.13.4 The minimum allowable value of sodium plus silicateshall be 50 ppm. There is no minimum limit on chloride plusfluoride. Extrapolating the chloride plus fluoride level below10 ppm on Fig. 1 is considered to be in the acceptable areawhen
43、the sodium and silicate is above 50 ppm.14. Handling and Application14.1 See applicable ASTM specifications for handling andapplication.15. Keywords15.1 austenitic stainless steel; chloride; fluoride; pH; sili-cate; sodium; stress corrosion cracking; thermal insulationC795083ASTM International takes
44、 no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own resp
45、onsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addresse
46、d to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the
47、address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).C795084
