1、Designation: D6796 16Standard Practice forProduction of Coal, Coke and Coal Combustion Samples forInterlaboratory Studies1This standard is issued under the fixed designation D6796; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, th
2、e year 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.1. Scope1.1 This practice describes the essential activities that arerequired to produce samples for interlaboratory stu
3、dies.1.2 The suitability of a particular interlaboratory sampledeveloped using this guide will depend on the tests beingmade.1.3 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all o
4、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:2D121 Terminology of Coa
5、l and CokeD346/D346M Practice for Collection and Preparation ofCoke Samples for Laboratory AnalysisD2013/D2013M Practice for Preparing Coal Samples forAnalysisD2234/D2234M Practice for Collection of a Gross Sampleof CoalD2492 Test Method for Forms of Sulfur in CoalD2961 Test Method for Single-Stage
6、Total Moisture Lessthan 15 % in Coal Reduced to 2.36-mm (No. 8 Sieve)TopsizeD3173 Test Method for Moisture in the Analysis Sample ofCoal and CokeD3302/D3302M Test Method for Total Moisture in CoalD4596 Practice for Collection of Channel Samples of Coalin a MineD5263 Test Method for Determining the R
7、elative Degree ofOxidation in Bituminous Coal by Alkali ExtractionD7582 Test Methods for Proximate Analysis of Coal andCoke by Macro Thermogravimetric AnalysisE178 Practice for Dealing With Outlying ObservationsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test
8、 MethodE826 Practice for Testing Homogeneity of a Metal Lot orBatch in Solid Form by Spark Atomic Emission Spec-trometry3. Terminology3.1 DefinitionsFor definitions of terms used in thispractice, refer to Terminology D121.4. Summary of Practice4.1 Test samples of adequately defined composition andho
9、mogeneity are required for interlaboratory studies. Thesesamples should be typical in all respects to the samples forwhich the test method is applicable.4.1.1 The sample should be of sufficient quantity to performall necessary tests and replicates. Guidelines specifying mini-mum quantities are given
10、 in Practice D2013/D2013M.4.1.2 The top size must be consistent for the test being run.4.2 Differences in results due to the homogeneity oroxidation, or both, of the test sample should be minimal withrespect to other errors.5. Significance and Use5.1 The objective of this practice is to provide guid
11、elines forthe preparation of samples for interlaboratory studies to evalu-ate new test methods or for quality control purposes.5.2 Samples prepared using these guidelines may be usedfor the testing of the precision and bias mandatory for ASTMtest methods. Such an evaluation is necessary to providegu
12、idance to the user as to the reliability of measurements thatcan be expected by its use. The statements are developed on thebasis of user experience (ordinarily through interlaboratorystudies) with the test method.5.3 The availability of appropriate samples is a key require-ment for interlaboratory
13、studies.1This practice is under the jurisdiction of ASTM Committee D05 on Coal andCoke and is the direct responsibility of Subcommittee D05.24 on Statistics.Current edition approved March 1, 2016. Published May 2016. Originallyapproved in 2002. Last previous edition approved in 2008 as D679602(2008)
14、.DOI: 10.1520/D6796-16.2For 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.Copyright ASTM International, 100 Barr
15、 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.4 The homogeneity of the sample produced for interlabo-ratory studies must be small enough so that the variance causedby the sample is small compared to the variance of the testbeing performed.6. Sample Selection and Prepa
16、ration6.1 Collect samples using Practice D2234/D2234M, Prac-tice D4596 for coal, or Practice D346/D346M for coke. Coalcombustion products should be sampled in a manner to providea representative sample free from contamination. The sampleshould be typical of a certain class of samples (for example,Ea
17、stern U.S. bituminous coal) or a certain value for a compo-nent (such as coals with two percent sulfur), or both, so thatappropriate diversity of samples can be identified for interlabo-ratory studies. See Note 1.6.2 Grind samples to the proper size required by the testmethod and properly homogenize
18、 and split. Prepare samplesusing Practice D2013/D2013M. Some coal combustion prod-ucts may not require grinding, but tests should be run todetermine if further grinding is necessary.6.3 Both single-laboratory precision and between operator-laboratory precision should be evaluated. Material of adequa
19、tehomogeneity but of uncertain composition may be used todetermine precision of a given test method.NOTE 1The use of materials of demonstrated adequate homogeneityand known value for the test enables evaluation of the precision and biasof a test method. Materials of known value for the test are requ
20、ired toidentify biases. Consensus values obtained as the result of interlaboratorystudies are not adequate to permit quantitative evaluation of biases,although they may show that such exist.6.4 Use six or more materials for each interlaboratory study.See Notes 1-3.6.5 Each laboratory shall receive i
21、ts own sample and at leastone sample shall be archived by the interlaboratory studycoordinator.6.6 The bulk sample should be available in sufficient quan-tity for the requirements of the interlaboratory study, to test forhomogeneity and to permit further examination by othertechniques.6.7 Sample pre
22、paration and distribution should provideenough material and time so that laboratories can perform testruns on new or unfamiliar methods. This is very importantbecause only laboratories that are thoroughly familiar andexperienced with the procedure can be considered qualified toparticipate in the int
23、erlaboratory study.6.8 Sample stability (see 7.6), storage and future accessibil-ity should be considered.NOTE 2Practice E691 paragraph 10.2.2 states, “An ILS of a testmethod should include at least three materials representing different testlevels, and for development of broadly applicable precisio
24、n statements, sixor more materials should be included in the study.” Because of thepeculiarities of different ranks of coal, more than the minimum sixmaterials are needed to develop precision statements applicable to all coaltypes. Under no circumstances should the final statement of precision ofa t
25、est method be based on acceptable test results for each material fromfewer than 6 laboratories.NOTE 3In preparing an interlaboratory sample, the range of values ofthe property being measured should be considered, the ranks of coal towhich the method will be applied, the difficulty and expense of pre
26、paringand distributing samples, the length of time and expense in performing thetest and the commercial or legal need for reliable estimates of precisionwhen choosing the number of materials to be used.7. Determining the Suitability of the Sample for the TestMethod7.1 After the sample has been prepa
27、red, or if a previouslyprepared sample is to be used for tests other than for what itwas originally prepared, the homogeneity of the sample mustbe determined.7.2 Test samples must be sufficiently homogeneous toevaluate the test method. The degree of homogeneity is relatedto the size of the sample an
28、alyzed. Hence the minimum size ofa sample meeting a specified homogeneity must be stated, andthis must be equal to or smaller than the size of the samplespecified in the test method. Also, different tests may requiredifferent sample sizes to achieve homogeneity. Tests forhomogeneity should be made.
29、An acceptable method formeasuring homogeneity is given in Appendix X1.7.3 The uncertainties in homogeneity, moisture, or samplecomposition, or a combination thereof, should not exceed onethird of the measurement uncertainties they are expected toevaluate. When this specification is met, sample uncer
30、taintiesmake a negligible contribution to the variance of the testresults. While replicate samples may be used in practicalanalysis to average out sample variations, this is not feasible inthe case of samples for Interlaboratory Studies; hence, homo-geneity should be attained as far as possible.7.4
31、Samples not meeting the homogeneity requirementsabove for a given test should not be used in interlaboratorystudies unless they are re-mixed (all samples must be recom-bined and the entire sample rehomogenized, see 6.2) andretested. In some cases, samples that are inhomogeneous forone test may be ho
32、mogeneous for other tests.7.5 Top size of the sample must be consistent with requiredtop size or reduced to the appropriate size.7.6 Sample stability may be determined. See Note 4.7.6.1 MoistureFor most tests moisture should be deter-mined and compared to other results and calculated to acommon basi
33、s.7.6.2 OxidationCoals (particularly those of low rank)stored for a long period of time may become oxidized. If pyritebecomes oxidized it may affect forms of sulfur determinations(see Test Method D2492). Bituminous coals are generallystable for long periods of time but the degree of oxidation ofbitu
34、minous coals can be determined using Test Method D5263.8. Sample Storage and Preservation8.1 Samples should be stored in such a way to maintainsample stability for the characteristics being measured. SeeNote 4.8.1.1 Changes of values in ultimate analysis should be lessthan 1 % over a 10 year period.
35、8.1.2 Moisture should be determined by an appropriatemethod (D3173, D7582, D3302/D3302M,orD2961) prior toeach analysis. It should not be assumed that moisture contentwill remain constant from day to day especially for low rankcoals.D6796 1628.1.3 Except for moisture, the largest absolute differences
36、 inparameter value changes are likely to be for percent carbon dueto oxidation.8.1.4 For less stable coals or coals with high moisturecontents, or both, more aggressive storage or preservationprocedures may be employed. See Note 5.8.2 Samples may be conditioned (preoxidized) prior tosplitting and bo
37、ttling. See Appendix X2.8.2.1 Samples may be stored under nitrogen or argon tominimize oxidation. Nitrogen is cheaper but argon is less likelyto react with coal components.8.2.2 Samples may be refrigerated to minimize oxidation.Samples should be maintained at about 4 C. Care must betaken to minimize
38、 changes in moisture. It is not recommendedthat samples be frozen as this might change to pore structure ofthe coal.8.2.3 Depending on the characteristics of the coal to bemeasured, high moisture coals may be stored in water.NOTE 4Storing samples in darkness or brown bottles can reducephotochemical
39、changes. Air-dried relatively stable-low moisture coals,coke and stable combustion products can be stored in tightly sealed glassor plastic containers at room temperature for long periods of time withoutsignificant change of most coal characteristics.NOTE 5Lower rank coals (subituminous and lignite)
40、 generally havehigh moisture content and oxidize rapidly. This oxidation may continuefor months but will slow with time. Moisture values in these samples maydepend on the time the sample is taken and the relative humidity of thelaboratory and may change within seconds after the sample is removedfrom
41、 the bottle and over a longer period of time within the bottle.9. Record Keeping9.1 Characteristics of the sample should be recorded. At aminimum the rank, percent ash, top size, approximate moisturecontent, special handling comments, amount of sample avail-able and original purpose for which the sa
42、mple was collectedshall be recorded. Sample location, sample type (run of mine;Terminology D121, channel sample; Practice D4596, etc).Maintain all results with the samples until they are published,at which time only the reference need be maintained.9.2 Record when the sample was collected, record wh
43、en thesample was prepared, and record how the sample has beenmaintained.9.3 A list of samples currently available with the informa-tion listed in 8.1 and 8.2 should be accessible to interestedparties who may wish to use them for interlaboratory studies.10. Keywords10.1 ash; coal; coke; combustion re
44、sidue; homogeneity;laboratory; moisture; oxidation; quality controlAPPENDIXES(Nonmandatory Information)X1. TEST FOR HOMOGENEITYX1.1 Test for homogeneity shall be conducted by a singlelaboratory in a manner similar to that given in Practice E826prior to sample distribution.X1.1.1 Conduct all tests by
45、 the best available procedureunder optimum conditions. Preferably a method with a knownprecision and bias shall be used.X1.1.2 If the samples have been split into less than 15laboratory samples, sub-samples from each laboratory sampleshall be measured for the test of interest.X1.1.2.1 Whenever possi
46、ble the test portions should betaken only after the laboratory samples is rolled in its containerat least 5 turns followed by inverting the sample 5 times.(1) This process should be repeated at least 3 times.(2) A sample can then be taken from the top.X1.1.2.2 The steps in X1.1.2.1 should be repeate
47、d for allsubsequent test portions even if they are taken from the samecontainer.X1.1.3 If the number of containers is so large that testportions from each container cannot be measured, a minimumof 8 % but not less than 15 should be tested for homogeneity.X1.1.4 Label all containers consecutively (th
48、at is, 01, 02,03, .c). If all sample containers will not be measured (seeX1.1.3) select the containers to be measured as follows: Froma table of random numbers (see Table X1.1 and the Warningnote below) pick an arbitrary starting place and select anydirection for reading the numbers provided the dir
49、ection isfixed in advance and is independent of the numbers occurring.Select those containers for testing that match the numbers readfrom the tables.WarningTable X1.1 included herein is for example, only.Use the more complete table in when actually using this testprocedure.X1.1.5 Whenever possible at least 4 separate sub-samplestaken from each container and labeled with the containernumber and sub- sample number (that is, 02-1 for container 02sub-sample 1). All sub-samples with the same extension (forexample, XX-1) shall be determined together as a sample setwith appropriat
