ASTM D6796-02(2008)
(Practice)Standard Practice for Production of Coal, Coke and Coal Combustion Samples for Interlaboratory Studies
Standard Practice for Production of Coal, Coke and Coal Combustion Samples for Interlaboratory Studies
SIGNIFICANCE AND USE
The objective of this practice is to provide guidelines for the preparation of samples for interlaboratory studies to evaluate new test methods or for quality control purposes.
These samples prepared using these guidelines may be used for the testing of the precision and bias mandatory for ASTM test methods. Such an evaluation is necessary to provide guidance to the user as to the reliability of measurements that can be expected by its use. The statements are developed on the basis of user experience (ordinarily through interlaboratory studies) with the test method.
The availability of appropriate samples is a key requirement for interlaboratory studies.
The homogeneity of the sample produced for interlaboratory studies must be small enough so that the variance caused by the sample is small compared to the variance of the test being performed.
SCOPE
1.1 This practice describes the essential activities that are required to produce samples for interlaboratory studies.
1.2 The suitability of a particular interlaboratory sample developed using this guide will depend on the tests being made.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: D6796 − 02(Reapproved 2008)
Standard Practice for
Production of Coal, Coke and Coal Combustion Samples for
Interlaboratory Studies
This standard is issued under the fixed designation D6796; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope D5142Test Methods for ProximateAnalysis of theAnalysis
Sample of Coal and Coke by Instrumental Procedures
1.1 This practice describes the essential activities that are
(Withdrawn 2010)
required to produce samples for interlaboratory studies.
D5263Test Method for Determining the Relative Degree of
Oxidation in Bituminous Coal by Alkali Extraction
1.2 The suitability of a particular interlaboratory sample
E178Practice for Dealing With Outlying Observations
developed using this guide will depend on the tests being
E691Practice for Conducting an Interlaboratory Study to
made.
Determine the Precision of a Test Method
1.3 This standard does not purport to address all of the
E826Practice for Testing Homogeneity of a Metal Lot or
safety concerns, if any, associated with its use. It is the
Batch in Solid Form by Spark Atomic Emission Spec-
responsibility of the user of this standard to establish appro-
trometry
priate safety and health practices and determine the applica-
3. Terminology
bility of regulatory limitations prior to use.
3.1 Definitions—For definitions of terms used in this
2. Referenced Documents
practice, refer to Terminology D121.
2.1 ASTM Standards:
4. Summary of Practice
D121Terminology of Coal and Coke
4.1 Test samples of adequately defined composition and
D346 Practice for Collection and Preparation of Coke
homogeneity are required for interlaboratory studies. These
Samples for Laboratory Analysis
samples should be typical in all respects to the samples for
D2013Practice for Preparing Coal Samples for Analysis
which the test method is applicable.
D2234/D2234MPractice for Collection of a Gross Sample
4.1.1 Thesampleshouldbeofsufficientquantitytoperform
of Coal
all necessary tests and replicates. Guidelines specifying mini-
D2492Test Method for Forms of Sulfur in Coal
mum quantities are given in Practice D2013.
D2961Test Method for Single-Stage Total Moisture Less
4.1.2 The top size must be consistent for the test being run.
than 15 % in Coal Reduced to 2.36-mm (No. 8 Sieve)
4.2 Differences in results due to the homogeneity or
Topsize
oxidation, or both, of the test sample should be minimal with
D3172Practice for Proximate Analysis of Coal and Coke
respect to other errors.
D3173Test Method for Moisture in theAnalysis Sample of
Coal and Coke
5. Significance and Use
D3302Test Method for Total Moisture in Coal
5.1 Theobjectiveofthispracticeistoprovideguidelinesfor
D4596Practice for Collection of Channel Samples of Coal
the preparation of samples for interlaboratory studies to evalu-
in a Mine
ate new test methods or for quality control purposes.
5.2 These samples prepared using these guidelines may be
used for the testing of the precision and bias mandatory for
This practice is under the jurisdiction of ASTM Committee D05 on Coal and
ASTM test methods. Such an evaluation is necessary to
Coke and is the direct responsibility of Subcommittee D05.24 on Statistics.
Current edition approved Feb. 1, 2008. Published March 2008. Originally
provide guidance to the user as to the reliability of measure-
approved in 2002. Last previous edition approved in 2002 as D6796–02. DOI:
ments that can be expected by its use. The statements are
10.1520/D6796-02R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on The last approved version of this historical standard is referenced on
the ASTM website. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6796 − 02 (2008)
based on acceptable test results for each material from fewer than 6
developed on the basis of user experience (ordinarily through
laboratories.
interlaboratory studies) with the test method.
NOTE 3—In preparing an interlaboratory sample, the range of values of
5.3 The availability of appropriate samples is a key require-
the property being measured should be considered, the ranks of coal to
which the method will be applied, the difficulty and expense of preparing
ment for interlaboratory studies.
anddistributingsamples,thelengthoftimeandexpenseinperformingthe
5.4 The homogeneity of the sample produced for interlabo-
test and the commercial or legal need for reliable estimates of precision
ratorystudiesmustbesmallenoughsothatthevariancecaused when choosing the number of materials to be used.
by the sample is small compared to the variance of the test
7. Determining the Suitability of the Sample for the Test
being performed.
Method
6. Sample Selection and Preparation
7.1 After the sample has been prepared, or if a previously
6.1 Collect samples using Practice D2234/D2234M, Prac-
prepared sample is to be used for tests other than for what it
tice D4596 for coal, or D346 for coke. Coal combustion
was originally prepared, the homogeneity of the sample must
products should be sampled in a manner to provide a repre-
be determined.
sentative sample free from contamination. The sample should
7.2 Test samples must be sufficiently homogeneous to
be typical of a certain class of samples (for example, Eastern
evaluate the test method.The degree of homogeneity is related
U.S.bituminouscoal)oracertainvalueforacomponent(such
to the size of the sample analyzed. Hence the minimum size of
as coals with two percent sulfur), or both, so that appropriate
a sample meeting a specified homogeneity must be stated, and
diversity of samples can be identified for interlaboratory
this must be equal to or smaller than the size of the sample
studies. See Note 1.
specified in the test method. Also, different tests may require
6.2 Grind samples to the proper size required by the test
different sample sizes to achieve homogeneity. Tests for
method and properly homogenize and split. Prepare samples
homogeneity should be made. An acceptable method for
usingPracticeD2013.Somecoalcombustionproductsmaynot
measuring homogeneity is given in Appendix X1.
require grinding, but tests should be run to determine if further
7.3 The uncertainties in homogeneity, moisture, or sample
grinding is necessary.
composition, or a combination thereof, should not exceed one
6.3 Both single-laboratory precision and between operator-
third of the measurement uncertainties they are expected to
laboratory precision should be evaluated. Material of adequate
evaluate. When this specification is met, sample uncertainties
homogeneity but of uncertain composition may be used to
make a negligible contribution to the variance of the test
determine precision of a given test method.
results. While replicate samples may be used in practical
NOTE 1—The use of materials of demonstrated adequate homogeneity
analysistoaverageoutsamplevariations,thisisnotfeasiblein
and known value for the test enables evaluation of the precision and bias
the case of samples for Interlaboratory Studies; hence, homo-
of a test method. Materials of known value for the test are required to
geneity should be attained as far as possible.
identify biases. Consensus values obtained as the result of interlaboratory
studies are not adequate to permit quantitative evaluation of biases,
7.4 Samples not meeting the homogeneity requirements
although they may show that such exist.
above for a given test should not be used in interlaboratory
6.4 Usesixormorematerialsforeachinterlaboratorystudy.
studies unless they are re-mixed (all samples must be recom-
See Notes 1-3.
bined and the entire sample rehomogenized, see 6.2) and
6.5 Eachlaboratoryshallreceiveitsownsampleandatleast retested. In some cases, samples that are inhomogeneous for
one test may be homogeneous for other tests.
one sample shall be archived by the interlaboratory study
coordinator.
7.5 Top size of the sample must be consistent with required
top size or reduced to the appropriate size.
6.6 The bulk sample should be available in sufficient quan-
tity for the requirements of the interlaboratory study, to test for
7.6 Sample stability may be determined. See Note 4.
homogeneity and to permit further examination by other
7.6.1 Moisture—For most tests moisture should be deter-
techniques.
mined and compared to other results and calculated to a
common basis.
6.7 Sample preparation and distribution should provide
7.6.2 Oxidation—Coals (particularly those of low rank)
enough material and time so that laboratories can perform test
runs on new or unfamiliar methods. This is very important storedforalongperiodoftimemaybecomeoxidized.Ifpyrite
becomes oxidized it may affect forms of sulfur determinations
because only laboratories that are thoroughly familiar and
experienced with the procedure can be considered qualified to (see Test Methods D2492). Bituminous coals are generally
stable for long periods of time but the degree of oxidation of
participate in the interlaboratory study.
bituminouscoalscanbedeterminedusingTestMethodD5263.
6.8 Sample stability (see 7.6), storage and future accessibil-
ity should be considered.
8. Sample Storage and Preservation
NOTE 2—Practice E691 paragraph 10.2.2 states, “An interlaboratory
study of a test method should include at least three materials, and for
8.1 Samples should be stored in such a way to maintain
development of broadly applicable precision statements, six or more
sample stability for the characteristics being measured. See
materials should be included in the study.” Because of the peculiarities of
Note 4.
different ranks of coal, more than the minimum six materials are needed
8.1.1 Changes of values in ultimate analysis should be less
to develop precision statements applicable to all coal types. Under no
circumstances should the final statement of precision of a test method be than 1% over a 10 year period.
D6796 − 02 (2008)
significant change of most coal characteristics.
8.1.2 Moisture should be determined by an appropriate
NOTE 5—Lower rank coals (subituminous and lignite) generally have
method (D3172, D3173, D5142, D3302,or D2961) prior to
high moisture content and oxidize rapidly. This oxidation may continue
each analysis. It should not be assumed that moisture content
formonthsbutwillslowwithtime.Moisturevaluesinthesesamplesmay
will remain constant from day to day especially for low rank
depend on the time the sample is taken and the relative humidity of the
coals.
laboratory and may change within seconds after the sample is removed
from the bottle and over a longer period of time within the bottle.
8.1.3 Exceptformoisture,thelargestabsolutedifferencesin
parametervaluechangesarelikelytobeforpercentcarbondue
9. Record Keeping
to oxidation.
9.1 Characteristics of the sample should be recorded. At a
8.1.4 For less stable coals or coals with high moisture
minimumtherank,percentash,topsize,approximatemoisture
contents, or both, more aggressive storage or preservation
content, special handling comments, amount of sample avail-
procedures may be employed. See Note 5.
able and original purpose for which the standard was collected
8.2 Samples may be conditioned (preoxidized) prior to
shall be recorded. Sample location, sample type (run of mine;
splitting and bottling. See Appendix X2.
D121, channel sample; D4596, etc). Maintain all results with
8.2.1 Samples may be stored under nitrogen or argon to
the samples until they are published, at which time only the
minimizeoxidation.Nitrogenischeaperbutargonislesslikely
reference need be maintained.
to react with coal components.
9.2 Recordwhenthesamplewascollected,recordwhenthe
8.2.2 Samples may be refrigerated to minimize oxidation.
sample was prepared, and record how the sample has been
Samples should be maintained at about 4°C. Care must be
maintained.
taken to minimize changes in moisture. It is not recommended
thatsamplesbefrozenasthismightchangetoporestructureof
9.3 A list of samples currently available with the informa-
the coal.
tion listed in 8.1 and 8.2 should be accessible to interested
8.2.3 Depending on the characteristics of the coal to be
parties who may wish to use them for interlaboratory studies.
measured, high moisture coals may be stored in water.
NOTE 4—Storing samples in darkness or brown bottles can reduce
10. Keywords
photochemical changes. Air-dried relatively stable-low moisture coals,
10.1 ash; coal; coke; combustion residue; homogeneity;
coke and stable combustion products can be stored in tightly sealed glass
or plastic containers at room temperature for long periods of time without laboratory; moisture; oxidation; quality control
APPENDIXES
(Nonmandatory Information)
X1. TEST FOR HOMOGENEITY
X1.1 Test for homogeneity shall be conducted by a single X1.1.4 Label all containers consecutively (that is, 01, 02,
laboratory in a manner similar to that given in Practice E826 03, .c). If all sample containers will not be measured (see
prior to sample distribution. X1.1.3) select the containers to be measured as follows: From
a table of random numbers (see Table X1.1 and the Warning
X1.1.1 Conduct all tests by the best available procedure
note below ) pick an arbitrary starting place and select any
under optimum conditions. Preferably a method with a known
direction for reading the numbers provided the direction is
precision and bias shall be used.
fixed in advance and is independent of the numbers occurring.
X1.1.2 If the samples have been split into less than 15
Select those containers for testing that match the numbers read
laboratory samples, sub-samples from each laboratory sample
from the tables.
shall be measured for the test of interest.
Warning—Table X1.1 included herein is for example, only.
X1.1.2.1 Whenever possible the test portions should be
Use the more complete table in when actually using this test
takenonlyafterthelaboratorysamplesisrolledinitscontainer
procedure.
at least 5 turns followed by inverting the sample 5 times.
X1.1.5 Whenever possible at least 4 separate sub-samples
(1) This process should be repeated at least 3 times.
taken from each container and labeled with the container
(2) A sample can then be taken from the top.
number and sub- sample number (that is, 02-1 for container 02
X1.1.2.2 The steps in X1.1.2.1 should be repeated for all
sub-sample 1)
...
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