1、Designation: D6621 00 (Reapproved 2012)Standard Practice forPerformance Testing of Process Analyzers for AromaticHydrocarbon Materials1This standard is issued under the fixed designation D6621; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、 revision, the 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 serves as a practical guide for the perfor-mance testing of process stream analyz
3、ers specifically formeasuring chemical or physical characteristics of liquid aro-matic hydrocarbon materials for production or certification ofthese materials. The practice may be applicable to otherhydrocarbon stream analyzers as well.1.2 Only external methods (complete substitution of theprocess s
4、tream with a standard) of control sample introductionare included. Internal methods are beyond the scope of thispractice.1.3 Methods for resetting key operational parameters ofanalyzers to match predefined limits are provided by vendorsand are not included in this practice.1.4 Analyzer validation pr
5、ocedures are covered in PracticesD3764 and D6122, not in this practice.1.5 Procedures for statistically interpreting data from auto-matic sampling process stream analyzers are outlined.1.6 The implementation of this practice requires that theanalyzer be installed according to APIRP-550 (1)2, and be
6、inagreement with the analyzer suppliers recommendations.Also, it assumes that the analyzer is designed to monitor thespecific material parameter of interest, and that at the time ofinitial or periodic validation, the analyzer was operating at theconditions specified by the manufacturer and consisten
7、tly withthe primary test method.1.7 The units of measure used in this practice shall be thesame as those applicable to the test primary method used foranalyzer validation.1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility
8、 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:3D3764 Practice for Validation of the Performance of ProcessStream Analyzer SystemsD4177 Practice for
9、 Automatic Sampling of Petroleum andPetroleum ProductsD6122 Practice for Validation of the Performance of Multi-variate Online, At-Line, and Laboratory Infrared Spectro-photometer Based Analyzer SystemsE456 Terminology Relating to Quality and StatisticsE1655 Practices for Infrared Multivariate Quant
10、itativeAnalysis3. Terminology3.1 Definitions:3.1.1 accuracy, ncloseness of agreement between a testresult and an accepted reference value.3.1.2 analyzer output, nsignal that is proportional to thequality parameter being measured and suitable for input toreadout instrumentation.3.1.2.1 DiscussionIt m
11、ay be pneumatic, electrical, digital,etc., and expressed as psi, mv, sec., etc.3.1.3 analyzer result, nnumerical estimate of a physical,chemical, or quality parameter produced by applying thecalibration model to the analyzer output signal.3.1.4 bias, nthe difference between the expectation of theres
12、ults and an accepted reference value.3.1.5 control sample, nmaterial similar to the processstream that is stable over long periods of time so that itsparameters may be measured reproducibly in performance teststo characterize analyzer precision and accuracy.3.1.5.1 DiscussionMay be a pure compound,
13、standardmixture, or a sample from the process stream. Its parameters1This practice is under the jurisdiction of ASTM Committee D16 on AromaticHydrocarbons and Related Chemicals and is the direct responsibility of Subcom-mittee D16.09 on On-Line Analysis.Current edition approved June 1, 2012. Publish
14、ed August 2012. Originallyapproved in 2000. Last previous edition approved in 2006 as D6621 00 (2006)1.DOI: 10.1520/D6621-00R12.2The boldface numbers in parentheses refer to the list of references at the end ofthis practice.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcont
15、act 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 Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1are used to plot statis
16、tical process control charts to defineanalyzer precision in normal operation.3.1.6 external performance testing, nprocedure involvingcomplete substitution of the process/product stream measuredby the analyzer with a control sample stream to measure theanalyzers precision and possibly accuracy (if th
17、e controlsamples true value is known).3.1.7 internal performance testing, nprocedure involvingthe addition of a known quantity of a standard materialhomogeneously into the process/product stream measured bythe analyzer to measure the analyzers precision and possiblyaccuracy (if the sample materials
18、true value is known).3.1.8 linearity, nparameter ranges where the analyzersresults do and do not approximate a straight line.3.1.9 performance testing of an analyzer, n mechanicaland statistical procedure for routinely checking the accuracyand precision of an analyzers results against historical acc
19、u-racy and precision for a control sample.3.1.10 precision, ncloseness of agreement of independenttest results of the same chemical or physical property of a givenmaterial obtained under stipulated conditions.3.1.10.1 DiscussionExpressed in terms of dispersion oftest results around the arithmetic me
20、an, usually as variance,standard deviation, repeatability or reproducibility, or both.3.1.11 repeatability of an analyzer, ndifference betweentwo successive analyzer results measured in a short timeinterval that would be exceeded in the long run in only 1 casein 20 (5 % of the time) when the analyze
21、r is operated on aflowing sample of uniform quality.3.1.12 reproducibility of an analyzer, n difference be-tween a single result from each of two identical analyzersystems that would be exceeded in the long run in only 1 casein 20 (5 % of the time) when the two systems are operated atdifferent sites
22、 by different operators, but on identical samples.3.1.13 rule violation, ncondition when a point value orpattern of points in a statistical process control chart statisti-cally exceeds the defined probability of its occurrence, asdefined by the Western Electric rules (2) being used.3.1.14 spot sampl
23、e, nrepresentative material resemblingthe stream being monitored, an identical portion of which isanalyzed both in a process analyzer and by a laboratory test ona non-scheduled basis for periodic validation testing.3.1.14.1 DiscussionMay be the same material as thecontrol sample.3.1.15 validation of
24、 an analyzer, nprocess to identify howcomparable an analyzers results are statistically to results fromthe primary method, or to define how the analyzers resultscompare to the primary methods results in precision andaccuracy.3.1.15.1 DiscussionMust be done when the analyzer isfirst configured or rec
25、onfigured (initial validation), and then ona periodic basis (periodic validation), as described in PracticeD3764.3.2 For additional definitions, see Appendix X1.4. Summary of Practice4.1 This practice standardizes aromatic hydrocarbonprocess-analyzer performance testing practices, or processesfor ma
26、intaining accurate and precise analyzer measurements. Itis used with methods for the measurement and certification ofaromatic hydrocarbon materials applied to continuous on-lineanalyzers. These methods are generally under the control ofCommittee D16 on Aromatic Hydrocarbons and RelatedChemicals. It
27、is meant as a practical guide for persons settingup and maintaining these analyzers in a process (non-laboratory) environment. They should apply it, with theirknowledge of the analyzers operation and of how the processanalyzer results are to be used, to maintain and optimizeanalyzer operation.5. Sig
28、nificance and Use5.1 Performance testing of on-line analyzers is critical totheir proper performance within predictable levels of precisionand accuracy. This practice can affect production efficiency andcertification of aromatic hydrocarbon materials.6. System Components6.1 Process analyzers for mea
29、suring the chemical composi-tion of aromatic hydrocarbons, their purity, or physical prop-erties often replace existing laboratory test methods, using thesame or similar chemical measurement techniques. Fig. 1shows several possible analyzer configurations for on-lineprocess testing of aromatic hydro
30、carbon materials. Aromatichydrocarbon stream analyzers are often based on chromatog-raphy, but they may also perform physical measurements, wetchemistry, or other methods described in new or existingCommittee D16 methods. This practice is intended to begenerally applicable to any of them.7. Performa
31、nce Guidelines Before Calibration7.1 At startup, validate any process analyzer against anexisting analytical method, typically in this case, one overseenby Committee D16.7.2 The capability measurement (cm) for a given analyzer(3) shall be less than 0.2, as defined in Eq 1:cm5sa2/sp2,0.2 (1)where:sa=
32、 standard deviation of the analyzer measurement, andsp= standard deviation of the process.The variance (standard deviation squared) of the analyzershould be less than 20 % of the variance of the process, so thatthe analyzer measurement can be useful for detecting changesin the process. The expected
33、capability for a process analyzermeasurement may be available from the vendor for a specificapplication before installation of the analyzer (advertisedanalyzer capability). Actual process stream measurement ca-pability should be measured on the process/product stream,usually after initial analyzer v
34、alidation.7.3 Automated analyzer sampling practices for aromatichydrocarbon liquid streams shall follow those referenced inPractice D4177.D6621 00 (2012)27.4 Determine the linearity of the process analyzer by usingat least three calibration standard materials with knowncompositions/responses for the
35、 components of interest. Eachcomponent should be present at a high, low, and mediumconcentration/amount level with respect to the concentration/amount range expected for the parameter (analyzer operatingrange). A plot of the component concentration/amount versusanalyzer response will determine if th
36、e analyzer has a linearresponse over the concentration range of interest. If analyzerresponse is nonlinear, additional calibration standards must beanalyzed to clearly determine the nonlinear behavior of eachanalyzer and component, if the analyzer is to be used in thenonlinear range.7.5 If a process
37、 analyzer is to be used only for trendinformation, the data generated by it is in a form that does notimpart compositional information, but relative informationonly, that is, peak area, peak height, counts, millivolts, etc.Initial validation and frequent performance testing are stillrequired to defi
38、ne precision, as well as to maintain properanalyzer operation.8. Performance Test Procedure8.1 Determine analyzer performance using external checksamples, which are substituted for the process material streamduring performance test runs.8.2 Process analyzers are routinely performance tested byusing
39、control samples. These may be primary or secondarystandard materials, or actual portions from the process stream.These portions must be representative of normal processconditions, and be stored to remain physically and chemicallystable over time. The control sample should be repeatedlyanalyzed by th
40、e process analyzer, and then using statisticalprocess control (SPC), to define the actual analyzer resultsprecision.8.3 Analyzer performance test frequency can be done at afixed time interval, based on analyzer reliability and operatorexperience. Typically, once per shift, day, or week are used, but
41、it may be more or less frequent. Unscheduled control sampleanalyses may be performed whenever the unit operator feelsthat something has changed in the process or process analyzer,or at a convenient time.8.4 The control sample material container shall be located ata point in the process to allow for
42、its simple and regularintroduction into the process analyzers sample introductionsystem (if appropriate) by the process operator. A sufficientquantity must be available for many repetitive analyses.8.5 Perform an external analyzer performance test byswitching the analyzer sample source from the proc
43、ess streamto the control sample, followed by sampling and analysis of thecontrol sample.8.6 Monitor the analyzers output from the control sampleuntil it stabilizes, that is, the difference between successivereadings is at or below the repeatability of the analyzer, (whichis measured as described in
44、8.10). If this does not occur, therepeatability of the analyzer has changed and should beremeasured.8.7 After stabilization of the analyzer, measure at least threesuccessive results on the control sample and average theresults. Plot the average of these three results in a SPC chartusing any statisti
45、cally correct method of data handling andcontrol chart construction (4).FIG. 1 Possible Process Analyzer ConfigurationsD6621 00 (2012)38.8 SPC charts of the control sample data shall be used tohelp decide if the analyzer needs to have its response param-eters reset, (5) or if it is working within pr
46、evious statisticallevels and should be left alone. SPC results and operatorexperience should be used to determine subsequent actions,such as determining the cause for any rule violation andcorrecting it.8.9 SPC charts of control samples help the operator todifferentiate between normal (random) and a
47、bnormal (nonran-dom) analyzer variation due to changes in analyzer operation.8.9.1 Charts may be maintained manually or with commer-cially available SPC software, preferably as part of the ana-lyzer data acquisition and control software.8.9.2 Control limits should be set at three (3) sigma (stan-dar
48、d deviations) from the mean value, warning limits at two (2)sigma, and suitable Western Electric rules (2) invoked, consis-tent with plant/facility statistical policy.8.9.3 All rule violations shall be investigated and eliminatedif possible, with all causes and actions documented with thecharts.8.9.
49、4 If a cause cannot be determined, analyzer operationshould continue without any parameter adjustment until thenext performance test.8.9.5 If there are no rule violations, analyzer parameteradjustment is not needed.8.9.6 If a rule violations cause is determined and elimi-nated, and if the operator feels that the analyzers accuracy haschanged as a result, proceed to reset analyzer parameters, asdiscussed in Section 9. If precision needs to be redefined forthe analysis process, follow the procedure listed in 8.10.8.10 To determine the repeatabili
