ASTM D6621-00(2012)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D6621 − 00 (Reapproved 2012)
Standard Practice for
Performance Testing of Process Analyzers for Aromatic
Hydrocarbon Materials
This standard is issued under the fixed designation D6621; 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 priate safety and health practices, and determine the applica-
bility of regulatory limitations prior to use.
1.1 This practice serves as a practical guide for the perfor-
mance testing of process stream analyzers specifically for
2. Referenced Documents
measuring chemical or physical characteristics of liquid aro-
2.1 ASTM Standards:
matic hydrocarbon materials for production or certification of
D3764PracticeforValidationofthePerformanceofProcess
these materials. The practice may be applicable to other
Stream Analyzer Systems
hydrocarbon stream analyzers as well.
D4177Practice for Automatic Sampling of Petroleum and
1.2 Only external methods (complete substitution of the
Petroleum Products
process stream with a standard) of control sample introduction
D6122Practice for Validation of the Performance of Multi-
are included. Internal methods are beyond the scope of this
variate Online,At-Line, and Laboratory Infrared Spectro-
practice.
photometer Based Analyzer Systems
1.3 Methods for resetting key operational parameters of
E456Terminology Relating to Quality and Statistics
analyzers to match predefined limits are provided by vendors
E1655 Practices for Infrared Multivariate Quantitative
and are not included in this practice.
Analysis
1.4 Analyzer validation procedures are covered in Practices
3. Terminology
D3764 and D6122, not in this practice.
3.1 Definitions:
1.5 Procedures for statistically interpreting data from auto-
3.1.1 accuracy, n—closeness of agreement between a test
matic sampling process stream analyzers are outlined.
result and an accepted reference value.
1.6 The implementation of this practice requires that the
2 3.1.2 analyzer output, n—signal that is proportional to the
analyzer be installed according to APIRP-550 (1), and be in
quality parameter being measured and suitable for input to
agreement with the analyzer supplier’s recommendations.
readout instrumentation.
Also, it assumes that the analyzer is designed to monitor the
3.1.2.1 Discussion—It may be pneumatic, electrical, digital,
specific material parameter of interest, and that at the time of
etc., and expressed as psi, mv, sec., etc.
initial or periodic validation, the analyzer was operating at the
conditions specified by the manufacturer and consistently with 3.1.3 analyzer result, n—numerical estimate of a physical,
chemical, or quality parameter produced by applying the
the primary test method.
calibration model to the analyzer output signal.
1.7 The units of measure used in this practice shall be the
3.1.4 bias, n—the difference between the expectation of the
same as those applicable to the test primary method used for
results and an accepted reference value.
analyzer validation.
3.1.5 control sample, n—material similar to the process
1.8 This standard does not purport to address all of the
stream that is stable over long periods of time so that its
safety concerns, if any, associated with its use. It is the
parametersmaybemeasuredreproduciblyinperformancetests
responsibility of the user of this standard to establish appro-
to characterize analyzer precision and accuracy.
3.1.5.1 Discussion—May be a pure compound, standard
This practice is under the jurisdiction of ASTM Committee D16 on Aromatic
mixture, or a sample from the process stream. Its parameters
Hydrocarbons and Related Chemicals and is the direct responsibility of Subcom-
mittee D16.04 on Instrumental Analysis.
Current edition approved June 1, 2012. Published August 2012. Originally
ε1
approved in 2000. Last previous edition approved in 2006 as D6621–00 (2006) . For referenced ASTM standards, visit the ASTM website, www.astm.org, or
DOI: 10.1520/D6621-00R12. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Standards volume information, refer to the standard’s Document Summary page on
this practice. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6621 − 00 (2012)
are used to plot statistical process control charts to define 4. Summary of Practice
analyzer precision in normal operation.
4.1 This practice standardizes aromatic hydrocarbon
process-analyzer performance testing practices, or processes
3.1.6 external performance testing, n—procedure involving
complete substitution of the process/product stream measured formaintainingaccurateandpreciseanalyzermeasurements.It
is used with methods for the measurement and certification of
by the analyzer with a control sample stream to measure the
analyzer’s precision and possibly accuracy (if the control aromatic hydrocarbon materials applied to continuous on-line
analyzers. These methods are generally under the control of
sample’s true value is known).
Committee D16 on Aromatic Hydrocarbons and Related
3.1.7 internal performance testing, n—procedure involving
Chemicals. It is meant as a practical guide for persons setting
the addition of a known quantity of a standard material
up and maintaining these analyzers in a process (non-
homogeneously into the process/product stream measured by
laboratory) environment. They should apply it, with their
the analyzer to measure the analyzer’s precision and possibly
knowledge of the analyzer’s operation and of how the process
accuracy (if the sample material’s true value is known).
analyzer results are to be used, to maintain and optimize
3.1.8 linearity, n—parameter ranges where the analyzer’s
analyzer operation.
results do and do not approximate a straight line.
5. Significance and Use
3.1.9 performance testing of an analyzer, n—mechanical
and statistical procedure for routinely checking the accuracy 5.1 Performance testing of on-line analyzers is critical to
and precision of an analyzer’s results against historical accu- their proper performance within predictable levels of precision
racy and precision for a control sample. andaccuracy.Thispracticecanaffectproductionefficiencyand
certification of aromatic hydrocarbon materials.
3.1.10 precision, n—closeness of agreement of independent
testresultsofthesamechemicalorphysicalpropertyofagiven
6. System Components
material obtained under stipulated conditions.
6.1 Process analyzers for measuring the chemical composi-
3.1.10.1 Discussion—Expressed in terms of dispersion of
tion of aromatic hydrocarbons, their purity, or physical prop-
test results around the arithmetic mean, usually as variance,
erties often replace existing laboratory test methods, using the
standard deviation, repeatability or reproducibility, or both.
same or similar chemical measurement techniques. Fig. 1
3.1.11 repeatability of an analyzer, n—difference between
shows several possible analyzer configurations for on-line
two successive analyzer results measured in a short time
process testing of aromatic hydrocarbon materials. Aromatic
interval that would be exceeded in the long run in only 1 case
hydrocarbon stream analyzers are often based on
in 20 (5% of the time) when the analyzer is operated on a
chromatography, but they may also perform physical
flowing sample of uniform quality.
measurements, wet chemistry, or other methods described in
new or existing Committee D16 methods. This practice is
3.1.12 reproducibility of an analyzer, n—differencebetween
intended to be generally applicable to any of them.
asingleresultfromeachoftwoidenticalanalyzersystemsthat
wouldbeexceededinthelongruninonly1casein20(5%of
7. Performance Guidelines Before Calibration
the time) when the two systems are operated at different sites
by different operators, but on identical samples.
7.1 At startup, validate any process analyzer against an
existing analytical method, typically in this case, one overseen
3.1.13 rule violation, n—condition when a point value or
by Committee D16.
pattern of points in a statistical process control chart statisti-
cally exceeds the defined probability of its occurrence, as 7.2 The capability measurement (c ) for a given analyzer
m
defined by the Western Electric rules (2) being used. (3) shall be less than 0.2, as defined in Eq 1:
2 2
c 5 σ /σ ,0.2 (1)
3.1.14 spot sample, n—representative material resembling
m a p
the stream being monitored, an identical portion of which is
where:
analyzedbothinaprocessanalyzerandbyalaboratoryteston
σ = standard deviation of the analyzer measurement, and
a
a non-scheduled basis for periodic validation testing.
σ = standard deviation of the process.
p
3.1.14.1 Discussion—May be the same material as the
The variance (standard deviation squared) of the analyzer
control sample.
should be less than 20% of the variance of the process, so that
3.1.15 validation of an analyzer, n—process to identify how
the analyzer measurement can be useful for detecting changes
comparableananalyzer’sresultsarestatisticallytoresultsfrom
in the process. The expected capability for a process analyzer
the primary method, or to define how the analyzer’s results
measurement may be available from the vendor for a specific
compare to the primary method’s results in precision and
application before installation of the analyzer (advertised
accuracy.
analyzer capability). Actual process stream measurement ca-
3.1.15.1 Discussion—Must be done when the analyzer is
pability should be measured on the process/product stream,
firstconfiguredorreconfigured(initialvalidation),andthenon
usually after initial analyzer validation.
a periodic basis (periodic validation), as described in Practice
7.3 Automated analyzer sampling practices for aromatic
D3764.
hydrocarbon liquid streams shall follow those referenced in
3.2 For additional definitions, see Appendix X1. Practice D4177.
D6621 − 00 (2012)
FIG. 1 Possible Process Analyzer Configurations
7.4 Determine the linearity of the process analyzer by using analyzed by the process analyzer, and then using statistical
at least three calibration standard materials with known process control (SPC), to define the actual analyzer result’s
compositions/responses for the components of interest. Each precision.
component should be present at a high, low, and medium
8.3 Analyzer performance test frequency can be done at a
concentration/amount level with respect to the concentration/
fixed time interval, based on analyzer reliability and operator
amount range expected for the parameter (analyzer operating
experience.Typically,oncepershift,day,orweekareused,but
range). A plot of the component concentration/amount versus
it may be more or less frequent. Unscheduled control sample
analyzer response will determine if the analyzer has a linear
analyses may be performed whenever the unit operator feels
response over the concentration range of interest. If analyzer
that something has changed in the process or process analyzer,
response is nonlinear, additional calibration standards must be
or at a convenient time.
analyzed to clearly determine the nonlinear behavior of each
8.4 Thecontrolsamplematerialcontainershallbelocatedat
analyzer and component, if the analyzer is to be used in the
a point in the process to allow for its simple and regular
nonlinear range.
introduction into the process analyzer’s sample introduction
7.5 If a process analyzer is to be used only for trend
system (if appropriate) by the process operator. A sufficient
information, the data generated by it is in a form that does not
quantity must be available for many repetitive analyses.
impart compositional information, but relative information
8.5 Perform an external analyzer performance test by
only, that is, peak area, peak height, counts, millivolts, etc.
switching the analyzer sample source from the process stream
Initial validation and frequent performance testing are still
tothecontrolsample,followedbysamplingandanalysisofthe
required to define precision, as well as to maintain proper
control sample.
analyzer operation.
8.6 Monitor the analyzer’s output from the control sample
8. Performance Test Procedure
until it stabilizes, that is, the difference between successive
8.1 Determine analyzer performance using external check readingsisatorbelowtherepeatabilityoftheanalyzer,(which
is measured as described in 8.10). If this does not occur, the
samples, which are substituted for the process material stream
during performance test runs. repeatability of the analyzer has changed and should be
remeasured.
8.2 Process analyzers are routinely performance tested by
using control samples. These may be primary or secondary 8.7 Afterstabilizationoftheanalyzer,measureatleastthree
standard materials, or actual portions from the process stream. successive results on the control sample and average the
These portions must be representative of normal process results. Plot the average of these three results in a SPC chart
conditions, and be stored to remain physically and chemically using any statistically correct method of data handling and
stable over time. The control sample should be repeatedly control chart construction (4).
D6621 − 00 (2012)
8.8 SPC charts of the control sample data shall be used to 8.11 Perform periodic analyzer validation on a scheduled
help decide if the analyzer needs to have its response param- basisoveralongertime(forexample,weeklyormonthly)than
eters reset, (5) or if it is working within previous statistical performance testing, or whenever some significant aspect of
levels and should be left alone. SPC results and operator the analyzer has changed (see Table 1). This activity reestab-
experience should be used to determine subsequent actions, lishes the analyzer’s statistical performance with the primary
such as determining the cause for any rule violation and method.
correcting it.
9. Analyzer Parameter Adjustment
8.9 SPC charts of control samples help the operator to
9.1 Adjust analyzer response parameters only when the
differentiate between normal (random) and abnormal (nonran-
analyzer’scontrolsampleSPCchartindicatesoneormorerule
dom) analyzer variation due to changes in analyzer operation.
violations, and after investigation, causes have been found and
8.9.1 Charts may be maintained manually or with commer-
eliminated.Then, if in the opinion of the operator the r
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