ASTM D6621-00

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation: D 6621 – 00
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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope D3764 Practice for Validation of Process Stream Analyz-
ers
1.1 This practice serves as a practical guide for the perfor-
D4177 Practice for Automatic Sampling of Petroleum and
mance testing of process stream analyzers specifically for
Petroleum Products
measuring chemical or physical characteristics of liquid aro-
D6122 Practice for Validation of Multivariate Process In-
matic hydrocarbon materials for production or certification of
frared Spectrophotometers
these materials. The practice may be applicable to other
E456 Terminology Relating to Quality and Statistics
hydrocarbon stream analyzers as well.
E1655 Practices for Infrared, Multivariate, Quantitative
1.2 Only external methods (complete substitution of the
Analysis
process stream with a standard) of control sample introduction
are included. Internal methods are beyond the scope of this
3. Terminology
practice.
3.1 Definitions:
1.3 Methods for resetting key operational parameters of
3.1.1 accuracy—closeness of agreement between a test
analyzers to match predefined limits are provided by vendors
result and an accepted reference value.
and are not included in this practice.
3.1.2 analyzer output—signal that is proportional to the
1.4 Analyzer validation procedures are covered in Practices
quality parameter being measured and suitable for input to
D3764 and D6122, not in this practice.
readout instrumentation.
1.5 Procedures for statistically interpreting data from auto-
3.1.2.1 Discussion—Itmaybepneumatic,electrical,digital,
matic sampling process stream analyzers are outlined.
etc., and expressed as psi, mv, sec., etc.
1.6 The implementation of this practice requires that the
3.1.3 analyzer result—numerical estimate of a physical,
analyzer be installed according to APIRP-550 (1) , and be in
chemical, or quality parameter produced by applying the
agreement with the analyzer supplier’s recommendations.
calibration model to the analyzer output signal.
Also, it assumes that the analyzer is designed to monitor the
3.1.4 bias—the difference between the expectation of the
specific material parameter of interest, and that at the time of
results and an accepted reference value.
initial or periodic validation, the analyzer was operating at the
3.1.5 control sample—materialsimilartotheprocessstream
conditions specified by the manufacturer and consistently with
that is stable over long periods of time so that its parameters
the primary test method.
may be measured reproducibly in performance tests to charac-
1.7 The units of measure used in this practice shall be the
terize analyzer precision and accuracy.
same as those applicable to the test primary method used for
3.1.5.1 Discussion—May be a pure compound, standard
analyzer validation.
mixture, or a sample from the process stream. Its parameters
1.8 This standard does not purport to address all of the
are used to plot statistical process control charts to define
safety concerns, if any, associated with its use. It is the
analyzer precision in normal operation.
responsibility of the user of this standard to establish appro-
3.1.6 external performance testing—procedure involving
priate safety and health practices, and determine the applica-
complete substitution of the process/product stream measured
bility of regulatory limitations prior to use.
by the analyzer with a control sample stream to measure the
2. Referenced Documents analyzer’s precision and possibly accuracy (if the control
sample’s true value is known).
2.1 ASTM Standards:
This practice is under the jurisdiction of ASTM Committee D16 on Aromatic
Hydrocarbons and Related Chemicals and is the direct responsibility of Subcom-
mittee D16.09 on On-Line Analysis. Annual Book of ASTM Standards, Vol. 5.02.
Current edition approved Dec. 10, 2000. Published February 2001. Annual Book of ASTM Standards, Vol. 5.04.
2 5
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof Annual Book of ASTM Standards, Vol. 14.02.
this practice. Annual Book of ASTM Standards, Vol. 3.06.
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D6621–00
3.1.7 internal performance testing—procedure involving knowledge of the analyzer’s operation and of how the process
the addition of a known quantity of a standard material analyzer results are to be used, to maintain and optimize
homogeneously into the process/product stream measured by analyzer operation.
the analyzer to measure the analyzer’s precision and possibly
5. Significance and Use
accuracy (if the sample material’s true value is known).
5.1 Performance testing of on-line analyzers is critical to
3.1.8 linearity—parameter ranges where the analyzer’s re-
sults do and do not approximate a straight line. their proper performance within predictable levels of precision
andaccuracy.Thispracticecanaffectproductionefficiencyand
3.1.9 performance testing of an analyzer—mechanical and
statistical procedure for routinely checking the accuracy and certification of aromatic hydrocarbon materials.
precision of an analyzer’s results against historical accuracy
6. System Components
and precision for a control sample.
6.1 Process analyzers for measuring the chemical composi-
3.1.10 precision—closeness of agreement of independent
tion of aromatic hydrocarbons, their purity, or physical prop-
testresultsofthesamechemicalorphysicalpropertyofagiven
erties often replace existing laboratory test methods, using the
material obtained under stipulated conditions.
same or similar chemical measurement techniques. Fig. 1
3.1.10.1 Discussion—Expressed in terms of dispersion of
shows several possible analyzer configurations for on-line
test results around the arithmetic mean, usually as variance,
process testing of aromatic hydrocarbon materials. Aromatic
standard deviation, repeatability or reproducibility, or both.
hydrocarbon stream analyzers are often based on chromatog-
3.1.11 repeatability of an analyzer—differencebetweentwo
raphy, but they may also perform physical measurements, wet
successive analyzer results measured in a short time interval
chemistry, or other methods described in new or existing
that would be exceeded in the long run in only 1 case in 20
Committee D16 methods. This practice is intended to be
(5% of the time) when the analyzer is operated on a flowing
generally applicable to any of them.
sample of uniform quality.
3.1.12 reproducibility of an analyzer—difference between a
7. Performance Guidelines Before Calibration
single result from each of two identical analyzer systems that
7.1 At startup, validate any process analyzer against an
wouldbeexceededinthelongruninonly1casein20(5%of
existing analytical method, typically in this case, one overseen
the time) when the two systems are operated at different sites
by Committee D16.
by different operators, but on identical samples.
7.2 The capability measurement (c ) for a given analyzer
3.1.13 rule violation—condition when a point value or
m
(3) shall be less than 0.2, as defined in Eq 1:
pattern of points in a statistical process control chart statisti-
cally exceeds the defined probability of its occurrence, as 2 2
c 5s / s <0.2 (1)
m a p
defined by the Western Electric rules (2) being used.
where:
3.1.14 spot sample—representative material resembling the
s = standard deviation of the analyzer measurement, and
stream being monitored, an identical portion of which is a
s = standard deviation of the process.
analyzed both in a process analyzer and by a laboratory test on p
The variance (standard deviation squared) of the analyzer
a non-scheduled basis for periodic validation testing.
should be less than 20% of the variance of the process, so that
3.1.14.1 Discussion—May be the same material as the
the analyzer measurement can be useful for detecting changes
control sample.
in the process. The expected capability for a process analyzer
3.1.15 validation of an analyzer—process to identify how
measurement may be available from the vendor for a specific
comparableananalyzer’sresultsarestatisticallytoresultsfrom
application before installation of the analyzer (advertised
the primary method, or to define how the analyzer’s results
analyzer capability). Actual process stream measurement ca-
compare to the primary method’s results in precision and
pability should be measured on the process/product stream,
accuracy.
usually after initial analyzer validation.
3.1.15.1 Discussion—Must be done when the analyzer is
7.3 Automated analyzer sampling practices for aromatic
firstconfiguredorreconfigured(initialvalidation),andthenon
hydrocarbon liquid streams shall follow those referenced in
a periodic basis (periodic validation), as described in Practice
Practice D4177.
D3764.
7.4 Determine the linearity of the process analyzer by using
3.2 For additional definitions, see Appendix X1.
at least three calibration standard materials with known
4. Summary of Practice
compositions/responses for the components of interest. Each
4.1 This practice standardizes aromatic hydrocarbon component should be present at a high, low, and medium
process-analyzer performance testing practices, or processes concentration/amount level with respect to the concentration/
formaintainingaccurateandpreciseanalyzermeasurements.It amount range expected for the parameter (analyzer operating
is used with methods for the measurement and certification of range). A plot of the component concentration/amount versus
aromatic hydrocarbon materials applied to continuous on-line analyzer response will determine if the analyzer has a linear
analyzers. These methods are generally under the control of response over the concentration range of interest. If analyzer
Committee D16 on Aromatic Hydrocarbons and Related response is nonlinear, additional calibration standards must be
Chemicals. It is meant as a practical guide for persons setting analyzed to clearly determine the nonlinear behavior of each
up and maintaining these analyzers in a process (non- analyzer and component, if the analyzer is to be used in the
laboratory) environment. They should apply it, with their nonlinear range.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D6621–00
FIG. 1 Possible Process Analyzer Configurations
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D6621–00
7.5 If a process analyzer is to be used only for trend 8.9.1 Charts may be maintained manually or with commer-
information, the data generated by it is in a form that does not cially available SPC software, preferably as part of the ana-
impart compositional information, but relative information lyzer data acquisition and control software.
only, that is, peak area, peak height, counts, millivolts, etc.
8.9.2 Control limits should be set at three (3) sigma (stan-
Initial validation and frequent performance testing are still
darddeviations)fromthemeanvalue,warninglimitsattwo(2)
required to define precision, as well as to maintain proper
sigma, and suitable Western Electric rules (2) invoked, consis-
analyzer operation.
tent with plant/facility statistical policy.
8.9.3 Allruleviolationsshallbeinvestigatedandeliminated
8. Performance Test Procedure
if possible, with all causes and actions documented with the
charts.
8.1 Determine analyzer performance using external check
samples, which are substituted for the process material stream 8.9.4 If a cause cannot be determined, analyzer operation
should continue without any parameter adjustment until the
during performance test runs.
next performance test.
8.2 Process analyzers are routinely performance tested by
using control samples. These may be primary or secondary
8.9.5 If there are no rule violations, analyzer parameter
standard materials, or actual portions from the process stream. adjustment is not needed.
These portions must be representative of normal process
8.9.6 If a rule violation’s cause is determined and elimi-
conditions, and be stored to remain physically and chemically
nated,andiftheoperatorfeelsthattheanalyzer’saccuracyhas
stable over time. The control sample should be repeatedly
changed as a result, proceed to reset analyzer parameters, as
analyzed by the process analyzer, and then using statistical
discussed in Section 9. If precision needs to be redefined for
process control (SPC), to define the actual analyzer result’s
the analysis process, follow the procedure listed in 8.10.
precision.
8.10 To determine the repeatability of the analyzer, follow
8.3 Analyzer performance test frequency can be done at a
the following procedure:
fixed time interval, based on analyzer reliability and operator
8.10.1 Switch a control sample into the analyzer and wait
experience.Typically,oncepershift,day,orweekareused,but
for stabilization as discussed in 8.6.
it may be more or less frequent. Unscheduled control sample
8.10.2 Measure at least eleven (6) successive analyses on
analyses may be performed whenever the unit operator feels
the control sample over at least1hor reasonable interval on
that something has changed in the process or process analyzer,
the same day. The control sample should be switched into and
or at a convenient time.
out of the analyzer stream for each determination.
8.4 Thecontrolsamplematerialcontainershallbelocatedat
8.10.3 The 95% repeatability limit of the measurement for
a point in the process to allow for its simple and regular
the analyzer equals the standard deviation of these 11 succes-
introduction into the process analyzer’s sample introduction
sive runs multiplied by 2.8, in accordance with Terminology
system (if appropriate) by the process operator. A sufficient
E456.
quantity must be available for many repetitive analyses.
8.10.4 Recalculate the analyzer’s control limits based on
8.5 Perform an external analyzer performance test by
this new set of data
...