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Product Certification Using Tank Quality Integration (TQI). Nigel Fleming, Esso Petroleum and Jonathan Love, Newcastle University APACT 03, April 2003. Contents. Definitions What is TQI? What is Give-away? The Problem Systematic Give-away. The Solution TQI Certification.

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product certification using tank quality integration tqi

Product Certification Using Tank Quality Integration (TQI)

Nigel Fleming, Esso Petroleum

and Jonathan Love, Newcastle University

APACT 03, April 2003

contents
Contents
  • Definitions
    • What is TQI?
    • What is Give-away?
  • The Problem
    • Systematic Give-away.
  • The Solution
    • TQI Certification.
  • Justification for Change
    • Statistical Precision comparison between TQI and existing method.
slide3

Every 6 minutes

q

q

v

Online analyser

Product

  • Applied recursively:

What is TQI?

  • TQI calculates product tank qualities as the tanks fill, e.g. density, sulphur, cetane, octane ....
what is give away
What is Give-away?
  • A laboratory test method is used to certify the tank quality. (ISO test methods.)
  • Give-away is the difference between the quality you release product at to the customer and the legitimate manufacturing limit.
  • It reduces profit because it debits yield and/or adds to the cost of manufacture.
  • The purpose of this talk is to explain a way of using TQI to reduce give-away.
systematic give away
Systematic Give-away
  • Realized that there was a limit to how small give-away could be reduced.
  • Right First Time (RFT). Due to the rate of product demanded and the no. of tanks per product grade a target of RFT  95% is set.
  • Even if the TQI result is an unbiased estimate of the quality it is still subject to random errors.
    • Error distribution characterized by a variance 2TQI.
  • The Laboratory methods used to test and certify the product quality are subject to random errors.
    • Error distribution characterized by a variance 2ISO.
  • Since TQI is used to manufacture and the Lab. to certify, the delta is important.
    • QD = QT - QL
  • Since the TQI and Lab. results are independent their variances add.
    • 2 = 2TQI + 2ISO
slide6

ISO

Giveaway

ISO

ISO

5% Max.

52 51 50 49 48

Lab Cetane

52 51 50 49 48

Lab Cetane

systematic give away1
Systematic Give-away
  • To ensure RFT 95%,
    • Give-away  = 1.645 
  • This acts as a manufacturing margin which adds a significant additional cost.
    • TQI quality target = min. specification + 1.645 
tqi certification
TQI Certification
  • Alternatively, why not certify TQI for release and remove the manufacturing margin?
    • The risk of litigation if a customer questions a fuel quality.
    • TQI is a complex system relative to, taking a sample in a pint bottle to the lab.
  • Two enabling conditions were set, as follows.
    • Is a TQI result an accurate estimate of the true quality; i.e. an unbiased estimate of the mean?
    • Does a TQI result have a smaller error than a single result using the reference ISO lab. method, i.e. TQI < ISO?
iso test method precision
ISO Test Method Precision?
  • Test methods quote Repeatability and Reproducibility values.
  • Repeatability applies to a sample multi-tested in the same lab. (2r)
  • Reproducibility applies to a sample multi-tested in different labs. (2R)
    • 2R > 2r
  • For the method, 2ISO = 2r + 2R
what is tqi precision
What is TQI Precision?
  • The online analyser accuracy and precision provide the basis for assessing the accuracy and precision of TQI results.
  • Analyser accuracy is set using a validation sample which has been multi-tested in different laboratories.
  • Analyser precision is defined by how much error is introduced by the online analyser.
  • The error in the validation sample and the analyser itself are independent of each other.
    •  2TQI = 2val +
validation sample precision 2 val

2r / M + 2R

Variance (q) = = 2val

N

Validation Sample Precision (2val)?
  • Multi-testing M times in N different labs. using the ISO method generates a sample with a mean qualityq.
    • E(q) = q the true value of the validation sample
  • The validation sample mean is a true estimate of the quality and its precision improves with multi-testing.
analyser precision
Analyser Precision?
  • Another way to look at TQI is as a time series.
analyser precision1
Analyser Precision?
  • Each analyser reading is made up of a deterministic and a stochastic part.

Where at is the true quality

t is a random measurement error

  • Given that variance(t) = 2anl, it can be shown:
  • n is typically between 100 - 200, which significantly reduces the effect of analyser error on the TQI result.
tqi precision defined
TQI Precision Defined
  • Then TQI Precision can be determined from equation (1).
  • For example, for sulphur2TQI = 5.4, 2ISO = 10.5
  • TQI < Ref