EN ISO 4259-2:2017
(Main)Petroleum and related products - Precision of measurement methods and results - Part 2: Interpretation and application of precision data in relation to methods of test (ISO 4259-2:2017)
Petroleum and related products - Precision of measurement methods and results - Part 2: Interpretation and application of precision data in relation to methods of test (ISO 4259-2:2017)
ISO 4259-2:2017 specifies the methodology for the application of precision estimates of a test method derived from ISO 4259‑1. In particular, it defines the procedures for setting the property specification limits based upon test method precision where the property is determined using a specific test method, and in determining the specification conformance status when there are conflicting results between supplier and receiver. Other applications of this test method precision are briefly described in principle without the associated procedures.
The procedures in ISO 4259-2:2017 have been designed specifically for petroleum and petroleum-related products, which are normally homogeneous. However, the procedures described in ISO 4259-2:2017 can also be applied to other types of homogeneous products. Careful investigations are necessary before applying ISO 4259-2:2017 to products for which the assumption of homogeneity can be questioned.
Mineralölerzeugnisse - Präzision von Messverfahren und Ergebnissen - Teil 2: Anwendung der Präzisionsdaten von Prüfverfahren (ISO 4259-2:2017)
Produits pétroliers et connexes - Fidélité des méthodes de mesure et de leurs résultats - Partie 2: Application des valeurs de fidélité relatives aux méthodes d'essai (ISO 4259-2:2017)
Le présent document prescrit la méthodologie pour l'application des estimations de fidélité d'une méthode d'essai déterminée selon l'ISO 4259‑1. En particulier, il définit les procédures à suivre pour fixer les limites de spécification d'une caractéristique sur la base de la fidélité de la méthode d'essai qui permet de déterminer la caractéristique en utilisant une méthode d'essai spécifique et pour déterminer l'état de conformité à une spécification quand il y a des résultats contradictoires entre le fournisseur et le destinataire. D'autres applications de cette fidélité des méthodes d'essai sont brièvement décrites en principe sans les procédures associées.
Les procédures du présent document ont été conçues spécifiquement pour les produits pétroliers et leurs produits connexes qui sont normalement homogènes. Les procédures décrites dans le présent document peuvent cependant aussi s'appliquer à d'autres types de produits homogènes. Il est nécessaire de procéder à des contrôles attentifs avant d'appliquer le présent document à des produits pour lesquels la présomption d'homogénéité peut être mise en question.
Nafta in sorodni proizvodi - Natančnost merilnih metod in rezultatov - 2. del: Razlaga in uporaba podatkov o natančnosti preskusnih metod (ISO 4259-2:2017)
Ta dokument določa metodologijo za uporabo ocen natančnosti preskusne metode iz standarda ISO 4259-1. Določa predvsem postopke za določitev omejitev specifikacij lastnosti na podlagi natančnosti preskusne metode, če se lastnost določi z uporabo posebne preskusne metode,
in pri določanju statusa skladnosti specifikacije, če med dobaviteljem in prejemnikom obstajajo nasprotujoči si rezultati. Drugi načini uporabe natančnosti te preskusne metode so na kratko opisani brez povezanih postopkov.
Postopki v tem dokumentu so bili zasnovani posebej za nafto in sorodne proizvode, ki so običajno homogeni. Kljub temu se postopki, opisani v tem dokumentu, lahko uporabljajo pri drugih vrstah homogenih proizvodov. Pred uporabo tega dokumenta za proizvode, pri katerih je predpostavka o homogenosti lahko vprašljiva, so potrebne temeljite preiskave.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-februar-2018
1DGRPHãþD
SIST EN ISO 4259:2006
1DIWDLQVRURGQLSURL]YRGL1DWDQþQRVWPHULOQLKPHWRGLQUH]XOWDWRYGHO
5D]ODJDLQXSRUDEDSRGDWNRYRQDWDQþQRVWLSUHVNXVQLKPHWRG ,62
Petroleum and related products - Precision of measurement methods and results - Part
2: Interpretation and application of precision data in relation to methods of test(ISO 4259-
2:2017)
Mineralölerzeugnisse - Präzision von Messverfahren und Ergebnissen - Teil 2:
Anwendung der Werte für die Präzision von Prüfverfahren (ISO 4259-2:2017)
Produits pétroliers - Fidélité des méthodes de mesure et des résultats - Partie 2:
Application des valeurs de fidélité relatives aux méthodes d'essai (ISO 4259-2:2017)
Ta slovenski standard je istoveten z: EN ISO 4259-2:2017
ICS:
75.080 Naftni proizvodi na splošno Petroleum products in
general
75.180.30 Oprema za merjenje Volumetric equipment and
prostornine in merjenje measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 4259-2
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2017
EUROPÄISCHE NORM
ICS 75.080 Supersedes EN ISO 4259:2006
English Version
Petroleum and related products - Precision of
measurement methods and results - Part 2: Interpretation
and application of precision data in relation to methods of
test (ISO 4259-2:2017)
Produits pétroliers - Fidélité des méthodes de mesure Mineralölerzeugnisse - Präzision von Messverfahren
et des résultats - Partie 2: Application des valeurs de und Ergebnissen - Teil 2: Anwendung der Werte für die
fidélité relatives aux méthodes d'essai (ISO 4259- Präzision von Prüfverfahren (ISO 4259-2:2017)
2:2017)
This European Standard was approved by CEN on 27 October 2017.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 4259-2:2017 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 4259-2:2017) has been prepared by Technical Committee ISO/TC 28
"Petroleum and related products, fuels and lubricants from natural or synthetic sources" in
collaboration with Technical Committee CEN/TC 19 “Gaseous and liquid fuels, lubricants and related
products of petroleum, synthetic and biological origin” the secretariat of which is held by NEN.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2018, and conflicting national standards shall be
withdrawn at the latest by June 2018.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 4259:2006.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 4259-2:2017 has been approved by CEN as EN ISO 4259-2:2017 without any
modification.
INTERNATIONAL ISO
STANDARD 4259-2
First edition
2017-11
Petroleum and related products —
Precision of measurement methods
and results —
Part 2:
Interpretation and application of
precision data in relation to methods
of test
Produits pétroliers — Fidélité des méthodes de mesure et des
résultats —
Partie 2: Application des valeurs de fidélité relatives aux méthodes
d'essai
Reference number
ISO 4259-2:2017(E)
©
ISO 2017
ISO 4259-2:2017(E)
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved
ISO 4259-2:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Application and significance of repeatability, r, and reproducibility, R .2
4.1 General . 2
4.2 Repeatability, r . 2
4.2.1 General. 2
4.2.2 Acceptability of results . 2
4.2.3 Confidence limits calculations using results collected under
repeatability conditions. 3
4.3 Reproducibility, R . 3
4.3.1 Acceptability of results . 3
4.3.2 Confidence limits calculations using results collected under
reproducibility conditions . 5
4.4 Use of reproducibility to determine bias between two different test methods that
purport to measure the same property . 5
4.4.1 General. 5
4.4.2 Process . 5
5 Specifications . 6
5.1 Aim of specifications . 6
5.2 Construction of specifications limits in relation to scope and precision of the
specified test method . 6
6 Assessment of quality conformance to specification . 7
6.1 General . 7
6.2 Assessment of quality conformance by the supplier . 8
6.3 Assessment of quality conformance by the recipient . 9
6.3.1 General. 9
6.3.2 Single batch of product . 9
6.3.3 Multiple batches of product . 9
6.3.4 Procedure for recipient to assess conformance for a single batch of product.10
7 Dispute procedure .11
7.1 Resolve dispute by negotiation .11
7.2 Use of the test method or procedure in case of dispute .11
7.3 Dispute resolution procedure .12
7.4 Dispute unresolved.12
7.5 Example of a dispute resolution.14
Annex A (informative) Explanation of formulae given in Clause 4 .15
Annex B (informative) Dispute resolution for specifications based on a specified degree
of criticality .18
Annex C (informative) Statistical control in the execution of test methods by a laboratory.21
Annex D (informative) General approach to bias assessment using multiple materials .23
Annex E (informative) Glossary .24
Bibliography .25
ISO 4259-2:2017(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 28, Petroleum and related products, fuels
and lubricants from natural or synthetic sources.
This first edition of ISO 4259-2, together with ISO 4259-1, cancels and replaces ISO 4259, which has
been technically revised. This document provides the content of Clauses 7 to 10 of ISO 4259 and
connected Annexes H and I. The remaining Clauses and Annexes A to G of ISO 4259:2006 are replaced
by ISO 4259-1.
A list of all parts in the ISO 4259 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved
ISO 4259-2:2017(E)
Introduction
For purposes of setting product specifications, and to check product compliance against these
specifications, standard test methods are usually referenced for specific properties of commercial
petroleum and related products. Two or more measurements of the same property of a specific sample
by a specific test method, or by different test methods that purport to measure the same property,
will not usually give exactly the same result. It is, therefore, necessary to take proper account of this
fact when setting product specifications, assessing if the differences between test results are within
statistical expectation, and making specification compliance decisions based on limited test results.
By using statistically-based estimates of the precision for a test method, the following can be achieved:
— an objective measure of the reliability of specification limits,
— a specification compliance decision, and
— the degree of agreement expected between two or more results obtained in specified circumstances.
This document describes the applications of the precision of test method as derived from ISO 4259-1. It is
intended to be a companion document to ISO 4259-1. Additional normative and informative discussions
on how to use this precision to assess the “in statistical control” status and precision capability of a
specific laboratory in the execution of a test method are provided. Also, the general approach to the
agreement between two different test methods that purport to measure the same property are given.
The two parts of ISO 4259 encompass both the determination of precision estimates and the application
[1]
of precision data. It attempts to be aligned with ASTM D6300 regarding the determination of the
[2]
precision estimates and with ASTM D3244 for the utilization of test data.
A glossary of the variables used in this document and ISO 4259-1 is included in ISO 4259-1:2017, Annex I.
INTERNATIONAL STANDARD ISO 4259-2:2017(E)
Petroleum and related products — Precision of
measurement methods and results —
Part 2:
Interpretation and application of precision data in relation
to methods of test
1 Scope
This document specifies the methodology for the application of precision estimates of a test method
derived from ISO 4259-1. In particular, it defines the procedures for setting the property specification
limits based upon test method precision where the property is determined using a specific test method,
and in determining the specification conformance status when there are conflicting results between
supplier and receiver. Other applications of this test method precision are briefly described in principle
without the associated procedures.
The procedures in this document have been designed specifically for petroleum and petroleum-related
products, which are normally homogeneous. However, the procedures described in this document can
also be applied to other types of homogeneous products. Careful investigations are necessary before
applying this document to products for which the assumption of homogeneity can be questioned.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 4259-1, Petroleum and related products — Precision of measurement methods and results — Part 1:
Determination of precision data in relation to methods of test
3 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 4259-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
proficiency testing program
PTP
program designed for the periodic evaluation of participating laboratories’ testing capability of a
Standard Test Method through the statistical analysis of their test results obtained on aliquots prepared
from a single batch of homogeneous material
Note 1 to entry: The frequency of such testing varies in accordance with the program objective. Each execution of
testing involves testing of a single batch of material. Materials typically vary from test to test.
Note 2 to entry: This is also commonly referred to as Inter Laboratory Cross Check Program (ILCP).
ISO 4259-2:2017(E)
3.2
recipient
individual or organization who receives or accepts a product delivered by the supplier
3.3
supplier
individual or organization responsible for the quality of a product just before it is taken over by the
recipient
4 Application and significance of repeatability, r, and reproducibility, R
4.1 General
The value of these quantities is estimated from analysis of variance (two-factor with replication)
performed on the results obtained in a statistically designed inter-laboratory programme in
which different laboratories each test a range of samples. Repeatability and reproducibility values
estimated in accordance with ISO 4259-1 or other statistical techniques shall be included in each
published test method.
NOTE See Annex A for an account of the statistical reasoning underlying the formulae in this clause.
In the following clauses, it is assumed that the result(s) are obtained from a test method that is in
statistical control. For determination of “in statistical control”, see Annex C.
4.2 Repeatability, r
4.2.1 General
Most laboratories do not carry out more than one test on each sample for routine quality control
purposes except in some circumstances, such as in cases of dispute or if the test operator wishes to
confirm that his technique is satisfactory. In such circumstances, when multiple results are obtained,
it is useful to check the consistency of repeated results against the repeatability of the method. The
appropriate procedure is outlined in 4.2.2. It is also useful to know what degree of confidence may be
placed on the average results, and the method of determining this is given in 4.2.3.
4.2.2 Acceptability of results
When only two results are obtained under repeatability conditions and their difference is less than or
equal to r, the test operator may consider his work as being under control and may take the average of
the two results as the estimated value of the property being tested.
If the two results differ by more than r, both shall be considered as suspect and at least three more
results obtained. Including the first two, the difference between the most divergent result and the
average of the remainder shall then be calculated and this difference compared with a new value, r ,
instead of r, given in Formula (1):
k
rr = (1)
21()k−
where k is the total number of results obtained.
If the difference is less than or equal to r , all the results shall be accepted. If the difference exceeds r ,
1 1
the most divergent result shall be rejected and the procedure specified in this section repeated until an
acceptable set of results is obtained.
The average of the acceptable results shall be taken as the estimated value of the property. However, if
two or more results from a total of not more than 20 have been rejected, the operating procedure and
the apparatus shall be checked and a new series of tests made, if possible.
2 © ISO 2017 – All rights reserved
ISO 4259-2:2017(E)
4.2.3 Confidence limits calculations using results collected under repeatability conditions
When a single test operator, who is working within the precision limits of the method, obtains a series
of k results under repeatability conditions, giving an average, X , and the results meet the repeatability
requirement in 4.2.2, it can be assumed with 95 % confidence that the true value, μ, of the characteristic
lies within the following limits:
R R
X − ≤≤μ X + (2)
where
1
R =− 1− (3)
Rr
1
k
When k = 1, use the single test result as the value for the X term as follows:
R R
X − ≤≤μ X + (4)
where R is the published test method reproducibility as discussed in 4.3.
Similarly, for the single limit situation, when only one limit is fixed (upper or lower), it can be assumed
with 95 % confidence that the true value, μ, of the characteristic is limited as follows:
μ ≤+XR05, 9 (upper limit) (5)
()
or
μ ≥−XR05, 9 (lower limit) (6)
()
The factor 0,59 is the ratio 0,84 2 , where 0,84 is derived in Annex A.
When r is much smaller than R, little improvement in the precision of the average is obtained by
carrying out multiple testing under repeatability conditions.
4.3 Reproducibility, R
4.3.1 Acceptability of results
The procedure specified in 4.3 is intended for judging the acceptability, with respect to the
reproducibility of the test method, of results obtained by different laboratories in normal, day-to-day
operations and transactions. In cases of dispute between a supplier and a recipient, the procedure
specified in Clauses 5 to 7 shall be adopted.
When single results are obtained in two laboratories and their difference is less than or equal to R, the
two results shall be considered as acceptable, and used to calculate the average X . The average X ,
rather than either single result separately, shall be used as the estimated value of the tested property.
ISO 4259-2:2017(E)
The true value μ of the characteristic is contained within the following limits with a 95 % confidence:
R R
X − ≤≤μ X + (7)
Similarly for the single limit situation, when only one limit is fixed (upper or lower), the true value μ of
the characteristic is contained with the following limits with a 95 % confidence:
μ ≤+XR04, 2 (upper limit) (8)
()
or
μ ≥−XR04, 2 (lower limit) (9)
()
The factor 0,42 is the ratio of 05, 92 as it is an average of two results.
If the two results differ by more than R, both shall be considered as suspect. Each laboratory shall then
obtain at least three other acceptable results (see 4.2.2).
In this case, the difference between the averages of all acceptable results of each laboratory shall be
judged for conformity using a new value, R , instead of R, as given by Formula (10):
1 1
R =− 1−− (10)
Rr
2kk2
where
R is the reproducibility of the method;
r is the repeatability of the method;
k is the number of results of the first laboratory;
k is the number of results of the second laboratory.
If the difference between the averages is less than or equal to R , then these averages are acceptable and
their overall average shall be considered as the estimated value of the tested property. If the difference
between the averages is greater than R , and there is a dispute on the specification conformance of the
tested property, then the procedure specified in Clause 7 shall be adopted.
If circumstances arise in which there are more than two laboratories, each supplying one or more
acceptable results, the difference between the most divergent laboratory average and the average of
the remaining N laboratory averages shall be compared to R :
where
2 2
R R
1 4
R =+ (11)
22N
11 1
r
R =− N−− −−. (12)
R
4
N
kk k
12 N
R is given in Formula (3), and corresponds to the most divergent laboratory average.
If this difference is equal to or less than R in absolute value, all results shall be regarded as acceptable
and their average taken as the estimated value of the property.
4 © ISO 2017 – All rights reserved
ISO 4259-2:2017(E)
If the difference is greater than R , the most divergent laboratory average shall be rejected and the
comparison using Formulae (11) and (12) repeated until an acceptable set of laboratory averages is
obtained. The average of these laboratory averages shall be taken as the estimated value of the property.
However, if two or more laboratory averages from a total of not more than 20 have been rejected, the
operating procedure and the apparatus shall be checked and a new series of tests made, if possible.
4.3.2 Confidence limits calculations using results collected under reproducibility conditions
When N laboratories obtain one or more results under conditions of repeatability and reproducibility,
giving an average of laboratory averages X , the true value μ of the characteristic is contained within
the following limits with 95 % confidence:
R R
X−≤μ≤+X (13)
22N N
Similarly for the single limit situation, when only one limit is fixed (upper or lower), the true value μ of
the characteristic is contained with the following limits with 95 % confidence:
R
μ ≤+X 05, 9 (upper limit) (14)
N
or
R
μ ≥−X 05, 9 (lower limit) (15)
N
4.4 Use of reproducibility to determine bias between two different test methods that
purport to measure the same property
4.4.1 General
For the situation where two different test methods purport to measure the same property, the
reproducibility estimates (R) from the respective test methods shall be used in conjunction with the
averages obtained from multiple laboratories for the same material to determine if a bias correction
can be applied to improve statistically the agreement between the two methods for that material. For
example, results collected through Proficiency Testing Programs (PTP) for different test methods using
the same sample can be analysed in this fashion.
NOTE Discussion on methodology for this type of assessment for the simultaneous analysis of multiple
materials / property levels that span the intersecting scope of two different test methods is beyond the scope of
[3]
this document. Interested readers are encouraged to consult ASTM D6708 for a detailed presentation on the
subject. Annex D provides a brief overview on the general statistical approach for the aforementioned situation.
4.4.2 Process
Assume that Test Method A and Test Method B are test methods that purport to measure property C.
Calculate the following statistic:
||YY−
AB
Z = (16)
R R
A B
+
7,,683L 7 683L
A B
where
ISO 4259-2:2017(E)
Y is the average from L results for property C for a material using Test Method A, where each
A i
result is a single result obtained under reproducibility conditions;
L is the total number of laboratories (results) for Test Method A and should be >20;
A
R is the reproducibility of Test Method A;
A
Y is the average from L results for property A using Test Method B on the same material tested
B B
by Test Method A, where each result is a single result obtained under reproducibility conditions;
L is the total number of laboratories (results) for Test Method B, and should be >20;
B
R is the reproducibility of Test Method B.
B
If Z > 2, it shall be concluded, with 95 % confidence, that a constant bias correction statistically improves
the degree of agreement between Test Method 1 and Test Method 2 for property C for this material.
5 Specifications
5.1 Aim of specifications
The purpose of a specification is to specify an acceptable limit or limits to the true value, μ, of the
property as determined by a specified test method. In practice, however, this true value can never
be established exactly since the results obtained by applying the specified test method in a single or
multiple laboratories can show acceptable scattering as defined by the repeatability and reproducibility.
There is, therefore, always some uncertainty as to the true value of the tested property determined
from a finite number of test results.
Petroleum product compliance with specifications is assessed in accordance with Clauses 6 and 7. By
prior agreement a supplier and recipient may use the alternative procedures described in Annex B.
It is important that the test method specified for the determination of the property governed by the
specification limit(s) is sufficiently precise to reliably determine whether or not the product meets the
specifications.
5.2 Construction of specifications limits in relation to scope and precision of the
specified test method
The specification limits shall not be outside the method scope limits as determined in ISO 4259-1.
The lower specification limit shall not be less than the lower scope limit of the test method, and the
upper specification limit shall not be greater than the upper scope limit of the test method (see §6.5 in
ISO 4259-1).
In addition, the distance between lower and upper specification limit shall also satisfy the following
condition: upper specification limit minus lower specification limit shall not be less than the quantity
2R evaluated at lower method scope limit plus 2R evaluated at upper method scope limit. See Figure 1
for an illustration of this concept.
Usually, specifications deal with limits for the values of the properties. To avoid uncertainty, such limits
are normally expressed as “not less than” or “not greater than”. Limits are of two types:
— a double limit, upper and lower, for example viscosity not less than 5 mm /s and not greater than
16 mm /s; boiling point 100 °C ± 0,5 °C;
— a single limit, upper or lower, for example water content not greater than 2 %; sulfur content not
greater than 10 mg/kg ; solubility of bitumen not less than 99 %.
6 © ISO 2017 – All rights reserved
ISO 4259-2:2017(E)
Figure 1 — Specification setting
In cases where, for practical reasons, the value of (A − A ) is less than the above minimum range
1 2
requirement in Figure 1, the results obtained will be of doubtful significance in determining whether a
sample does or does not satisfy the requirements of the specification. According to statistical reasoning,
it is desirable for (A − A ) to be considerably greater than the above minimum range requirement. If
1 2
not, one or both of the following courses shall be adopted:
a) the specification limits shall be examined to see whether they can be widened to fit in with the
precision of the test method;
b) the test method shall be examined to see whether the precision can be improved, or an alternative
test method adopted with an improved precision, to fit in with the desired specification limits.
Conformity to this document requires specifications to be drawn up in accordance with the above
principles.
6 Assessment of quality conformance to specification
6.1 General
6.1.1 Clause 6 provides general information to allow the supplier or the recipient to judge the quality
of a product with regard to the specification based on a single test result as obtained by the supplier
or recipient. If both the supplier's and recipient's single test results are available, the estimate of the
true value shall be obtained in accordance with 4.3. Should the recipient decide to dispute the quality
ISO 4259-2:2017(E)
conformance to specification after examining his single result, or the estimate from 4.3, the procedure
specified in Clause 7 shall be adopted.
As a prerequisite for acceptance for laboratory test results to be used in 6.2, 6.3, Clause 7 and Annex B,
the conditions in 6.1.2 to 6.1.4 shall be satisfied.
6.1.2 Each laboratory's test result shall be obtained from a test method that is in statistical control
in terms of precision and bias, as substantiated by in-house SQC charts or other equivalent statistical
techniques.
NOTE For a general discussion on the topic of statistical control and control charts, see Annex C.
6.1.3 The standard deviation from the control charts (or equivalent statistical techniques) in 6.1.2,
as calculated from at least 30 most recent results obtained over at least 15 days, with results that are
separated by at least 6 h, shall not exceed the published test method standard deviation (R / 2,77).
If evidence exists from the published results of multiple PTP, that the R for a published test method is
statistically inconsistent with the R actually achieved, the latter may be used in lieu of the published R
to judge conformance to this clause, provided all of the following conditions are met:
— if legally permissible, and
— if the R calculated from multiple PTP have sufficient degrees of freedom (>30) using results that
have been properly screened for outliers in accordance with GESD protocol in ISO 4259-1 or other
equivalent statistical technique, and
— upon mutual agreement between disputing parties.
6.1.4 Each laboratory shall be able to demonstrate, by way of results from participation in PTPs, if
available, a sustained testing proficiency and a lack of bias relative to PTP averages for the appropriate
test method(s). In the event that a suitable PTP is not available, proficiency shall be demonstrated by
way of testing certified reference materials (CRM) and in-house control charts on quality control (QC)
samples, or by other method validation techniques acceptable to both parties.
6.2 Assessment of quality conformance by the supplier
A supplier who has no other source of information on the true value of a characteristic than a single
result shall consider, with 95 % confidence, that the product meets the specification limit, only if the
result, X , is such that
s
— in the case of a single upper limit, A :
X ≤ A − 0,59R (17)
s 1
— in the case of a single lower limit, A :
X ≥ A + 0,59R (18)
s 2
— in the case of a double limit (A and A ), both these conditions are satisfied (see 4.2.3).
1 2
The 95 % confidence decision limits as calculated using Formulae (17) and (18) are for the guidance of
the supplier, and are not to be interpreted as an obligation. A reported value between the specification
value and the limit from Formula (17) or (18) is not proof of non-compliance, but is an indication that
the confidence for the product to meet the specification limit is less than 95 %. If the result is exactly
at the specification limit, the probability of a re-test result meeting specification, by either the supplier
or the recipient, is 50 %. A direct consequence of releasing product with a low confidence is that the
probability of the receiver obtaining an off-specification result will be high.
8 © ISO 2017 – All rights reserved
ISO 4259-2:2017(E)
The supplier shall only release the product if their test result meets specification or by mutual
agreement with the customer.
If multiple results are obtained by the supplier under repeatability conditions, the average of the
acceptable results and R as determined in 4.2.2 and 4.2.3 shall be used by the supplier as the basis for
determination of specification conformance.
In the event of a dispute with the recipient, procedures in Clause 7 shall be followed.
6.3 Assessment of quality conformance by the recipient
6.3.1 General
Figure 2 is a procedure flowchart that describes steps outlined in this subclause, taking into account all
available data and requirements of this document.
6.3.2 Single batch of product
A recipient who has no other source of information on the true value of a characteristic than a single
result shall consider that the product fails the specification limit with 95 % confidence, only if the
result, x, is such that:
— in the case of an upper limit of the specification A ,
x > A + 0,59R (19)
— in the case of a lower limit of the specification A ,
x < A − 0,59R (20)
— in the case of a double limit (A and A ), either of these conditions applies.
1 2
The 95 % confidence decision limits as calculated using Formulae (19) and (20) is for the guidance of
the recipient, and is not to be interpreted as an obligation. A reported value between the specification
value and the limit from Formula (19) or (20) is not proof of non-conformance, but is an indication that
the confidence for the product failing specification limit is less than 95 %. If the result is exactly at the
specification limit, the probability of a re-test meeting specification, by either the supplier or recipient,
is 50 %.
If multiple results are obtained by the recipient under repeatability conditions, the average of
the acceptable results and R as determined in 4.2.3 shall be used as the basis for determination of
specification conformance.
Should the recipient decide to dispute the specification conformance status for the batch in question,
regardless of the recipient's result that was used as a basis for the decision to dispute, the procedures
in Clause 7 shall be adhered to.
6.3.3 Multiple batches of product
Persistent results over multiple batches that fail to meet the specification limit, but by an amount not
greater than 0,59R, is a strong indication that the product release confidence by the supplier is less than
95 %. If the latter is not acceptable by the recipient, it is recommended that the recipient contact the
supplier and arrive at a mutually satisfactory resolution.
NOTE Five results in a row that fail to meet the specification limit constitute compelling evidence (greater
than 95 % confidence) that at least one of the batches does not meet specification.
ISO 4259-2:2017(E)
Figure 2 — Flowchart for assessment of specification conformance by recipient
6.3.4 Procedure for recipient to assess conformance for a single batch of product
In the case of assessing the conformance to specification of a single batch of product, the following
example shows how to evaluate the process. The Research Octane Number (RON) specification within
[6] [7]
EN 228 tested by ISO 5164 : is used as an example. The reproducibility of RON using this method is 0,7
at the EN 228 specification of 95,0 ON (octane number) and the repeatability at the same level is 0,2 ON.
In this example, a supplier sells a batch of gasoline as compliant with EN 228 after certifying the
product at their chosen laboratory as meeting specification. The supplier RON result is 95,1 ON against
the specification of 95,0 ON and the batch is sold Free On Board (FOB). The sales contract specifies the
representative sample as the shore tank sample which is stored appropriately and in sufficient volume
for any follow-up testing.
The recipient purchases the batch and takes a sample to check for quality and the result from their
chosen laboratory is determined as 94,7, which is off-specification but within 0,59R. Subclause 6.3.1
indicates that the product fails the specification limit with 95 % confidence
...
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