SIST ISO 3171:1996
(Main)Petroleum liquids -- Automatic pipeline sampling
Petroleum liquids -- Automatic pipeline sampling
Recommends procedures for crude oil and liquid petroleum products being conveyed by pipeline. Does not apply to liquefied petroleum gases and liquefied natural gases. The principal purpose ist to give guidelines for specifying, testing, operating, maintaining and monitoring crude oil samples.
Produits pétroliers liquides -- Échantillonnage automatique en oléoduc
Naftni proizvodi - Tekoči ogljikovodiki - Avtomatično vzorčenje iz cevovodov
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ISO
INTERNATIONAL STANDARD
3171
Second edition
1988-12-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXfiYHAPOP,HAR OPI-AHM3A~Wl IlO CTAHflAPTM3A~MM
Automatic Pipeline sampling
Petroleum liquids -
Produits p6 troliers liquides - &han tillonnage au toma tiq& en olboduc
Reference number
ISO, 3171 : 1988 (E)
---------------------- Page: 1 ----------------------
ISO 3171 : 1988 (El
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bedies). The work of preparing International
Standards is normally carried out through ISO technical committees. Esch 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, govern-
mental 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.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
. the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.
International Standard ISO 3171 was prepared by Technical Committee ISO/TC 28,
Petroleum produc ts and lubrican ts.
This second edition cancels and replaces the first edition (ISO 3171 : 1975) of which it
constitutes a technical revision.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
@ International Organkation for Standardkation, 1988 0
Printed in Switzerland
ii
---------------------- Page: 2 ----------------------
ISO 3171 :1988 (EI
Page
Contents
.......................................................... 1
0 Introduction
. . . 1
1 Scope and field of application
2
2 References .
........................................................... 2
3 Definitions
Principles. . 4
4
............... 6
5 Selection of sampling Point (inotuding stream conditioning)
Profile testing. . 7
6
. . 9
7 Sampling probe design. .
9
Sampler design and installatiom .
8
10
9 Control equipment . . .
11
Flowmeasurement .
IO
12
11 Sample receivers and Containers. .
13
12 Samplehandling .
15
13 Safety precautions .
................................................ 15
14 Operating procedures
......................................... 17
15 Proving the sampling System.
........................ 20
16 Estimation of Overall sampling System uncertainty
23
17 Bibliography .
Annexes
....................................... 32
A Estimating water-in-oil dispersion
.......... 51
Example of water concentration profiletests at a crude oil terminal
B
54
..................
C Guide for initial screening of potential sampling locations
---------------------- Page: 3 ----------------------
ISO 3171 :1988 (EI
Tables
1 Recommended Sampler characteristics for crude oil and refined products . . . . 11
2 Typical operating Parameters for intermittent fixed-grab-volume Samplers . . . 16
3 Typical Sampler maintenance and Performance report for an intermittent
grabsampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4 Sampling test ratings for injected water concentrations of 1 % and above . . . 20
5 Symbols . 34
6 Suggested resistance coefficients . 36
7 Valuesofpforbends . 37
8 Expected concentration ratio. . 37
9 Acceptability of Profile . 38
10a Water concentration Profile test ata crude oil terminal (set 1) . 52
10b Water concentration Profile test at a crude oil terminal (set 2) . 53
11 Suggested minimum flow rates versus mixing elements . 54
Figures
Initial or periodic Validation of a sampling System . 24
Graphical representation of concentration profiles in a horizontal pipe . 25
Location of sampling Point . 25
Multipoint probe for Profile sampling . 26
Arrangement of multipoint probe in horizontal Pipeline for 300 mm diameter
pipelinesorlarger . 27
6 Typical timing diagram for Sampler System testing . 28
7 Bargraph presentation of automatic Profile test at three locations . 29
8 Results from Profile tests (typical profiles) . 30
9 Typical sampling Systems . 31
IO Energy rate and drop size . 45
11 Settlingrate . 47
Turbulente (diffusivity) . 49
12
52
13a Water concentration Profile test at a crude oil terminal (example 1) . . . . . . . .
53
13b Water concentration Profile test at a crude oil terminal (example 2) . . . . . . . .
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 3171 : 1988 (EI
Petroleum liquids - Automatic Pipeline sampling
This International Standard refers to existing methods of
0 Introduction
sampling and the type of equipment presently in use. lt is,
however, not intended that it should exclude new equipment
The purpose of collecting a Sample of the material flowing
not yet developed for commercial use, provided that such
through a Pipeline is to determine the mean composition and
equipment enables samples to be obtained that are represen-
quality of the bulk quantity. Samples of the bulk quantity in the
tative, and is in accordance with the general requirements and
line may be analysed to determine composition, water and sedi-
procedures of this International Standard.
ment content, or any other important attributes such as den-
sity, viscosity or, with special precautions, vapour pressure.
The annexes to this International Standard contain calculation
procedures about Pipeline mixing theory and Profile testing and
Manual methods of Pipeline sampling are adequate for
also give basic guidelines for Sampler location.
homogeneous liquids whose composition and quality do not
significantly vary with time. If this is not the case, automatic
lt is realized that in many countries some or all of the items
sampling is the recommended procedure since the continuous
covered by this International Standard are subject to man-
or repetitive extraction of small samples from a Pipeline ensures
datory regulations imposed by the laws of those countries;
that any changes in the bulk contents are reflected in the col-
such regulations must be rigorously observed. In cases of con-
lected Sample. In Order that the Sample shall be as represen-
flict between such mandatory regulations and this International
tative as possible it is essential to ensure that the recommenda-
Standard, the former should prevail.
tions of this International Standard with respect to the required
homogeneity of the liquid at the sampling location and to the
required frequency of extraction of the small samples are met.
1 Scope and field of application
Consideration should be given to having standby samples pro-
vided by manual methods that may be referred to if the
1.1 This International Standard recommends procedures to
automatic Sampler fails to perform satisfactorily; however,
be used for obtaining, by automatic means, representative
manual sampling will be subject to uncertainty if Pipeline con-
samples of crude oil and liquid Petroleum products being con-
ditions are varying. (See ISO 3170.)
veyed by Pipeline.
Although throughout this International Standard the term
The equipment and techniques described have generally been NOTE -
crude oil is used, this should be taken to include other Petroleum
used for sampling stabilized crude Oil, but may also be applied
liquids where the technique and equipment are also applicable.
to unstabilized crude oil and refined products provided con-
sideration is given to the relevant safety precautions and the
diff iculties of Sample handling.
1.2 This International Standard does not apply to the
sampling of liquefied Petroleum gases and liquefied natura1
gases.
Representative sampling of crude oil for density and water and
Sediment content is a critical process. Extensive studies have
shown that, in crude oil transfers, four distinct Steps are re-
1.3 The principal purpose of this International Standard is to
quired for determining representative values :
give guidelines for specifying, testing, operating, maintaining
and monitoring crude oil Samplers.
a) adequate stream conditioning of the Pipeline contents;
1.4 The sampling procedures for crude oil are intended to
b) reliable and effective sampling, ensuring proportionality
provide representative samples for the determination of
between sampling ratio and flow rate in the line;
a) the oil composition and quality;
c) adequate conservation and transporting of the Sample;
b) the total water content;
d) adequate conditioning and dividing into Parts for ac-
curate laboratory analysis.
c) other contaminants that are not considered to be part
of the crude oil transferred.
1
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ISO 3171 : 1988 (EI
b) and c) are in conflict, 3.2.1 intermittent Sampler: A System for extracting liquid
If the sampling procedures for a),
from a flowing stream, a Sample receiver to contain the Sample
separate samples may be required.
grabs taken from the stream, and a means for controlling the
NOTE - The results of the laboratory analysis may be used for amount of Sample taken by varying the sampling frequency or
calculating adjustments to the declared quantity of crude oil trans- grab volume in relation to flow rate.
ferred. The procedure for carrying out the adjustments does not form
part of this International Standard.
3.2.2 continuous Sampler: A System for extracting liquid
from a flowing stream which has a separating device which
1.5 Sample handling is included, covering all aspects follow-
continuously withdraws liquid from the main Pipeline in relation
ing collection to the transfer of the Sample to laboratory
to flow rate, an intermediate Sample receiver, and a means for
apparatus.
controlling secondary withdrawal to a final Sample receiver.
1.6 This International Standard describes the practices and
3.3 calculated Sample volume: The theoretical Sample
procedures believed at the present time to be the most likely to
volume obtained by multiplying the Sample grab volume by the
lead to representative sampling and hence to accurate water
number of actually collected grabs.
determination. However, the accuracy of the water determina-
tion on Pipeline samples obtained using automatic Samplers will
depend upon the arrangement and characteristics of all the 3.4 competent person: A person who by reason of his or
various elements making up the sampling System, and on the
her training, experience, and theoretical and practical
accuracy of the subsequent analytical procedures. knowledge is able to detect any defects or weaknesses in the
plant or equipment and to make an authoritative judgement as
to its suitability for further use.
A theoretical technique for evaluating the combined accuracy
of the automatic sampling System and the analytical test is
given in clause 16. A practical test procedure for field use is - This person should have sufficient authority to ensure that
NOTE
described in clause 15. the necessary action is taken following his or her recommendation.
Normally, the acceptable accuracy limits for a particular
3.5 controller: A device which governs the Operation of the
automatic sampling System will be specified in agreement
automatic Sampler in Order to provide a representative Sample.
between the interested Parties.
Table 4 of clause 15 classifies the Performance of automatic
3.6 fixed-rate Sample;
time-proportional Sample : A
sampling Systems by ratings based on the accuracy of practical
Sample taken from a Pipeline during the whole period of
test results. These ratings may be used as a guide to possible
transfer of a batch, composed of equal increments at uniform
Performance and as a basis for individual agreement.
time intervals.
3.7 flow-proportional Sample: A Sample taken from a
Pipeline during the whole period of transfer of a batch, at a rate
2 References
which is proportional to the rate of flow of the liquid through
-
the Pipeline at any instant.
ISO 3165, Sampling of Chemical products for industrial use
Safety in sampling.
3.8 grab: The Portion of liquid extracted from the pipe by a
-
ISO 3170, Petroleum products - Liquid hydrocarbons
Single actuation of the separating device. The sum of all the
Manual sampling.
portions results in a Sample.
NOTE - See also clause 17, Bibliography.
3.9 homogeneous mixture: A liquid is homogeneous if the
composition is the same at all Points. For the purposes of this
International Standard a liquid is homogeneous if the Variation
3 Definitions
in composition does not exceed the limits provided in 4.4.
For the purpose of this International Standard, the following
integrity of the Sample: The condition of being com-
definitions apply 3.10
plete and unaltered, i.e. the Sample being preserved with the
same composition as when it was taken from the bulk of the
3.1 acceptable (accuracy) limits: The limits within which
liquid.
the determined concentration of water in a Sample is accept-
able relative to the true value or other specified value, at the
95 % probability level.
3.11 isokinetic sampling: Sampling in such a manner that
the linear velocity of the liquid through the opening of the
3.2 automatic Sampler: A System capable of extracting a sampling probe is equal to the linear velocity of the liquid in the
representative Sample from the liquid flowing in a Pipe. The Pipeline at the sampling location and is in the same direction as
System consists of a sampling probe and/or a separating that of the bulk of the liquid in the Pipeline approaching the
device, an associated controller and a Sample receiver. sampling probe.
2
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ISO3171:1988 (EI
mixer: A device which provides a homogeneous mix- 3.18 Sample Container: A vessel used for the storage,
3.12
ture of the liquid within a Pipeline or Container in Order to obtain transportation and preconditioning of the total quantity, or a
Proportion of the total quantity, of the Sample for analytical
a representative Sample.
work or for division into identical small sub-samples to be
analysed.
3.12.1 powered mixer: A mixing device which depends on
an external Source of power for the energy required to mix the
liquid.
3.19 Sample handling : The conditioning, transferring,
dividing and transporting of the Sample. lt includes transferring
3.12.2
static mixer: A mixing device having no moving Parts
the Sample from the receiver to the Container and from the con-
and located within a pipe or tube. lt depends on the kinetic
tainer to the laboratory apparatus in which it is analysed.
energy of the moving liquid for the energy required to mix the
liquid.
3.20 Sample loop: A by-pass to the main Pipeline being
3.12.3 variable-geometry static mixer: A mixing device
sampled through which a representative Portion of the total
with Parts inside the pipe or tube which tan be adjusted to
flow is circulated.
modify its characteristics at different flow rates.
3.21 Sample receiver; receptacle: A vessel connected to
3.13 Pipeline: Any section of pipe used for the transfer of
the automatic Sampler in which the Sample is collected during
liquid. An unobstructed pipe does not have any internal fittings
the samplisitg Operation. A receiver may be permanently at-
such as a static mixer or orifice plate.
tached to .the Sampler or it may be portable. In either case, it
should be designed to maintain the integrity of the Sample.
3.14 Profile testing: A technique for simultaneous sampling
at several Points across the diameter of a Pipe. Terms used in
NOTE - In certain circumstances, it is possible to collect the total
connection with Profile testing are as follows:
Sample in more than one Sample receiver. In such circumstances, the
Sample integrjty has to be maintained for each individual Sample
volume.
The average of either the Point
3.14.1 Overall mean :
averages or the Profile averages. (Note that the result is the
Same.1
3.22 Sampler Performance factor (PF) : The ratio between
the accumultited Sample volume and the calculated Sample
3.14.2 Point: A Single sampling orifice in the Profile.
volume (see14.6).
3.14.3 Point average: The average of the water concentra-
tion at the same Point in all profiles (neglect Points with less
3.23 sampling frequency: The number of grabs taken in
than 1 % watet=).
unit time.
3.14.4 Profile: A set of samples taken simultaneously at
several Points across a diameter of the Pipe. 3.24 sampling interval: The time between successive
grabs.
NOTE - The term is also used to denote the series of sampling Points
themselves and the set of results obtained by analysis of the samples
taken at these Points.
3.25 sampling location: The Cross-section of the pipe
where the sampling probe is, or is proposed to be, located.
3.14.5 Profile average: The average of the water concentra-
tion at each Point in the same Profile (neglect the Profile if it has
3.26 sampling probe: The Sampler element that extends
less than 1 % water).
into the Pipeline:
3.15 representative Sample: A Sample having its physical
or Chemical characteristics identical to the average charac-
3.27 sampling ratio : The quantity of Pipeline contents
teristics of the total volume being sampled.
represented by one grab.
NOTE - Since errors cannot be quantified exactly, compliance with
NOTE - lt tan beJexpressed as either the
volume, in cubic metres
Per
this ideal tan only be expressed as an uncertainty that tan be obtained
grab, or the equiva4ent length of Pipeline, in metres per grab.
either from practical tests or by theoretical calculation.
3.16 Sample: The Portion of liquid extracted from the
3.28 separating; device: A device that separates a small
Pipeline that is subsequently transferred to the laboratory for
volume of liquid from the batch of liquid that the small volume
analysis.
represents.
3.17 Sample conditioning : Homogenization necessary to
stablize the Sample during Sample handling in preparation for 3.29 stream conditioning : The distribution and dispersion
analysis. of the Pipeline contents, upstream of the sampling location.
3
---------------------- Page: 7 ----------------------
ISO 3171 : 1988 (El
This condition requires that at the sampling location:
3.30 time-proportional Sample : See 3.6.
a) the distribution or concentration of the water in the
3.31 water.
crude oil should be uniform across the section of the
Pipeline within the acceptance limits given in 4.4;
3.31.1 dissolved water: The water contained within the oil
b) the diameter of the entry port of the sampling probe
forming a Solution at the prevailing temperature.
should be large in relation to the maximum water droplet
size. The port opening should not be smaller than 6 mm
3.31.2 suspended water: The water within the oil that is
(sec 7.3).
finely dispersed as small droplets.
NOTE - lt may, over a period of time, either collect as free water or
4.2.2 The second condition is that representativity should
become dissolved water, depending on the conditions of temperature
persist throughout the period of transfer of the batch, the com-
and pressure prevailing.
Position of which may Change between the Start and finish of
sampling. The rate of sampling, whether it is continuous or in-
3.31.3 free water: The water that exists as a separate layer
termittent, should be in proportion to the flow rate in the Pipe.
Oil.
from the Oil, and typically lies beneath the
When an intermittent Sampler is used the sampling frequency
and grab size should both be sufficient to guarantee acceptable
representativity.
suspended
3.31 .4 total water: The sum of all the dissolved,
and free water in a cargo or parcel of Oil.
Furthermore, the representativity of the Sample should be
maintained in the automatic Sampler from the sampling probe
3.32 worst-case conditions : The operating conditions for up to the final receiver. Samples should be taken with an ap-
pliance that camplies with the recommendations in clauses 7,
the Sampler that present the most uneven and unstable con-
centration Profile at the sampling location. 8, 9 and 10.
NOTE - This will usually be at minimum flow rate, minimum oil den-
sity and minimum oil viscosity but may also be influenced by other
4.2.3 The third condition is that the Sample should be main-
factors such as emulsifiers and surfactants.
tained in the same condition as at the Point of extraction,
without loss from it of liquid, solids or gases and without
contamination.
4 Principles
Storage and transfer of samples should comply with the recom-
mendations in clause 11.
4.1 Purpose
This clause defines the principles which it is essential to
4.2.4 The fourth condition concerns division of a Sample into
observe during sampling operations in Order that the represen-
a number of sub-samples in such a way as to ensure that each
tativity of the Sample taken corresponds to the specifications of
of them has exactly the same composition as the original
this International Standard, and meets the acceptability criteria
Sample.
given in 4.4.
The procedure for dividing each Sample into sub-samples, and
4.2 Principles to be observed
for transferring them to laboratory appliances, is given in
clause 12.
In Order to determine the oil composition, quality and total
water content of a batch of crude Oil, samples that are
NOTE - lt should be emphasized that this fourth condition concerns a
representative of the batch are taken and analysed. The batch
critical activity and any error introduced is capable of destroying the
may be either a discrete Pipeline transfer over a given period of representativity achieved by the first three.
time, or the whole or part of the cargo of a tanker, either
loading or unloading.
4.3 Sampling tolerantes and Validation
Representativity depends on four conditions, all of which
should be observed, since failure to comply with any one of
In Order to ensure that each Sample sent to the laboratory for
them could affect the quality of the final result.
analysis is representative of the whole batch, the composition
of the Sample should not differ from the composition of the
batch by more than the tolerantes given in table 4 and as
4.2.1 The first condition is that the samples that are taken
applied in 15.5.
from the Pipeline should have the same composition as the
average composition of the crude oil over the whole cross-
In Order to ensure that any departure from the conditions given
section of the Pipeline at the location and time of sampling. lt is
above (see 4.2) does not result in a Sample representativity
not easy to comply with this condition, because of the possi-
which exceeds the tolerantes given in table 4, each step of the
bility of a variable concentration gradient existing across the
section. sampling Operation should be validated as shown in figure 1.
4
---------------------- Page: 8 ----------------------
ISO3171 :1988 (EI
4.4 General principles for sampling As there is a range of concentrations at different Points in the
Cross-section, sampling at a predetermined Point is unaccept-
able, and it will be necessary to install a mixing device (see 5.3).
Hydraulic laws governing the behaviour of heterogeneous
liquids which will mix or will not mix in the pipe show that for
NOTE - If there is any free water, or an emulsion having a high con-
stream conditioning a sufficiently high energy dissipation rate
centration of water, at the bottom of the Pipe, representative sampling
should be provided to keep drops of water and heavier solid
is not possible.
particles suspended in the crude Oil. Such an energy dissipation
rate may be provided either from the velocity in an
unobstructed Pipe, or from a mixing device immediately 4.5 Dispersed Phase - variations with time
upstream of the sampling location.
lt is unlikely that the concentration of a dispersed Phase com-
ponent in the bulk liquid will be constant with time. For
In considering the distribution of water over the Cross-section,
example in the discharge of crude oil from a marine tanker, in
the acceptable limits of the values found in the Profile test
(clause 6) should be relative to the mean concentration of water addition to more gradual changes in the base water content,
there may also be periods when peaks of relatively high concen-
in that plane and should be within + 0,05 g/lOO g for samples
having a water content up to 1 g/lOO g and should be + 5 % trations of water travel down the Pipeline. Experimental obser-
vations indicate that these “transients” may contain over 50 %
of the mean concentration (relative) for samples having a water
content greater than 1 g/lOO g [but see also case 2 (4.4.2)1. water and may be shorter than a minute in duration. Depending
on the unloading procedures, the significance of the water
discharged in the form of transients may vary relative to the
Although the concentrations a bove are quoted in mass units,
NOTE -
base level carried with the bulk of the discharged cargo.
they also apply to volume units.
lt is apparent that the representativity of samples taken in such
In a horizontal Pipe, three cases may be used to describe the
applications will be dependent upon the ability of the automatic
ways in which the concentration of the different phases may
Sampler System to reflect, both accurately and proportionally,
vary over the Cross-section of the pipe depending on hydraulic
the integrated water content of these peaks in the total col-
conditions (flow rate, product density and viscosity, dispersed
lected Sample volume.
Phase composition, interfacial tension modifiers, etc. ).
With intermittent-type Samplers, accuracy will depend on the
type of equipment and its frequency of Operation in relation to
4.4.1 Case 1 (see figure 2, Profile type 1)
the frequency and duration of the transients. With continuous-
type Samplers, accuracy will depend on the external collection
In this case, the concentration is the Same, within the accept-
and mixing arrangements and on the rate of secondary sam-
able limits as defined above, across the entire Cross-section of
pling if applied. For both types of Sampler, the Overall duration
the Pipeline for all concentrations of water. The existing con-
of the oil transfer, the duration of any water transients and the
ditions are acceptable for sampling, since water is evenly
sampling frequency have statistical significance in the deter-
distributed over the pipe Cross-section. A representative
mination of sampling accuracy.
Sample consequently exists at the inlet of the sampling probe,
which tan be placed at any Point on the diameter although it is
Theoretical analysis of the effect of dispersed Phase transients
essential that care should be taken not to place the sampling
on the Performance of the different types of Samplers leads to
probe too near the wall in Order to minimize wall effects.
the following general conclusions :
a) in short-term transfers in which there is a possibility of
4.4.2 Case 2 (see figure 2, Profile type 2)
frequent, short-duration transients, the accuracy of the
continuous type of automatic Sampler is least affected by
the transients;
b) in short-term transfers in which there may be relatively
few long-duration transients, the accuracy of the
intermittent-type Sampler approaches that of the con-
tinuous type of automatic Sampler;
c) for long-term transfers, the mean error introduced by
Sampling at this location will only be acceptable if the water
transients of any duration, using either type of Sampler, is
concentration found at the sampling Point under worst-case
within the limits of acceptability defined in this International
conditions is equal to the mean concentration within the
Standard.
acceptable limits as defined above.
4.6 Low water content
4.4.3 Case 3 (see figure 2, Profile types 3a and 3b)
Attention is drawn to the fact that, if the concentration of
In this case, the concentration across the Cross-section of the
water is about 0,l % (mlm), i.e. near the
...
SLOVENSKI STANDARD
SIST ISO 3171:1996
01-marec-1996
1DIWQLSURL]YRGL7HNRþLRJOMLNRYRGLNL$YWRPDWLþQRY]RUþHQMHL]FHYRYRGRY
Petroleum liquids -- Automatic pipeline sampling
Produits pétroliers liquides -- Échantillonnage automatique en oléoduc
Ta slovenski standard je istoveten z: ISO 3171:1988
ICS:
75.080 Naftni proizvodi na splošno Petroleum products in
general
SIST ISO 3171:1996 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
---------------------- Page: 1 ----------------------
SIST ISO 3171:1996
---------------------- Page: 2 ----------------------
SIST ISO 3171:1996
ISO
INTERNATIONAL STANDARD
3171
Second edition
1988-12-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXfiYHAPOP,HAR OPI-AHM3A~Wl IlO CTAHflAPTM3A~MM
Automatic Pipeline sampling
Petroleum liquids -
Produits p6 troliers liquides - &han tillonnage au toma tiq& en olboduc
Reference number
ISO, 3171 : 1988 (E)
---------------------- Page: 3 ----------------------
SIST ISO 3171:1996
ISO 3171 : 1988 (El
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bedies). The work of preparing International
Standards is normally carried out through ISO technical committees. Esch 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, govern-
mental 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.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
. the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.
International Standard ISO 3171 was prepared by Technical Committee ISO/TC 28,
Petroleum produc ts and lubrican ts.
This second edition cancels and replaces the first edition (ISO 3171 : 1975) of which it
constitutes a technical revision.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
@ International Organkation for Standardkation, 1988 0
Printed in Switzerland
ii
---------------------- Page: 4 ----------------------
SIST ISO 3171:1996
ISO 3171 :1988 (EI
Page
Contents
.......................................................... 1
0 Introduction
. . . 1
1 Scope and field of application
2
2 References .
........................................................... 2
3 Definitions
Principles. . 4
4
............... 6
5 Selection of sampling Point (inotuding stream conditioning)
Profile testing. . 7
6
. . 9
7 Sampling probe design. .
9
Sampler design and installatiom .
8
10
9 Control equipment . . .
11
Flowmeasurement .
IO
12
11 Sample receivers and Containers. .
13
12 Samplehandling .
15
13 Safety precautions .
................................................ 15
14 Operating procedures
......................................... 17
15 Proving the sampling System.
........................ 20
16 Estimation of Overall sampling System uncertainty
23
17 Bibliography .
Annexes
....................................... 32
A Estimating water-in-oil dispersion
.......... 51
Example of water concentration profiletests at a crude oil terminal
B
54
..................
C Guide for initial screening of potential sampling locations
---------------------- Page: 5 ----------------------
SIST ISO 3171:1996
ISO 3171 :1988 (EI
Tables
1 Recommended Sampler characteristics for crude oil and refined products . . . . 11
2 Typical operating Parameters for intermittent fixed-grab-volume Samplers . . . 16
3 Typical Sampler maintenance and Performance report for an intermittent
grabsampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4 Sampling test ratings for injected water concentrations of 1 % and above . . . 20
5 Symbols . 34
6 Suggested resistance coefficients . 36
7 Valuesofpforbends . 37
8 Expected concentration ratio. . 37
9 Acceptability of Profile . 38
10a Water concentration Profile test ata crude oil terminal (set 1) . 52
10b Water concentration Profile test at a crude oil terminal (set 2) . 53
11 Suggested minimum flow rates versus mixing elements . 54
Figures
Initial or periodic Validation of a sampling System . 24
Graphical representation of concentration profiles in a horizontal pipe . 25
Location of sampling Point . 25
Multipoint probe for Profile sampling . 26
Arrangement of multipoint probe in horizontal Pipeline for 300 mm diameter
pipelinesorlarger . 27
6 Typical timing diagram for Sampler System testing . 28
7 Bargraph presentation of automatic Profile test at three locations . 29
8 Results from Profile tests (typical profiles) . 30
9 Typical sampling Systems . 31
IO Energy rate and drop size . 45
11 Settlingrate . 47
Turbulente (diffusivity) . 49
12
52
13a Water concentration Profile test at a crude oil terminal (example 1) . . . . . . . .
53
13b Water concentration Profile test at a crude oil terminal (example 2) . . . . . . . .
---------------------- Page: 6 ----------------------
SIST ISO 3171:1996
INTERNATIONAL STANDARD ISO 3171 : 1988 (EI
Petroleum liquids - Automatic Pipeline sampling
This International Standard refers to existing methods of
0 Introduction
sampling and the type of equipment presently in use. lt is,
however, not intended that it should exclude new equipment
The purpose of collecting a Sample of the material flowing
not yet developed for commercial use, provided that such
through a Pipeline is to determine the mean composition and
equipment enables samples to be obtained that are represen-
quality of the bulk quantity. Samples of the bulk quantity in the
tative, and is in accordance with the general requirements and
line may be analysed to determine composition, water and sedi-
procedures of this International Standard.
ment content, or any other important attributes such as den-
sity, viscosity or, with special precautions, vapour pressure.
The annexes to this International Standard contain calculation
procedures about Pipeline mixing theory and Profile testing and
Manual methods of Pipeline sampling are adequate for
also give basic guidelines for Sampler location.
homogeneous liquids whose composition and quality do not
significantly vary with time. If this is not the case, automatic
lt is realized that in many countries some or all of the items
sampling is the recommended procedure since the continuous
covered by this International Standard are subject to man-
or repetitive extraction of small samples from a Pipeline ensures
datory regulations imposed by the laws of those countries;
that any changes in the bulk contents are reflected in the col-
such regulations must be rigorously observed. In cases of con-
lected Sample. In Order that the Sample shall be as represen-
flict between such mandatory regulations and this International
tative as possible it is essential to ensure that the recommenda-
Standard, the former should prevail.
tions of this International Standard with respect to the required
homogeneity of the liquid at the sampling location and to the
required frequency of extraction of the small samples are met.
1 Scope and field of application
Consideration should be given to having standby samples pro-
vided by manual methods that may be referred to if the
1.1 This International Standard recommends procedures to
automatic Sampler fails to perform satisfactorily; however,
be used for obtaining, by automatic means, representative
manual sampling will be subject to uncertainty if Pipeline con-
samples of crude oil and liquid Petroleum products being con-
ditions are varying. (See ISO 3170.)
veyed by Pipeline.
Although throughout this International Standard the term
The equipment and techniques described have generally been NOTE -
crude oil is used, this should be taken to include other Petroleum
used for sampling stabilized crude Oil, but may also be applied
liquids where the technique and equipment are also applicable.
to unstabilized crude oil and refined products provided con-
sideration is given to the relevant safety precautions and the
diff iculties of Sample handling.
1.2 This International Standard does not apply to the
sampling of liquefied Petroleum gases and liquefied natura1
gases.
Representative sampling of crude oil for density and water and
Sediment content is a critical process. Extensive studies have
shown that, in crude oil transfers, four distinct Steps are re-
1.3 The principal purpose of this International Standard is to
quired for determining representative values :
give guidelines for specifying, testing, operating, maintaining
and monitoring crude oil Samplers.
a) adequate stream conditioning of the Pipeline contents;
1.4 The sampling procedures for crude oil are intended to
b) reliable and effective sampling, ensuring proportionality
provide representative samples for the determination of
between sampling ratio and flow rate in the line;
a) the oil composition and quality;
c) adequate conservation and transporting of the Sample;
b) the total water content;
d) adequate conditioning and dividing into Parts for ac-
curate laboratory analysis.
c) other contaminants that are not considered to be part
of the crude oil transferred.
1
---------------------- Page: 7 ----------------------
SIST ISO 3171:1996
ISO 3171 : 1988 (EI
b) and c) are in conflict, 3.2.1 intermittent Sampler: A System for extracting liquid
If the sampling procedures for a),
from a flowing stream, a Sample receiver to contain the Sample
separate samples may be required.
grabs taken from the stream, and a means for controlling the
NOTE - The results of the laboratory analysis may be used for amount of Sample taken by varying the sampling frequency or
calculating adjustments to the declared quantity of crude oil trans- grab volume in relation to flow rate.
ferred. The procedure for carrying out the adjustments does not form
part of this International Standard.
3.2.2 continuous Sampler: A System for extracting liquid
from a flowing stream which has a separating device which
1.5 Sample handling is included, covering all aspects follow-
continuously withdraws liquid from the main Pipeline in relation
ing collection to the transfer of the Sample to laboratory
to flow rate, an intermediate Sample receiver, and a means for
apparatus.
controlling secondary withdrawal to a final Sample receiver.
1.6 This International Standard describes the practices and
3.3 calculated Sample volume: The theoretical Sample
procedures believed at the present time to be the most likely to
volume obtained by multiplying the Sample grab volume by the
lead to representative sampling and hence to accurate water
number of actually collected grabs.
determination. However, the accuracy of the water determina-
tion on Pipeline samples obtained using automatic Samplers will
depend upon the arrangement and characteristics of all the 3.4 competent person: A person who by reason of his or
various elements making up the sampling System, and on the
her training, experience, and theoretical and practical
accuracy of the subsequent analytical procedures. knowledge is able to detect any defects or weaknesses in the
plant or equipment and to make an authoritative judgement as
to its suitability for further use.
A theoretical technique for evaluating the combined accuracy
of the automatic sampling System and the analytical test is
given in clause 16. A practical test procedure for field use is - This person should have sufficient authority to ensure that
NOTE
described in clause 15. the necessary action is taken following his or her recommendation.
Normally, the acceptable accuracy limits for a particular
3.5 controller: A device which governs the Operation of the
automatic sampling System will be specified in agreement
automatic Sampler in Order to provide a representative Sample.
between the interested Parties.
Table 4 of clause 15 classifies the Performance of automatic
3.6 fixed-rate Sample;
time-proportional Sample : A
sampling Systems by ratings based on the accuracy of practical
Sample taken from a Pipeline during the whole period of
test results. These ratings may be used as a guide to possible
transfer of a batch, composed of equal increments at uniform
Performance and as a basis for individual agreement.
time intervals.
3.7 flow-proportional Sample: A Sample taken from a
Pipeline during the whole period of transfer of a batch, at a rate
2 References
which is proportional to the rate of flow of the liquid through
-
the Pipeline at any instant.
ISO 3165, Sampling of Chemical products for industrial use
Safety in sampling.
3.8 grab: The Portion of liquid extracted from the pipe by a
-
ISO 3170, Petroleum products - Liquid hydrocarbons
Single actuation of the separating device. The sum of all the
Manual sampling.
portions results in a Sample.
NOTE - See also clause 17, Bibliography.
3.9 homogeneous mixture: A liquid is homogeneous if the
composition is the same at all Points. For the purposes of this
International Standard a liquid is homogeneous if the Variation
3 Definitions
in composition does not exceed the limits provided in 4.4.
For the purpose of this International Standard, the following
integrity of the Sample: The condition of being com-
definitions apply 3.10
plete and unaltered, i.e. the Sample being preserved with the
same composition as when it was taken from the bulk of the
3.1 acceptable (accuracy) limits: The limits within which
liquid.
the determined concentration of water in a Sample is accept-
able relative to the true value or other specified value, at the
95 % probability level.
3.11 isokinetic sampling: Sampling in such a manner that
the linear velocity of the liquid through the opening of the
3.2 automatic Sampler: A System capable of extracting a sampling probe is equal to the linear velocity of the liquid in the
representative Sample from the liquid flowing in a Pipe. The Pipeline at the sampling location and is in the same direction as
System consists of a sampling probe and/or a separating that of the bulk of the liquid in the Pipeline approaching the
device, an associated controller and a Sample receiver. sampling probe.
2
---------------------- Page: 8 ----------------------
SIST ISO 3171:1996
ISO3171:1988 (EI
mixer: A device which provides a homogeneous mix- 3.18 Sample Container: A vessel used for the storage,
3.12
ture of the liquid within a Pipeline or Container in Order to obtain transportation and preconditioning of the total quantity, or a
Proportion of the total quantity, of the Sample for analytical
a representative Sample.
work or for division into identical small sub-samples to be
analysed.
3.12.1 powered mixer: A mixing device which depends on
an external Source of power for the energy required to mix the
liquid.
3.19 Sample handling : The conditioning, transferring,
dividing and transporting of the Sample. lt includes transferring
3.12.2
static mixer: A mixing device having no moving Parts
the Sample from the receiver to the Container and from the con-
and located within a pipe or tube. lt depends on the kinetic
tainer to the laboratory apparatus in which it is analysed.
energy of the moving liquid for the energy required to mix the
liquid.
3.20 Sample loop: A by-pass to the main Pipeline being
3.12.3 variable-geometry static mixer: A mixing device
sampled through which a representative Portion of the total
with Parts inside the pipe or tube which tan be adjusted to
flow is circulated.
modify its characteristics at different flow rates.
3.21 Sample receiver; receptacle: A vessel connected to
3.13 Pipeline: Any section of pipe used for the transfer of
the automatic Sampler in which the Sample is collected during
liquid. An unobstructed pipe does not have any internal fittings
the samplisitg Operation. A receiver may be permanently at-
such as a static mixer or orifice plate.
tached to .the Sampler or it may be portable. In either case, it
should be designed to maintain the integrity of the Sample.
3.14 Profile testing: A technique for simultaneous sampling
at several Points across the diameter of a Pipe. Terms used in
NOTE - In certain circumstances, it is possible to collect the total
connection with Profile testing are as follows:
Sample in more than one Sample receiver. In such circumstances, the
Sample integrjty has to be maintained for each individual Sample
volume.
The average of either the Point
3.14.1 Overall mean :
averages or the Profile averages. (Note that the result is the
Same.1
3.22 Sampler Performance factor (PF) : The ratio between
the accumultited Sample volume and the calculated Sample
3.14.2 Point: A Single sampling orifice in the Profile.
volume (see14.6).
3.14.3 Point average: The average of the water concentra-
tion at the same Point in all profiles (neglect Points with less
3.23 sampling frequency: The number of grabs taken in
than 1 % watet=).
unit time.
3.14.4 Profile: A set of samples taken simultaneously at
several Points across a diameter of the Pipe. 3.24 sampling interval: The time between successive
grabs.
NOTE - The term is also used to denote the series of sampling Points
themselves and the set of results obtained by analysis of the samples
taken at these Points.
3.25 sampling location: The Cross-section of the pipe
where the sampling probe is, or is proposed to be, located.
3.14.5 Profile average: The average of the water concentra-
tion at each Point in the same Profile (neglect the Profile if it has
3.26 sampling probe: The Sampler element that extends
less than 1 % water).
into the Pipeline:
3.15 representative Sample: A Sample having its physical
or Chemical characteristics identical to the average charac-
3.27 sampling ratio : The quantity of Pipeline contents
teristics of the total volume being sampled.
represented by one grab.
NOTE - Since errors cannot be quantified exactly, compliance with
NOTE - lt tan beJexpressed as either the
volume, in cubic metres
Per
this ideal tan only be expressed as an uncertainty that tan be obtained
grab, or the equiva4ent length of Pipeline, in metres per grab.
either from practical tests or by theoretical calculation.
3.16 Sample: The Portion of liquid extracted from the
3.28 separating; device: A device that separates a small
Pipeline that is subsequently transferred to the laboratory for
volume of liquid from the batch of liquid that the small volume
analysis.
represents.
3.17 Sample conditioning : Homogenization necessary to
stablize the Sample during Sample handling in preparation for 3.29 stream conditioning : The distribution and dispersion
analysis. of the Pipeline contents, upstream of the sampling location.
3
---------------------- Page: 9 ----------------------
SIST ISO 3171:1996
ISO 3171 : 1988 (El
This condition requires that at the sampling location:
3.30 time-proportional Sample : See 3.6.
a) the distribution or concentration of the water in the
3.31 water.
crude oil should be uniform across the section of the
Pipeline within the acceptance limits given in 4.4;
3.31.1 dissolved water: The water contained within the oil
b) the diameter of the entry port of the sampling probe
forming a Solution at the prevailing temperature.
should be large in relation to the maximum water droplet
size. The port opening should not be smaller than 6 mm
3.31.2 suspended water: The water within the oil that is
(sec 7.3).
finely dispersed as small droplets.
NOTE - lt may, over a period of time, either collect as free water or
4.2.2 The second condition is that representativity should
become dissolved water, depending on the conditions of temperature
persist throughout the period of transfer of the batch, the com-
and pressure prevailing.
Position of which may Change between the Start and finish of
sampling. The rate of sampling, whether it is continuous or in-
3.31.3 free water: The water that exists as a separate layer
termittent, should be in proportion to the flow rate in the Pipe.
Oil.
from the Oil, and typically lies beneath the
When an intermittent Sampler is used the sampling frequency
and grab size should both be sufficient to guarantee acceptable
representativity.
suspended
3.31 .4 total water: The sum of all the dissolved,
and free water in a cargo or parcel of Oil.
Furthermore, the representativity of the Sample should be
maintained in the automatic Sampler from the sampling probe
3.32 worst-case conditions : The operating conditions for up to the final receiver. Samples should be taken with an ap-
pliance that camplies with the recommendations in clauses 7,
the Sampler that present the most uneven and unstable con-
centration Profile at the sampling location. 8, 9 and 10.
NOTE - This will usually be at minimum flow rate, minimum oil den-
sity and minimum oil viscosity but may also be influenced by other
4.2.3 The third condition is that the Sample should be main-
factors such as emulsifiers and surfactants.
tained in the same condition as at the Point of extraction,
without loss from it of liquid, solids or gases and without
contamination.
4 Principles
Storage and transfer of samples should comply with the recom-
mendations in clause 11.
4.1 Purpose
This clause defines the principles which it is essential to
4.2.4 The fourth condition concerns division of a Sample into
observe during sampling operations in Order that the represen-
a number of sub-samples in such a way as to ensure that each
tativity of the Sample taken corresponds to the specifications of
of them has exactly the same composition as the original
this International Standard, and meets the acceptability criteria
Sample.
given in 4.4.
The procedure for dividing each Sample into sub-samples, and
4.2 Principles to be observed
for transferring them to laboratory appliances, is given in
clause 12.
In Order to determine the oil composition, quality and total
water content of a batch of crude Oil, samples that are
NOTE - lt should be emphasized that this fourth condition concerns a
representative of the batch are taken and analysed. The batch
critical activity and any error introduced is capable of destroying the
may be either a discrete Pipeline transfer over a given period of representativity achieved by the first three.
time, or the whole or part of the cargo of a tanker, either
loading or unloading.
4.3 Sampling tolerantes and Validation
Representativity depends on four conditions, all of which
should be observed, since failure to comply with any one of
In Order to ensure that each Sample sent to the laboratory for
them could affect the quality of the final result.
analysis is representative of the whole batch, the composition
of the Sample should not differ from the composition of the
batch by more than the tolerantes given in table 4 and as
4.2.1 The first condition is that the samples that are taken
applied in 15.5.
from the Pipeline should have the same composition as the
average composition of the crude oil over the whole cross-
In Order to ensure that any departure from the conditions given
section of the Pipeline at the location and time of sampling. lt is
above (see 4.2) does not result in a Sample representativity
not easy to comply with this condition, because of the possi-
which exceeds the tolerantes given in table 4, each step of the
bility of a variable concentration gradient existing across the
section. sampling Operation should be validated as shown in figure 1.
4
---------------------- Page: 10 ----------------------
SIST ISO 3171:1996
ISO3171 :1988 (EI
4.4 General principles for sampling As there is a range of concentrations at different Points in the
Cross-section, sampling at a predetermined Point is unaccept-
able, and it will be necessary to install a mixing device (see 5.3).
Hydraulic laws governing the behaviour of heterogeneous
liquids which will mix or will not mix in the pipe show that for
NOTE - If there is any free water, or an emulsion having a high con-
stream conditioning a sufficiently high energy dissipation rate
centration of water, at the bottom of the Pipe, representative sampling
should be provided to keep drops of water and heavier solid
is not possible.
particles suspended in the crude Oil. Such an energy dissipation
rate may be provided either from the velocity in an
unobstructed Pipe, or from a mixing device immediately 4.5 Dispersed Phase - variations with time
upstream of the sampling location.
lt is unlikely that the concentration of a dispersed Phase com-
ponent in the bulk liquid will be constant with time. For
In considering the distribution of water over the Cross-section,
example in the discharge of crude oil from a marine tanker, in
the acceptable limits of the values found in the Profile test
(clause 6) should be relative to the mean concentration of water addition to more gradual changes in the base water content,
there may also be periods when peaks of relatively high concen-
in that plane and should be within + 0,05 g/lOO g for samples
having a water content up to 1 g/lOO g and should be + 5 % trations of water travel down the Pipeline. Experimental obser-
vations indicate that these “transients” may contain over 50 %
of the mean concentration (relative) for samples having a water
content greater than 1 g/lOO g [but see also case 2 (4.4.2)1. water and may be shorter than a minute in duration. Depending
on the unloading procedures, the significance of the water
discharged in the form of transients may vary relative to the
Although the concentrations a bove are quoted in mass units,
NOTE -
base level carried with the bulk of the discharged cargo.
they also apply to volume units.
lt is apparent that the representativity of samples taken in such
In a horizontal Pipe, three cases may be used to describe the
applications will be dependent upon the ability of the automatic
ways in which the concentration of the different phases may
Sampler System to reflect, both accurately and proportionally,
vary over the Cross-section of the pipe depending on hydraulic
the integrated water content of these peaks in the total col-
conditions (flow rate, product density and viscosity, dispersed
lected Sample volume.
Phase composition, interfacial tension modifiers, etc. ).
With intermittent-type Samplers, accuracy will depend on the
type of equipment and its frequency of Operation in relation to
4.4.1 Case 1 (see figure 2, Profile type 1)
the frequency and duration of the transients. With continuous-
type Samplers, accuracy will depend on the external collection
In this case, the concentration is the Same, within the accept-
and mixing arrangements and on the rate of secondary sam-
able limits as defined above, across the entire Cross-section of
pling if applied. For both types of Sampler, the Overall duration
the Pipeline for all concentrations of water. The existing con-
of the oil transfer, the duration of any water transients and the
ditions are acceptable for sampling, since water is evenly
sampling frequency have statistical significance in the deter-
distributed over the pipe Cross-section. A representative
mination of sampling accuracy.
Sample consequently exists at the inlet of the sampling probe,
which tan be placed at any Point on the diameter although it is
Theoretical analysis of the effect of dispersed Phase transients
essential that care should be taken not to place the sampling
on the Performance of the different types of Samplers leads to
probe too near the wall in Order to minimize wall effects.
the following general conclusions :
a) in short-term transfers in which there is a possibility of
4.4.2 Case 2 (see figure 2, Profile type 2)
frequent, short-duration transients, the accuracy of the
continuous type of automatic Sampler is least affected by
the transients;
b) in short-term transfers in which
...
ISO
NORME INTERNATIONALE 3171
Deuxième édition
1988-12-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXaYHAPOAHAfl OPI-AHM3AYMFl f-l0 CTAHjJAPTM3A~MM
Produits pétroliers liquides - Échantillonnage
automatique en oléoduc
Au toma tic pipeline sampling
Petroleum liguids -
Numéro de référence
ISO 3171 : 1988 (F)
---------------------- Page: 1 ----------------------
ISO 3171 : 1988 (FI
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale
d’organismes nationaux de normalisation (comités membres de I’ISO). L’élaboration
des Normes internationales est en général confiée aux comités techniques de I’ISO.
Chaque comité membre intéressé par une étude a le droit de faire partie du comité
technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec I’ISO participent également aux travaux. L’ISO
collabore étroitement avec la Commission électronique internationale (CEI) en ce qui
concerne la normalisation électrotechnique.
Les projets de Normes internationales adoptés par les comités techniques sont soumis
aux comités membres pour approbation, avant leur acceptation comme Normes inter-
nationales par le Conseil de I’ISO. Les Normes internationales sont approuvées confor-
mément aux procédures de I’ISO qui requièrent l’approbation de 75 % au moins des
comités membres votants.
La Norme internationale ISO 3171 a été élaborée par le comité technique ISO/TC 28,
Produits pétroliers et lubrifian ts.
Cette deuxième édition annule et remplace première édition dont
la US0 3171 : 1 975L
elle constitue une révision technique.
L’attention des utilisateurs est attirée sur le fait que toutes les Normes internationales
sont de temps en temps soumises à révision et que toute référence faite à une autre
Norme internationale dans le présent document implique qu’il s’agit, sauf indication
contraire, de la dernière édition.
0 Organisation internationale de normalisation, 1988
Imprimé en Suisse
ii
---------------------- Page: 2 ----------------------
ISO 3171 : 1988 (FI
Page
Sommaire
Introduction. . 1
Objet et domaine d’application . 1
Références . 2
Définitions. . 2
Principes . 4
Choix du point d’échantillonnage (y compris la mise en condition
de l’écoulement) . 6
6 Testsdeprofil . 7
7 Conception de la sonde d’échantillonnage . 9
8 Conception et installation de I’échantillonneur . 10
9 Systèmedecommande. . 11
10 Mesuredudébit . 12
11 Réceptacles d’échantillon et conteneurs . 12
12 Traitement de l’échantillon . 13
Sécurité . 15
13
14 Modesopératoires . 16
Validation du systéme d’échantillonnage. . 19
15
16 Estimation de l’incertitude du systéme complet d’échantillonnage . 21
17 Bibliographie. . 24
Annexes
32
A Estimation de la dispersion de l’eau dans le pétrole . . . . . . . . . . . . . . . . . . . . . . . .
B Exemple de tests de profil de concentration en eau dans un terminal
depétrolebrut. 51
54
C Guide pour le choix des emplacements possibles d’échantillonnage. . . . . . . . . .
---------------------- Page: 3 ----------------------
IsO3171 :1988 (FI
Tableaux
1 Caractéristiques recommandées d’un échantillonneur de pétrole brut
11
et de produits raffinés. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Exemples de paramètres opératoires pour échantillonneurs discontinus
2
17
àvolumefixe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Rapport type sur les performances et l’entretien d’un échantillonneur
3
18
discontinu de PU. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E . . . . . .
4 Classification des systèmes d’échantillonnage d’après les essais
d’injection d’eau en proportion de 1 % et plus . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Symboles. 34
5
6 Coefficients de perte de pression suggérés . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
37
7 Valeur dep pour les coudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
37
8 Rapports de concentration prévus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
38
9 Critères d’acceptation des profils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IOa Test de profil de concentration en eau dans un terminal
de pétrole brut (exemple 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Test de profil de concentration en eau dans un terminal
IOb
53
de pétrole brut (exemple 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Il Vitesse minimale suggérée en fonction des éléments
54
d’homogénéisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figures
1. Diagramme de validation initiale ou périodique du système
d’échantillonnage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Représentation graphique des profils de concentration dans une
2
canalisation horizontale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Emplacement du point de soutirage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Sonde multipoints pour test de profil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Disposition d’une sonde multipoints dans une canalisation horizontale
27
pour des canalisations d’un diamètre de 300 mm ou plus . . . . . . . . . . . . . . . . .
.
28
6 Diagramme d’une séquence type du test de profil . . . . . . . . . . . . . . . . . . . . . . .
29
7 Test de profil en trois points - Diagramme à bâtons. . . . . . . . . . . . . . . . . . . . .
30
8 Résultats des tests de profil (profils caractéristiques). . . . . . . . . . . . . . . . . . . . .
31
9 Exemples de dispositifs d’échantillonnage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
45
10 Taux d’énergie et taille des gouttes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vitesse de sédimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
11
Turbulence (diffusivité) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
12
13a Test de profil de concentration en eau dans un terminal de pétrole brut
(exemple 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
13b Test de profil de concentration en eau dans un terminal de pétrole brut
53
(exemple 2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iv
---------------------- Page: 4 ----------------------
NORME INTERNATIONALE ISO 3171 : 1988 (F)
Produits pétroliers liquides - Échantillonnage
automatique en oléoduc
c) mode approprié de conservation et de transport de
0 Introduction
l’échantillon ;
Le prélèvement d’un échantillon d’un produit circulant dans
d) conditionnement et fractionnement appropriés de
une canalisation a pour but de déterminer sa composition
l’échantillon permettant de procéder à des analyses précises
moyenne et la qualité du lot complet. Les échantillons de ce lot
en laboratoire.
passant dans la canalisation peuvent être analysés pour en
déduire la composition, la teneur en eau et en sédiments ou
La présente Norme internationale se réfère aux méthodes exis-
toute autre caractéristique importante, comme la masse volu-
tantes d’échantillonnage et aux types d’équipement actuelle-
mique, la viscosité et, moyennant des précautions particulières,
ment utilisés. Toutefois, elle n’exclut pas de nouveaux équipe-
la tension de vapeur.
ments si ceux-ci permettent d’obtenir des échantillons repré-
sentatifs et s’ils répondent aux exigences générales et aux pro-
Les méthodes manuelles d’échantillonnage sur une canalisation
cédures stipulées dans la présente Norme internationale.
conviennent aux liquides homogènes dont la composition et la
qualité ne varient pas de facon significative dans le temps. Si tel
Dans les annexes de la présente Norme internationale figurent
n’est pas le cas, la méthode d’échantillonnage automatique est
les procédures de calcul relatives à la théorie de I’homogénéisa-
la méthode recommandée, du fait que le prélèvement continu
tion en ligne, les tests de profil, ainsi que des guides pour
ou répétitif de petits échantillons soutirés de la canalisation,
l’emplacement de I’échantillonneur.
garantit que toute modification intervenant dans le contenu se
répercutera dans l’échantillon obtenu. Pour que ce dernier soit
II est admis que, dans de nombreux pays, tout ou partie des
aussi représentatif que possible, il est indispensable que soient points couverts par la présente Norme internationale fait l’objet
observées les recommandations de la présente Norme interna-
de règlements imposés par la législation en vigueur dans le
tionale en ce qui concerne l’homogénéité du liquide au point
pays. Ces règlements doivent être rigoureusement observés.
d’échantillonnage et la fréquence de prélèvement des petits
En cas de conflit entre ces règlements et la présente Norme
échantillons.
internationale, ce sont les premiers qui prévalent.
On devra également envisager de pouvoir disposer d’échantil-
1 Objet et domaine d’application
lons témoins, prélevés par des méthodes manuelles et auxquel-
les on puisse se référer si I’échantillonneur automatique ne
1.1 La présente Norme internationale recommande les
fonctionne pas correctement. Néanmoins l’échantillonnage
méthodes à utiliser pour obtenir, par des moyens automati-
manuel est sujet à caution si les conditions d’écoulement chan-
ques, des échantillons représentatifs de pétrole brut ou de pro-
gent (voir ISO 3170 : 1987).
duits pétroliers liquides transportés par la canalisation.
L’équipement et les techniques décrites ont été généralement
NOTE - Bien que dans toute la présente Norme internationale on uti-
utilisés pour l’échantillonnage de pétrole brut stabilisé, mais
lise le terme «pétrole brut», celle-ci s’applique également aux autres
peuvent être également appliqués au pétrole brut non stabilisé,
produits pétroliers liquides quand les mêmes techniques et équipe-
à condition de prendre les mesures de sécurité qui s’imposent.
ments sont utilisables.
Un échantillonnage représentatif de pétrole brut, pour détermi-
1.2 La présente Norme internationale ne s’applique pas à
ner la masse volumique et la teneur en eau et en sédiments, est
l’échantillonnage de gaz de pétrole liquéfiés et de gaz naturels
une opération délicate. Des études approfondies ont montré
liquéfiés.
que lors du transfert de pétrole brut, quatre conditions sont
nécessaires pour aboutir à des valeurs réellement représentati-
1.3 L’objet principal de la présente Norme internationale est
ves :
de servir de guide pour définir, tester, mettre en œuvre, entre-
tenir et contrôler les échantillonneurs de brut.
a) conditionnement suffisant de l’écoulement du produit
circulant dans la canalisation ;
1.4 Les procédures d’échantillonnage de pétrole brut ont
pour but d’obtenir des échantillons représentatifs servant à
b) la méthode d’échantillonnage fiable et efficace, assu-
déterminer
rant une proportionnalité entre le débit d’échantillonnage et
le débit dans la canalisation; a) la composition et la qualité du pétrole;
1
---------------------- Page: 5 ----------------------
ISO 3171 : 1988 (FI
b) 3.2 échantillonneur automatique: Système capable
la teneur totale en eau;
d’extraire un échantillon représentatif d’un liquide circulant
la présence d’autres impuretés ne faisant normalement dans une canalisation. Le système comprend une sonde
cl
t transporté. d’échantillonnage et/ou un dispositif de prélèvement, un
partie du pétrole bru
Pas
système de commande associé et un réceptacle d’échantillon.
Si les procédures d’échantillonnage concernant les points a), b)
et c) sont contradictoires, il conviendra de prélever séparément
3.2.1 échantillonneur discontinu: Système pour soutirer
des échantillons. un liquide en écoulement, un réceptacle pour recevoir les prélè-
vements unitaires extraits et un système de commande permet-
NOTE - Les résultats des analyses de laboratoire peuvent être utilisés tant le contrôle de la quantité .d’échantillon prélevé en faisant
pour déterminer les corrections à appliquer aux quantités de pétrole
varier en fonction du débit, soit la fréquence d’échantillonnage,
brut transférées. Les méthodes de calcul de ces corrections ne font pas
soit le volume du prélèvement unitaire.
partie de la présente Norme internationale.
3.2.2 échantillonneur continu: Système pour soutirer un
1.5 La présente Norme internationale précise également le liquide en écoulement comportant un dispositif de prélèvement
traitement de l’échantillon depuis son prélèvement jusqu’à son
continu du liquide dans la canalisation en fonction du débit, un
transfert dans les appareils de laboratoire. réceptacle intermédiaire d’échantillon et un système de com-
mande du transfert de l’échantillon intermédiaire dans le récep-
tacle final.
1.6 La présente Norme internationale décrit les pratiques et
méthodes considérées actuellement comme les plus aptes pour
réaliser un échantillonnage représentatif et, par suite, obtenir
une détermination précise de la teneur en eau. Néanmoins, la
précision de la détermination de la teneur en eau d’échantillons
prélevés dans des canalisations à l’aide d’échantillonneurs auto-
3.4 personne qualifiée: Personne qui, en raison de sa for-
matiques dépendra des caractéristiques et de la configuration
mation, de son expérience et de ses connaissances théoriques
des divers éléments formant le système d’échantillonnage et de
et pratiques, peut déceler tout défaut ou carence au niveau de
la précision des méthodes d’analyse utilisées par la suite.
l’installation ou du matériel et juger si leur utilisation peut être
poursuivie.
Une méthode théorique pour évaluer la précision combinée du
d’échantillonnage et des procédés
système automatique
NOTE - Cette personne devra avoir une autorité suffisante pour
d’analyse est proposée au chapitre 16. Une procédure pratique
s’assurer que les actions nécessaires sont prises conformément à ses
d’essai sur place est décrite au chapitre 15.
recommandations.
Généralement, les limites de précision acceptables, pour un
3.5 système de commande: Dispositif commandant le
système particulier d’échantillonnage automatique, seront
fonctionnement de I’échantillonneur automatique pour obtenir
fixées d’un commun accord entre les parties intéressées.
un échantillon représentatif.
Le tableau 4 du chapitre 15 donne un classement des perfor-
3.6 échantillon prélevé à fréquence fixe (échantillon
mances des systèmes d’échantillonnage automatique établi à
proportionnel au temps): Échantillon constitué par une série
partir de résultats d’essais pratiques. On peut se baser sur ce
de prélèvements d’égal volume dans une canalisation, à inter-
classement pour juger des performances d’un système et con-
valles de temps réguliers, pendant toute la durée du passage
clure des accords particuliers.
d’un lot à travers cette canalisation.
3.7 échantillon proportionnel au débit: Échantillon pré-
2 Références
levé dans une canalisation pendant toute la durée du passage
d’un lot selon une fréquence proportionnelle à chaque instant
ISO 3165, Échantillonnage de produits chimiques à usage
au débit du liquide à travers cette canalisation.
indus trie1 - Sécurité dans l’échantillonnage.
ISO 3170, Produits pétroliers - Hydrocarbures liquides - 3.8 prélèvement unitaire (PU): Volume de liquide extrait
ichan tillonnage manuel. de la canalisation lors d’une action du dispositif de prélève-
ment. La somme de tous les
prélèvements unitaires constitue
Voir également chapitre 17, Bibliographie.
NOTE - l’échantillon.
mélange homogène: Un liquide est homogène si sa
39
3 Définitions
composition est la même en tous points. Dans le cadre de la
présente Norme internationale, un liquide est considéré comme
Pour les besoins de la présente Norme internationale, les défini-
homogène si sa composition ne sort pas des limites stipulées en
tions suivantes s’appl iquent.
4.4.
3.1 limites de confiance (précision) : Limites dans les- intégrité de l’échantillon: L’échantillon, dans sa tota-
3.10
quelles est acceptable une détermination de concentration en lité, ne doit subir aucune altération, c’est-à-dire, conserver la
eau dans un échantillon par rapport à la valeur réelle ou autre même composition que lorsqu’il a été prélevé dans le liquide en
valeur spécifiée pour un niveau de confiance de 95 % . mouvement.
2
---------------------- Page: 6 ----------------------
ISO 3171 : 1988 (FI
NOTE - Les erreurs ne pouvant pas être quantifiées avec précision,
3.11 échantillonnage isocinétique: Échantillonnage effec-
satisfaire à cette définition ne peut s’exprimer que sous la forme d’une
tué de telle sorte que la vitesse linéaire du liquide à travers
incertitude que l’on déterminera par mesures ou par calcul.
l’ouverture de la sonde d’échantillonnage soit égale à la vitesse
linéaire du liquide dans la canalisation, à l’endroit de la sonde,
et ait la même direction que celle du liquide dans la canalisation
3.16 échantillon: Quantité de liquide prélevée dans une
au voisinage de la sonde. canalisation et transférée, par la suite, au laboratoire pour
analyse.
3.12 homog&Msateur: Dispositif donnant un mélange
3.17 conditionnement de l’échantillon : Homogénéisation
homogéne de liquide dans une canalisation ou dans un conte-
de l’échantillon en vue de
neur, dans le but d’obtenir un échantillon représentatif. l’analyse.
3.18 conteneur: Récipient utilisé pour le stockage, le trans-
3.12.1 homogénéisateur assisté : Appareil tributaire d’une
port et le préconditionnement de la quantité totale ou d’une
source d’alimentation extérieure, fournissant l’énergie requise
partie de la quantité totale de l’échantillon, en vue’de procéder
pour homogénéiser le liquide.
à des opérations d’analyse ou de le diviser en petits sous-
échantillons identiques pour l’analyse.
3.12.2 homogénéisateur statique: Appareil sans partie
mobile, situé dans une canalisation. La puissance requise pour
3.19 traitement de l’échantillon : Conditionnement, trans-
homogénéiser le liquide en mouvement est fournie par l’énergie
fert, division et transport de l’échantillon. Ceci inclut également
cinétique du fluide.
le transvasement de l’échantillon du réceptacle dans un ou des
conteneurs et l’extraction de l’échantillon de son conteneur
3.12.3 homogénéisateur statique à géométrie variable :
pour l’introduire dans l’appareil de laboratoire où il doit être
Appareil avec partie réglable situé dans une canalisation, et
analysé.
dont on peut faire varier la position suivant le débit.
3.20 boucle d’échantillonnage et bipasse (dérivation):
3.13 canalisation: Tout ensemble de tuyauterie servant à
Circuit de dérivation de la canalisation principale dans lequel
acheminer des liquides. Une tuyauterie à passage direct ne doit
circule une portion représentative du courant principal à échan-
comporter aucun accessoire intérieur tel qu’un homogénéisa-
tillonner.
teur statique ou une plaque à orifice calibré.
3.21 réceptacle d’échantillon: Récipient, relié à I’échantil-
3.14 test de profil : Technique d’échantillonnage simultanée
lonneur automatique, dans lequel l’échantillon est recueilli. Ce
en plusieurs points sur un diamètre vertical de la canalisation.
réceptacle peut être soit fixé en permanence sur I’échantillon-
Les termes utilisés en relation avec un test de profil sont les sui-
neur, soit portatif. Dans les deux cas, il doit être concu de
vants :
manière à préserver l’intégrité de l’échantillon.
NOTE - Dans certains cas, on peut recueillir simultanément la totalité
3.14.1 moyenne générale : Moyenne des moyennes des
de l’échantillon dans plusieurs réceptacles. L’intégrité de l’échantillon
points ou moyennes des profils (noter que le résultat est le
devrait alors être assurée dans chaque réceptacle individuel.
même).
3.22 facteur de performance de I’échantillonneur (FP):
3.14.2 point: Position d’un orifice d’échantillonnage dans le
Rapport entre le volume cumulé et le volume calculé d’échantil-
profil.
lon (voir 14.6).
3.14.3 moyenne du point: Moyenne de la concentration en
3.23 fréquence d’échantillonnage: Nombre de prélève-
eau au même point de tous les profils (à l’exclusion des profils
ments unitaires (PU) par unité de temps.
ayant moins de 1 % d’eau).
3.24 période d’échantillonnage: Temps s’écoulant entre
3.14.4 profil : Série d’échantillons prélevés simultanémen t en deux PU successifs.
plusieurs points d’un diamètre verti cal de la canalisation.
3.25 emplacement du point d’échantillonnage: Section
NOTE - Ce terme est également utilisé pour indiquer les séries de
droite de la canalisation où la sonde est située, ou bien où l’on
points d’échantillonnage eux-mêmes et les séries de résultats obtenus
se propose de la placer.
par analyse des échantillons prélevés en ces points.
3.26 sonde d’échantillonnage: Élément de I’échantillon-
moyenne du profil: Moyenne des concentrations en
3.14.5
neur se prolongeant dans la canalisation.
eau de tous les points du même profil (à l’exclusion des profils
ayant moins de 1 % en eau).
3.27 taux d’échantillonnage : Quantité du contenu de la
canalisation, représentée par un PU.
3.15 échantillon représentatif: Un échantillon sera consi-
déré comme représentatif si ses caractéristiques physiques ou
NOTE - II peut être exprimé par un volume en mètres cubes par prélè-
chimiques sont identiques à la moyenne volumétrique de la vement unitaire ou par une longueur de canalisation en mètres par pré-
lèvement unitaire.
totalité du produit échantillonné.
3
---------------------- Page: 7 ----------------------
ISO 3171 : 1988 (FI
Dispositif permettant 4.2.1 La Premiere condition est que les échantillons prélevés
3.28 dispositif de prMvement :
l’extraction des prélèvements unitaires (PU). ’ dans la canalisation aient la même composition que la composi-
tion moyenne du pétrole brut dans toute la section droite de la
canalisation, au point et au moment de l’échantillonnage. Cette
3.29 conditionnement de l’koulement: Dispersion et
condition n’est pas facile à remplir du fait de la variation possi-
équirépartition de la phase dispersée du contenu de la canalisa-
ble de la concentration dans la section.
tion en amont de la sonde d’échantillonnage.
Cette condition nécessite qu’au point d’échantillonnage:
3.30 échantillon prélevé à fréquence fixe: Voir 3.6.
a) la distribution ou la concentration en eau dans le pétrole
brut soit uniforme dans toute la section droite de la canalisa-
3.31 Eau
tion, dans les limites d’acceptabilité fixées en 4.4;
.l eau dissoute: Eau contenue en solution dans le pro-
3.31 b) le diamètre de l’entrée de la sonde d’échantillonnage
duit pétrolier à la température ambiante.
soit suffisamment large par rapport aux dimensions maxi-
males des gouttelettes d’eau. II ne doit pas être inférieur à
6 mm (voir 7.3).
en susp lension : Eau présente dans le produit
3.31.2 eau
pétrolier sous forme de petites gouttelettes finement dispersées.
4.2.2 La deuxième condition est que la représentativité soit
NOTE - À terme, ces gouttelettes peuvent se rassembler en eau libre
conservée pendant toute la période de transfert du lot, dont la
ou former de l’eau dissoute, selon les conditions de température et de
composition peut changer entre le commencement et la fin de
pression du produit.
l’échantillonnage. Le débit d’échantillonnage doit être propor-
tionnel à celui existant dans la canalisation, qu’il s’agisse d’un
eau libre: Eau forma lnt une cou che distincte du produit
3.31.3
échantillonnage continu ou discontinu. Dans ce dernier cas, la
pétrolier et se trouvant sous celu i-ci de facon caractéristique.
,
fréquence de l’échantillonnage et la taille du PU doivent être
suffisantes pour garantir une représentativité acceptable.
3.31.4 eau totale: Somme des eaux libres, dissoutes et en
En outre, la représentativité de l’échantillon doit être conservée,
suspension se trouvant dans une cargaison ou un lot de produit
dans I’échantillonneur automatique, depuis son entrée dans la
pétrolier.
sonde d’échantillonnage jusqu’à son arrivée dans le réceptacle.
Les échantillons doivent être prélevés au moyen d’un appareil-
3.32 conditions les plus défavorables: Profils de concen-
lage respectant les recommandations des chapitres 7, 8, 9 et
tration les plus irréguliers et les plus instables au point d’échan-
10.
tillonnage.
NOTE - Ceci se produit généralement lorsque le débit est faible, la
4.2.3 La troisième condition est que l’échantillon soit main-
masse volumique et la viscosité sont faibles. Mais d’autres facteurs tels
tenu dans les mêmes conditions qu’au point d’extraction, sans
que les émulsifiants et les surfactants peuvent aussi intervenir.
aucune perte de liquide, de solides ou de gaz et sans contami-
nation.
4 Principes
Le stockage et le tra nsport des échantillons doivent se dérouler
comme prescri t par les recommandations du chapitre 11.
4.1 But
Le présent chapitre définit les principes auxquels il faut obéir au 4.2.4 La quatrième condition concerne la division d’un échan-
tillon en un certain nombre de sous-échantillons de telle façon
cours des opérations d’échantillonnage afin que la représentati-
vité des échantillons prélevés soit conforme aux spécifications que chacun de ces derniers ait exactement la même composi-
tion que l’échantillon d’origine.
de la présente Norme internationale et réponde aux critéres
d’acceptabilité stipulés en 4.4.
La procédure à suivre pour diviser chaque échantillon en sous-
échantillons et pour transférer ceux-ci dans les appareils de
4.2 Principes à observer
laboratoire est précisée au chapitre 12.
Pour determiner soit la composition d’un pétrole, soit la qualité
NOTE - II doit être bien entendu que cette quatrième condition est
et la teneur totale en eau, d’un lot de pétrole brut, des échantil-
fondamentale et que toute erreur introduite peut annihiler la représen-
lons représentatifs de ce lot doivent être prélevés et analysés.
tativité acquise dans les trois premières.
Le lot peut être soit un transfert par canalisation pendant une
période de temps donnée, ou être constitué de la totalité ou
d’une partie de la cargaison d’un pétrolier en cours de charge-
4.3 Tolérances d’échantillonnage et validation
ment ou de déchargement.
Pour que chaque échantillon envoyé au laboratoire pour
La représentativité dépend de quatre conditions qui devraient analyse soit représentatif de l’ensemble du lot, sa composition
toutes être respectées, car le non respect de l’une d’elles peut
par rapport à celui-ci doit rester à l’intérieur des tolérances indi-
affecter la qualité du résultat final.
quées au tableau 4 et en 15.5.
---------------------- Page: 8 ----------------------
ISO3171:1988(F)
4.4.3 Cas 3 (voir figure 2, profils de type 3a et 3b)
Pour que toute dérogation aux conditions stipulées ci-dessus
(4.2) n’aboutisse pas à ce que la représentativité de l’échantillon
II s’agit du cas où la concentration dans la section droite n’est
ne soit plus conforme aux tolérances indiquées au tableau 4,
pas linéaire, indiquant la présence d’une ségrégation (type 3a).
chaque phase de l’opération d’échantillonnage doit être vali-
On peut même trouver des profils tout à fait irréguliers
dée, comme indiqué sur la figure 1.
(type 3b).
4.4 Principes généraux d’échantillonnage
Comme il y a toute une gamme de concentration aux différents
points de la section droite, l’échantillonnage en un point déter-
Les lois hydrauliques gouvernant la ségrégation de liquides
miné est inacceptable et il est nécessaire d’installer des disposi-
hétérogénes dans la canalisation, montrent qu’il faut une quan-
tifs mélangeurs (voir 5.3).
tité suffisamment élevée d’énergie de dissipation pour que les
gouttes d’eau et les particules solides plus lourdes restent en
NOTE - S’il y a de l’eau libre ou une émulsion de concentration élevée
suspension dans le pétrole brut. Cette énergie peut être fournie
en eau à la base de la canalisation, il n’est pas possible d’obtenir un
soit par la vitesse d’écoulement dans une canalisation à section
échantillon représentatif.
libre, soit par un dispositif d’homogénéisation situé immédiate-
ment en amont du point d’échantillonnage.
4.5 Phase dispersée - variations dans le temps
Si l’on considère la distribution de l’eau dans une section droite
II est peu
...
ISO
INTERNATIONAL STANDARD
3171
Second edition
1988-12-01
INTERNATIONAL ORGANIZATION FOR STANDARDIZATION
ORGANISATION INTERNATIONALE DE NORMALISATION
MEXfiYHAPOP,HAR OPI-AHM3A~Wl IlO CTAHflAPTM3A~MM
Automatic Pipeline sampling
Petroleum liquids -
Produits p6 troliers liquides - &han tillonnage au toma tiq& en olboduc
Reference number
ISO, 3171 : 1988 (E)
---------------------- Page: 1 ----------------------
ISO 3171 : 1988 (El
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of
national Standards bodies (ISO member bedies). The work of preparing International
Standards is normally carried out through ISO technical committees. Esch 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, govern-
mental 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.
Draft International Standards adopted by the technical committees are circulated to
the member bodies for approval before their acceptance as International Standards by
. the ISO Council. They are approved in accordance with ISO procedures requiring at
least 75 % approval by the member bodies voting.
International Standard ISO 3171 was prepared by Technical Committee ISO/TC 28,
Petroleum produc ts and lubrican ts.
This second edition cancels and replaces the first edition (ISO 3171 : 1975) of which it
constitutes a technical revision.
Users should note that all International Standards undergo revision from time to time
and that any reference made herein to any other International Standard implies its
latest edition, unless otherwise stated.
@ International Organkation for Standardkation, 1988 0
Printed in Switzerland
ii
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ISO 3171 :1988 (EI
Page
Contents
.......................................................... 1
0 Introduction
. . . 1
1 Scope and field of application
2
2 References .
........................................................... 2
3 Definitions
Principles. . 4
4
............... 6
5 Selection of sampling Point (inotuding stream conditioning)
Profile testing. . 7
6
. . 9
7 Sampling probe design. .
9
Sampler design and installatiom .
8
10
9 Control equipment . . .
11
Flowmeasurement .
IO
12
11 Sample receivers and Containers. .
13
12 Samplehandling .
15
13 Safety precautions .
................................................ 15
14 Operating procedures
......................................... 17
15 Proving the sampling System.
........................ 20
16 Estimation of Overall sampling System uncertainty
23
17 Bibliography .
Annexes
....................................... 32
A Estimating water-in-oil dispersion
.......... 51
Example of water concentration profiletests at a crude oil terminal
B
54
..................
C Guide for initial screening of potential sampling locations
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ISO 3171 :1988 (EI
Tables
1 Recommended Sampler characteristics for crude oil and refined products . . . . 11
2 Typical operating Parameters for intermittent fixed-grab-volume Samplers . . . 16
3 Typical Sampler maintenance and Performance report for an intermittent
grabsampler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4 Sampling test ratings for injected water concentrations of 1 % and above . . . 20
5 Symbols . 34
6 Suggested resistance coefficients . 36
7 Valuesofpforbends . 37
8 Expected concentration ratio. . 37
9 Acceptability of Profile . 38
10a Water concentration Profile test ata crude oil terminal (set 1) . 52
10b Water concentration Profile test at a crude oil terminal (set 2) . 53
11 Suggested minimum flow rates versus mixing elements . 54
Figures
Initial or periodic Validation of a sampling System . 24
Graphical representation of concentration profiles in a horizontal pipe . 25
Location of sampling Point . 25
Multipoint probe for Profile sampling . 26
Arrangement of multipoint probe in horizontal Pipeline for 300 mm diameter
pipelinesorlarger . 27
6 Typical timing diagram for Sampler System testing . 28
7 Bargraph presentation of automatic Profile test at three locations . 29
8 Results from Profile tests (typical profiles) . 30
9 Typical sampling Systems . 31
IO Energy rate and drop size . 45
11 Settlingrate . 47
Turbulente (diffusivity) . 49
12
52
13a Water concentration Profile test at a crude oil terminal (example 1) . . . . . . . .
53
13b Water concentration Profile test at a crude oil terminal (example 2) . . . . . . . .
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INTERNATIONAL STANDARD ISO 3171 : 1988 (EI
Petroleum liquids - Automatic Pipeline sampling
This International Standard refers to existing methods of
0 Introduction
sampling and the type of equipment presently in use. lt is,
however, not intended that it should exclude new equipment
The purpose of collecting a Sample of the material flowing
not yet developed for commercial use, provided that such
through a Pipeline is to determine the mean composition and
equipment enables samples to be obtained that are represen-
quality of the bulk quantity. Samples of the bulk quantity in the
tative, and is in accordance with the general requirements and
line may be analysed to determine composition, water and sedi-
procedures of this International Standard.
ment content, or any other important attributes such as den-
sity, viscosity or, with special precautions, vapour pressure.
The annexes to this International Standard contain calculation
procedures about Pipeline mixing theory and Profile testing and
Manual methods of Pipeline sampling are adequate for
also give basic guidelines for Sampler location.
homogeneous liquids whose composition and quality do not
significantly vary with time. If this is not the case, automatic
lt is realized that in many countries some or all of the items
sampling is the recommended procedure since the continuous
covered by this International Standard are subject to man-
or repetitive extraction of small samples from a Pipeline ensures
datory regulations imposed by the laws of those countries;
that any changes in the bulk contents are reflected in the col-
such regulations must be rigorously observed. In cases of con-
lected Sample. In Order that the Sample shall be as represen-
flict between such mandatory regulations and this International
tative as possible it is essential to ensure that the recommenda-
Standard, the former should prevail.
tions of this International Standard with respect to the required
homogeneity of the liquid at the sampling location and to the
required frequency of extraction of the small samples are met.
1 Scope and field of application
Consideration should be given to having standby samples pro-
vided by manual methods that may be referred to if the
1.1 This International Standard recommends procedures to
automatic Sampler fails to perform satisfactorily; however,
be used for obtaining, by automatic means, representative
manual sampling will be subject to uncertainty if Pipeline con-
samples of crude oil and liquid Petroleum products being con-
ditions are varying. (See ISO 3170.)
veyed by Pipeline.
Although throughout this International Standard the term
The equipment and techniques described have generally been NOTE -
crude oil is used, this should be taken to include other Petroleum
used for sampling stabilized crude Oil, but may also be applied
liquids where the technique and equipment are also applicable.
to unstabilized crude oil and refined products provided con-
sideration is given to the relevant safety precautions and the
diff iculties of Sample handling.
1.2 This International Standard does not apply to the
sampling of liquefied Petroleum gases and liquefied natura1
gases.
Representative sampling of crude oil for density and water and
Sediment content is a critical process. Extensive studies have
shown that, in crude oil transfers, four distinct Steps are re-
1.3 The principal purpose of this International Standard is to
quired for determining representative values :
give guidelines for specifying, testing, operating, maintaining
and monitoring crude oil Samplers.
a) adequate stream conditioning of the Pipeline contents;
1.4 The sampling procedures for crude oil are intended to
b) reliable and effective sampling, ensuring proportionality
provide representative samples for the determination of
between sampling ratio and flow rate in the line;
a) the oil composition and quality;
c) adequate conservation and transporting of the Sample;
b) the total water content;
d) adequate conditioning and dividing into Parts for ac-
curate laboratory analysis.
c) other contaminants that are not considered to be part
of the crude oil transferred.
1
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ISO 3171 : 1988 (EI
b) and c) are in conflict, 3.2.1 intermittent Sampler: A System for extracting liquid
If the sampling procedures for a),
from a flowing stream, a Sample receiver to contain the Sample
separate samples may be required.
grabs taken from the stream, and a means for controlling the
NOTE - The results of the laboratory analysis may be used for amount of Sample taken by varying the sampling frequency or
calculating adjustments to the declared quantity of crude oil trans- grab volume in relation to flow rate.
ferred. The procedure for carrying out the adjustments does not form
part of this International Standard.
3.2.2 continuous Sampler: A System for extracting liquid
from a flowing stream which has a separating device which
1.5 Sample handling is included, covering all aspects follow-
continuously withdraws liquid from the main Pipeline in relation
ing collection to the transfer of the Sample to laboratory
to flow rate, an intermediate Sample receiver, and a means for
apparatus.
controlling secondary withdrawal to a final Sample receiver.
1.6 This International Standard describes the practices and
3.3 calculated Sample volume: The theoretical Sample
procedures believed at the present time to be the most likely to
volume obtained by multiplying the Sample grab volume by the
lead to representative sampling and hence to accurate water
number of actually collected grabs.
determination. However, the accuracy of the water determina-
tion on Pipeline samples obtained using automatic Samplers will
depend upon the arrangement and characteristics of all the 3.4 competent person: A person who by reason of his or
various elements making up the sampling System, and on the
her training, experience, and theoretical and practical
accuracy of the subsequent analytical procedures. knowledge is able to detect any defects or weaknesses in the
plant or equipment and to make an authoritative judgement as
to its suitability for further use.
A theoretical technique for evaluating the combined accuracy
of the automatic sampling System and the analytical test is
given in clause 16. A practical test procedure for field use is - This person should have sufficient authority to ensure that
NOTE
described in clause 15. the necessary action is taken following his or her recommendation.
Normally, the acceptable accuracy limits for a particular
3.5 controller: A device which governs the Operation of the
automatic sampling System will be specified in agreement
automatic Sampler in Order to provide a representative Sample.
between the interested Parties.
Table 4 of clause 15 classifies the Performance of automatic
3.6 fixed-rate Sample;
time-proportional Sample : A
sampling Systems by ratings based on the accuracy of practical
Sample taken from a Pipeline during the whole period of
test results. These ratings may be used as a guide to possible
transfer of a batch, composed of equal increments at uniform
Performance and as a basis for individual agreement.
time intervals.
3.7 flow-proportional Sample: A Sample taken from a
Pipeline during the whole period of transfer of a batch, at a rate
2 References
which is proportional to the rate of flow of the liquid through
-
the Pipeline at any instant.
ISO 3165, Sampling of Chemical products for industrial use
Safety in sampling.
3.8 grab: The Portion of liquid extracted from the pipe by a
-
ISO 3170, Petroleum products - Liquid hydrocarbons
Single actuation of the separating device. The sum of all the
Manual sampling.
portions results in a Sample.
NOTE - See also clause 17, Bibliography.
3.9 homogeneous mixture: A liquid is homogeneous if the
composition is the same at all Points. For the purposes of this
International Standard a liquid is homogeneous if the Variation
3 Definitions
in composition does not exceed the limits provided in 4.4.
For the purpose of this International Standard, the following
integrity of the Sample: The condition of being com-
definitions apply 3.10
plete and unaltered, i.e. the Sample being preserved with the
same composition as when it was taken from the bulk of the
3.1 acceptable (accuracy) limits: The limits within which
liquid.
the determined concentration of water in a Sample is accept-
able relative to the true value or other specified value, at the
95 % probability level.
3.11 isokinetic sampling: Sampling in such a manner that
the linear velocity of the liquid through the opening of the
3.2 automatic Sampler: A System capable of extracting a sampling probe is equal to the linear velocity of the liquid in the
representative Sample from the liquid flowing in a Pipe. The Pipeline at the sampling location and is in the same direction as
System consists of a sampling probe and/or a separating that of the bulk of the liquid in the Pipeline approaching the
device, an associated controller and a Sample receiver. sampling probe.
2
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ISO3171:1988 (EI
mixer: A device which provides a homogeneous mix- 3.18 Sample Container: A vessel used for the storage,
3.12
ture of the liquid within a Pipeline or Container in Order to obtain transportation and preconditioning of the total quantity, or a
Proportion of the total quantity, of the Sample for analytical
a representative Sample.
work or for division into identical small sub-samples to be
analysed.
3.12.1 powered mixer: A mixing device which depends on
an external Source of power for the energy required to mix the
liquid.
3.19 Sample handling : The conditioning, transferring,
dividing and transporting of the Sample. lt includes transferring
3.12.2
static mixer: A mixing device having no moving Parts
the Sample from the receiver to the Container and from the con-
and located within a pipe or tube. lt depends on the kinetic
tainer to the laboratory apparatus in which it is analysed.
energy of the moving liquid for the energy required to mix the
liquid.
3.20 Sample loop: A by-pass to the main Pipeline being
3.12.3 variable-geometry static mixer: A mixing device
sampled through which a representative Portion of the total
with Parts inside the pipe or tube which tan be adjusted to
flow is circulated.
modify its characteristics at different flow rates.
3.21 Sample receiver; receptacle: A vessel connected to
3.13 Pipeline: Any section of pipe used for the transfer of
the automatic Sampler in which the Sample is collected during
liquid. An unobstructed pipe does not have any internal fittings
the samplisitg Operation. A receiver may be permanently at-
such as a static mixer or orifice plate.
tached to .the Sampler or it may be portable. In either case, it
should be designed to maintain the integrity of the Sample.
3.14 Profile testing: A technique for simultaneous sampling
at several Points across the diameter of a Pipe. Terms used in
NOTE - In certain circumstances, it is possible to collect the total
connection with Profile testing are as follows:
Sample in more than one Sample receiver. In such circumstances, the
Sample integrjty has to be maintained for each individual Sample
volume.
The average of either the Point
3.14.1 Overall mean :
averages or the Profile averages. (Note that the result is the
Same.1
3.22 Sampler Performance factor (PF) : The ratio between
the accumultited Sample volume and the calculated Sample
3.14.2 Point: A Single sampling orifice in the Profile.
volume (see14.6).
3.14.3 Point average: The average of the water concentra-
tion at the same Point in all profiles (neglect Points with less
3.23 sampling frequency: The number of grabs taken in
than 1 % watet=).
unit time.
3.14.4 Profile: A set of samples taken simultaneously at
several Points across a diameter of the Pipe. 3.24 sampling interval: The time between successive
grabs.
NOTE - The term is also used to denote the series of sampling Points
themselves and the set of results obtained by analysis of the samples
taken at these Points.
3.25 sampling location: The Cross-section of the pipe
where the sampling probe is, or is proposed to be, located.
3.14.5 Profile average: The average of the water concentra-
tion at each Point in the same Profile (neglect the Profile if it has
3.26 sampling probe: The Sampler element that extends
less than 1 % water).
into the Pipeline:
3.15 representative Sample: A Sample having its physical
or Chemical characteristics identical to the average charac-
3.27 sampling ratio : The quantity of Pipeline contents
teristics of the total volume being sampled.
represented by one grab.
NOTE - Since errors cannot be quantified exactly, compliance with
NOTE - lt tan beJexpressed as either the
volume, in cubic metres
Per
this ideal tan only be expressed as an uncertainty that tan be obtained
grab, or the equiva4ent length of Pipeline, in metres per grab.
either from practical tests or by theoretical calculation.
3.16 Sample: The Portion of liquid extracted from the
3.28 separating; device: A device that separates a small
Pipeline that is subsequently transferred to the laboratory for
volume of liquid from the batch of liquid that the small volume
analysis.
represents.
3.17 Sample conditioning : Homogenization necessary to
stablize the Sample during Sample handling in preparation for 3.29 stream conditioning : The distribution and dispersion
analysis. of the Pipeline contents, upstream of the sampling location.
3
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ISO 3171 : 1988 (El
This condition requires that at the sampling location:
3.30 time-proportional Sample : See 3.6.
a) the distribution or concentration of the water in the
3.31 water.
crude oil should be uniform across the section of the
Pipeline within the acceptance limits given in 4.4;
3.31.1 dissolved water: The water contained within the oil
b) the diameter of the entry port of the sampling probe
forming a Solution at the prevailing temperature.
should be large in relation to the maximum water droplet
size. The port opening should not be smaller than 6 mm
3.31.2 suspended water: The water within the oil that is
(sec 7.3).
finely dispersed as small droplets.
NOTE - lt may, over a period of time, either collect as free water or
4.2.2 The second condition is that representativity should
become dissolved water, depending on the conditions of temperature
persist throughout the period of transfer of the batch, the com-
and pressure prevailing.
Position of which may Change between the Start and finish of
sampling. The rate of sampling, whether it is continuous or in-
3.31.3 free water: The water that exists as a separate layer
termittent, should be in proportion to the flow rate in the Pipe.
Oil.
from the Oil, and typically lies beneath the
When an intermittent Sampler is used the sampling frequency
and grab size should both be sufficient to guarantee acceptable
representativity.
suspended
3.31 .4 total water: The sum of all the dissolved,
and free water in a cargo or parcel of Oil.
Furthermore, the representativity of the Sample should be
maintained in the automatic Sampler from the sampling probe
3.32 worst-case conditions : The operating conditions for up to the final receiver. Samples should be taken with an ap-
pliance that camplies with the recommendations in clauses 7,
the Sampler that present the most uneven and unstable con-
centration Profile at the sampling location. 8, 9 and 10.
NOTE - This will usually be at minimum flow rate, minimum oil den-
sity and minimum oil viscosity but may also be influenced by other
4.2.3 The third condition is that the Sample should be main-
factors such as emulsifiers and surfactants.
tained in the same condition as at the Point of extraction,
without loss from it of liquid, solids or gases and without
contamination.
4 Principles
Storage and transfer of samples should comply with the recom-
mendations in clause 11.
4.1 Purpose
This clause defines the principles which it is essential to
4.2.4 The fourth condition concerns division of a Sample into
observe during sampling operations in Order that the represen-
a number of sub-samples in such a way as to ensure that each
tativity of the Sample taken corresponds to the specifications of
of them has exactly the same composition as the original
this International Standard, and meets the acceptability criteria
Sample.
given in 4.4.
The procedure for dividing each Sample into sub-samples, and
4.2 Principles to be observed
for transferring them to laboratory appliances, is given in
clause 12.
In Order to determine the oil composition, quality and total
water content of a batch of crude Oil, samples that are
NOTE - lt should be emphasized that this fourth condition concerns a
representative of the batch are taken and analysed. The batch
critical activity and any error introduced is capable of destroying the
may be either a discrete Pipeline transfer over a given period of representativity achieved by the first three.
time, or the whole or part of the cargo of a tanker, either
loading or unloading.
4.3 Sampling tolerantes and Validation
Representativity depends on four conditions, all of which
should be observed, since failure to comply with any one of
In Order to ensure that each Sample sent to the laboratory for
them could affect the quality of the final result.
analysis is representative of the whole batch, the composition
of the Sample should not differ from the composition of the
batch by more than the tolerantes given in table 4 and as
4.2.1 The first condition is that the samples that are taken
applied in 15.5.
from the Pipeline should have the same composition as the
average composition of the crude oil over the whole cross-
In Order to ensure that any departure from the conditions given
section of the Pipeline at the location and time of sampling. lt is
above (see 4.2) does not result in a Sample representativity
not easy to comply with this condition, because of the possi-
which exceeds the tolerantes given in table 4, each step of the
bility of a variable concentration gradient existing across the
section. sampling Operation should be validated as shown in figure 1.
4
---------------------- Page: 8 ----------------------
ISO3171 :1988 (EI
4.4 General principles for sampling As there is a range of concentrations at different Points in the
Cross-section, sampling at a predetermined Point is unaccept-
able, and it will be necessary to install a mixing device (see 5.3).
Hydraulic laws governing the behaviour of heterogeneous
liquids which will mix or will not mix in the pipe show that for
NOTE - If there is any free water, or an emulsion having a high con-
stream conditioning a sufficiently high energy dissipation rate
centration of water, at the bottom of the Pipe, representative sampling
should be provided to keep drops of water and heavier solid
is not possible.
particles suspended in the crude Oil. Such an energy dissipation
rate may be provided either from the velocity in an
unobstructed Pipe, or from a mixing device immediately 4.5 Dispersed Phase - variations with time
upstream of the sampling location.
lt is unlikely that the concentration of a dispersed Phase com-
ponent in the bulk liquid will be constant with time. For
In considering the distribution of water over the Cross-section,
example in the discharge of crude oil from a marine tanker, in
the acceptable limits of the values found in the Profile test
(clause 6) should be relative to the mean concentration of water addition to more gradual changes in the base water content,
there may also be periods when peaks of relatively high concen-
in that plane and should be within + 0,05 g/lOO g for samples
having a water content up to 1 g/lOO g and should be + 5 % trations of water travel down the Pipeline. Experimental obser-
vations indicate that these “transients” may contain over 50 %
of the mean concentration (relative) for samples having a water
content greater than 1 g/lOO g [but see also case 2 (4.4.2)1. water and may be shorter than a minute in duration. Depending
on the unloading procedures, the significance of the water
discharged in the form of transients may vary relative to the
Although the concentrations a bove are quoted in mass units,
NOTE -
base level carried with the bulk of the discharged cargo.
they also apply to volume units.
lt is apparent that the representativity of samples taken in such
In a horizontal Pipe, three cases may be used to describe the
applications will be dependent upon the ability of the automatic
ways in which the concentration of the different phases may
Sampler System to reflect, both accurately and proportionally,
vary over the Cross-section of the pipe depending on hydraulic
the integrated water content of these peaks in the total col-
conditions (flow rate, product density and viscosity, dispersed
lected Sample volume.
Phase composition, interfacial tension modifiers, etc. ).
With intermittent-type Samplers, accuracy will depend on the
type of equipment and its frequency of Operation in relation to
4.4.1 Case 1 (see figure 2, Profile type 1)
the frequency and duration of the transients. With continuous-
type Samplers, accuracy will depend on the external collection
In this case, the concentration is the Same, within the accept-
and mixing arrangements and on the rate of secondary sam-
able limits as defined above, across the entire Cross-section of
pling if applied. For both types of Sampler, the Overall duration
the Pipeline for all concentrations of water. The existing con-
of the oil transfer, the duration of any water transients and the
ditions are acceptable for sampling, since water is evenly
sampling frequency have statistical significance in the deter-
distributed over the pipe Cross-section. A representative
mination of sampling accuracy.
Sample consequently exists at the inlet of the sampling probe,
which tan be placed at any Point on the diameter although it is
Theoretical analysis of the effect of dispersed Phase transients
essential that care should be taken not to place the sampling
on the Performance of the different types of Samplers leads to
probe too near the wall in Order to minimize wall effects.
the following general conclusions :
a) in short-term transfers in which there is a possibility of
4.4.2 Case 2 (see figure 2, Profile type 2)
frequent, short-duration transients, the accuracy of the
continuous type of automatic Sampler is least affected by
the transients;
b) in short-term transfers in which there may be relatively
few long-duration transients, the accuracy of the
intermittent-type Sampler approaches that of the con-
tinuous type of automatic Sampler;
c) for long-term transfers, the mean error introduced by
Sampling at this location will only be acceptable if the water
transients of any duration, using either type of Sampler, is
concentration found at the sampling Point under worst-case
within the limits of acceptability defined in this International
conditions is equal to the mean concentration within the
Standard.
acceptable limits as defined above.
4.6 Low water content
4.4.3 Case 3 (see figure 2, Profile types 3a and 3b)
Attention is drawn to the fact that, if the concentration of
In this case, the concentration across the Cross-section of the
water is about 0,l % (mlm), i.e. near the
...
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