ISO 13909-5:2025

International
Standard
ISO 13909-5
Third edition
Coal and coke — Mechanical
2025-07
sampling —
Part 5:
Sampling of coke from moving
streams
Charbon et coke — Échantillonnage mécanique —
Partie 5: Échantillonnage du coke en continu
Reference number
© ISO 2025
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ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Establishing a sampling scheme. 1
4.1 General .1
4.2 Design of the sampling scheme .2
4.2.1 Material to be sampled .2
4.2.2 Parameters to be determined on samples .2
4.2.3 Division of lots .2
4.2.4 Basis of sampling . .2
4.2.5 Precision of sampling .3
4.2.6 Bias of sampling .3
4.3 Precision of results .3
4.3.1 Precision and total variance .3
4.3.2 Primary increment variance .4
4.3.3 Preparation and testing variance .4
4.3.4 Number of sub-lots and number of increments in each sub-lot .5
4.4 Minimum mass of sample .8
4.5 Mass of primary increment .8
4.6 Size analysis .9
5 Methods of sampling .10
5.1 General .10
5.2 Time-basis sampling .10
5.2.1 Method of taking primary increments .10
5.2.2 Sampling interval.10
5.2.3 Mass of increment .11
5.3 Stratified random sampling .11
5.3.1 General .11
5.3.2 Time-basis stratified random sampling .11
5.4 Reference sampling .11
6 Design of mechanical samplers .11
6.1 Safety.11
6.2 Sampling system .11
6.2.1 General .11
6.2.2 Checking for precision and bias . 12
6.2.3 Operation of sampler . 12
6.3 Location of sampling equipment . 12
6.4 General requirements for designing mechanical samplers . 12
6.5 Design of falling-stream-type samplers . 13
6.5.1 General . 13
6.5.2 Cutter velocity .16
6.6 Cross-belt-type primary samplers .16
6.6.1 Operation .16
6.6.2 Design of cross-belt samplers .17
6.6.3 Maintenance of sampling equipment .18
7 Handling and storage of samples . 19
8 Sample preparation . 19
9 Minimization of bias . .20
9.1 General . 20
9.2 Spacing of increments . 20
9.3 Incorrectly extracted increments . 20

iii
9.4 Preservation of integrity of sample . 20
9.4.1 General . 20
9.4.2 Precautions to reduce bias . 20
10 Verification .21
Bibliography .22

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
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with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
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related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 27, Coal and coke, Subcommittee SC 4, Sampling.
This third edition cancels and replaces the second edition (ISO 13909-5:2016), which has been technically
revised.
The main changes are as follows:
— the title has been modified and aligned with the rest of the ISO 13909 series;
A list of all parts in the ISO 13909 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
International Standard ISO 13909-5:2025(en)
Coal and coke — Mechanical sampling —
Part 5:
Sampling of coke from moving streams
1 Scope
This document specifies procedures and requirements for the design and establishment of sampling schemes
for the mechanical sampling of coke from moving streams and the methods of sampling used.
The diversity of types of equipment for sampling and the conditions under which mechanical sampling is
performed make it inappropriate to specify standard designs for samplers which will be applicable to all
situations.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 13909-1:2025, Coal and coke — Mechanical sampling — Part 1: General introduction
ISO 13909-6, Coal and coke — Mechanical sampling — Part 6: Preparation of test samples of coke
ISO 13909-7, Coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of sampling,
sample preparation and testing
ISO 13909-8, Coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
ISO 21398, Hard coal and coke — Guidance to the inspection of mechanical sampling systems
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Establishing a sampling scheme
4.1 General
The general procedure for establishing a sampling scheme is as follows:
a) define the quality parameters to be determined and the types of samples required;
b) define the lot;
c) define or assume the precision required (see 4.3.1);

d) determine the method of combining the increments into a sample, or number of sub-lot samples, and the
method of sample preparation (see ISO 13909-6);
e) determine or assume the variability of the coke (see 4.3.2) and the variance of preparation and testing
(see 4.3.3). Methods for determining variability and the variance of preparation and testing are given in
ISO 13909-7;
f) establish the number of sub-lots and the number of increments per sub-lot required to attain the desired
precision (see 4.3.4);
g) define the sampling interval (see Clause 5);
h) ascertain the nominal top size of the coke for the purpose of determining the minimum mass of sample
(see 4.4 and Table 1). The nominal top size may initially be ascertained by consulting the consignment
details, or by visual estimation, and may be verified, if necessary, by preliminary test work;
i) determine the minimum average increment mass (see 4.5).
4.2 Design of the sampling scheme
4.2.1 Material to be sampled
The first stage in the design of the scheme is to identify the cokes to be sampled. Samples can be required
for technical evaluation, process control, quality control, and for commercial reasons by both the producer
and the customer. It is essential to ascertain exactly at what stage in the coke-handling process the sample is
required and, as far as practicable, design the scheme accordingly.
4.2.2 Parameters to be determined on samples
The samples for moisture and physical tests may be collected separately or as one sample, which is then
divided. In this document, a sample which is collected for the determination of moisture (and possibly also
for general analysis) is referred to as the moisture sample; a sample which is collected for physical tests only
is referred to as the physical sample. If a sample is used for the determination of moisture and for physical
tests, it is referred to as a common sample.
In mechanical sampling of coke, the only sample which can, in certain circumstances (see 4.2.6), be processed
automatically beyond the divided-increment stage is the moisture sample.
In order to achieve the desired precision, it may be necessary to take different numbers of increments for
the moisture and physical samples. Where a common sample is taken, the greater number of increments
shall be used.
4.2.3 Division of lots
A lot may be sampled as a whole or as a series of sub-lots, e.g. coke dispatched or delivered over a period of
time, a ship load, a train load, a wagon load, or coke produced in a certain period, e.g. a shift.
It can be necessary to divide a lot into a number of sub-lots in order to improve the precision of the results.
For lots sampled over long periods, it can be expedient to divide the lot into a series of sub-lots, obtaining a
sample for each.
4.2.4 Basis of sampling
Sampling may be carried out on either a time-basis or a mass-basis.
In time-basis sampling, increments are taken at fixed time intervals with an increment mass, collected with
a fixed speed cutter, which is proportional to the flow rate at the time of extraction.

In mass-basis sampling, increments are taken at fixed mass intervals, using a belt weigher/mass integrator,
and fixed mass increments are extracted using a variable speed cutter or sample preparation system which
produces a fixed mass divided increment.
The conditions under which mass-basis sampling can seem to offer the advantage of consistent increment
mass, for example highly variable flow rates, are those in which it is most difficult to implement in practice.
Time-basis sampling is by far the simplest to implement and is the basis of this document.
4.2.5 Precision of sampling
The required precision for a lot for each parameter to be measured shall be decided. The number of sub-lots
and minimum number of increments per sub-lot collected shall then be determined as described in 4.3.4,
and the average mass of primary increments shall be determined as described in 4.5.
For single lots, the quality variation shall be assumed as the worst case (see 4.3.2). The precision of sampling
achieved may be measured using the procedure of replicate sampling (see ISO 13909-7).
At the start of regular sampling of unknown cokes, the worst-case quality variation shall be assumed. When
sampling is in operation, a check shall be carried out to confirm that the desired precision has been achieved
using the procedure of duplicate sampling as described in ISO 13909-7.
If any subsequent change in precision is required, the number of sub-lots and increments shall be changed
as determined in 4.3.4 and the precision attained shall be rechecked. The precision shall also be checked
if there is any reason to suppose that the variability of the coke being sampled has increased. The number
of increments determined in 4.3.4 applies to the precision of the result when the sampling errors are large
relative to the testing errors, e.g. moisture content. However, in some tests, e.g. Micum Index, the testing
errors are themselves large. In this case, it may be necessary to prepare two or more test portions from the
same sample (see 4.3.4.3) and use the mean of the determinations to give a better precision.
4.2.6 Bias of sampling
It is of particular importance in sampling to ensure, as far as possible, that the parameter to be measured is
not altered by the sampling and sample preparation process or by subsequent storage prior to testing. For
example, care shall be taken to avoid breakage of coke intended for physical testing and loss of moisture
from the moisture sample during storage. This may require, in some circumstances, a limit on the minimum
mass of primary increment (see 4.5 and Clause 8).
When collecting samples for moisture determination from lots over an extended period, it can be necessary
to limit the standing time of samples by dividing the lot into a number of sub-lots (see 4.3.4).
The use of on-line crushing and division of the moisture sample for moisture determination shall be
treated with caution because of the risk of bias caused by loss of moisture in the processing (see 6.2.2). In
particular, the crushing of hot coke is not recommended. If the bias is unacceptable, the sample shall be left
in the uncrushed state and the sample preparation carried out by manual methods. However, some bias
is inevitable, whether due to breakage or loss of moisture from hot coke. The object, therefore, shall be to
restrict such degradation or moisture loss to a minimum.
When a coke-sampling scheme is implemented, it shall be checked for bias in accordance with the methods
given in ISO 13909-8.
4.3 Precision of results
4.3.1 Precision and total variance
In all methods of sampling, sample preparation and analysis, errors are incurred and the experimental
results obtained from such methods for any given parameter will deviate from the true value of that
parameter. While the absolute deviation of a single result from the “true” value cannot be determined, it is
possible to make an estimate of the precision of the experimental results. This is the closeness with which

the results of a series of measurements made on the same coke agree among themselves, and the deviation
of the mean of the results from an accepted reference value, i.e. the bias of the results (see ISO 13909-8).
It is possible to design a sampling scheme by which, in principle, an arbitrary level of precision can be
achieved.
NOTE The required overall precision for a lot is normally agreed between the parties concerned.
The theory of the estimation of precision is given in ISO 13909-7. Formula (1) is derived:
V
I
+V
PT
n
P =2 (1)
L
m
where
P is the estimated index of overall precision of sampling, sample preparation and testing for the
L
lot at a 95 % confidence level, expressed as a percentage absolute;
V is the primary increment variance;
I
V is the preparation and testing variance;
PT
n is the number of increments taken per sub-lot;
m is the number of sub-lots in the lot.
If the quality of a coke of a type not previously sampled is required, then, in order to devise a sampling
scheme, assumptions shall be made about the variability (see 4.3.2). The precision actually achieved for a
particular lot by the scheme devised can be measured by the procedures given in ISO 13909-7.
If the same type of coke is sampled regularly, sampling schemes can be laid down using data derived from
previous sampling. The procedures given in ISO 13909-7 can be used to devise the optimum scheme, thus
keeping the sampling costs to a minimum.
4.3.2 Primary increment variance
The primary increment variance, V , depends upon the type and nominal top size of coke, the degree of pre-
I
treatment and mixing, the absolute value of the parameter to be determined and the mass of increment taken.
The variability for moisture is usually higher than that for ash and hence, for the same precision, the number
of increments for moisture is adequate for ash. If, however, a higher precision is required for ash, the relevant
primary increment variance shall be applied for each sample.
The value of the primary increment variance, V , required for the calculation of the precision using
I
Formula (1) can be obtained by either
a) direct determination on the coke to be sampled using one of the methods described in ISO 13909-7; or
b) assuming a value determined for a similar coke from a similar coke handling and sampling system.
If neither of these values is available, a value of V = 5 can be assumed initially and checked, after the sampling
I
has been carried out, using one of the methods described in ISO 13909-7.
4.3.3 Preparation and testing variance
The value of the preparation and testing variance, V , required for the calculation of the precision using
PT
Formula (1) can be obtained by either:
a) direct determination on the coke to be sampled using one of the methods described in ISO 13909-7; or
b) assuming a value determined for a similar coke from a similar sample-preparation scheme.
If neither of these values is available, a value of V = 0,2 can be assumed initially and checked, after the
PT
preparation and testing has been carried out, using one of the methods described in ISO 13909-7.

4.3.4 Number of sub-lots and number of increments in each sub-lot
4.3.4.1 General
The number of increments taken from a lot in order to achieve a particular precision is a function of the
variability of the quality of the coke in the lot, irrespective of the mass of the lot. The lot may be sampled as
a whole resulting in one sample, or divided into a number of sub-lots resulting in a sample from each. Such
division may be necessary in order to achieve the required precision.
There may be other practical reasons for dividing the lot, such as:
a) for convenience when sampling over a long period;
b) to keep sample masses manageable;
c) to maintain the integrity of the sample, i.e. to avoid bias after taking the increment, particularly in order
to minimize loss of moisture due to standing. The need to do this division is dependent on factors such
as the time taken to collect samples, ambient temperature and humidity conditions, the ease of keeping
the sample in sealed containers during collection, and the particle size of the coke. It is recommended
that, if moisture loss is suspected, a bias test is carried out to compare the quality of a reference sample
immediately after extraction with the sample after standing for the normal time. If bias is found, the
sample standing time shall be reduced by collecting samples more frequently, i.e. increasing the number
of sub-lots.
The quality of the lot shall be calculated as the weighted average of the values found for the sub-lots.
As stated in 4.3.1, the precision is determined by the variability of the coke, the number of increments and
sub-lots and the preparation and testing variance. By transposing Formula (1), it can be shown that the
number of increments per sub-lot for a desired precision for a lot can be estimated from Formula (2):
4V
I
n= (2)
mP −4V
LPT
Determine the number of sub-lots required for practical reasons and then estimate the number of increments
in each for the desired precision using Formula (2). If n is a practicable number, the initial scheme is
established. However, if n is less than 10, take 10 increments per sub-lot.
A value of infinity or a negative number indicates that the errors of preparation and testing are such that the
required precision cannot be achieved with this number of sub-lots. If n is impracticably large, increase the
number of sub-lots using one of the following methods:
a) increase m to a number corresponding to a convenient mass or time, recalculate n and repeat this
process until n is a practicable number;
b) decide on the maximum practicable number of increments per sub-lot, n , and calculate m from
Formula (3):
44Vn+ V
lP1 T
m= (3)
nP
1 L
Adjust m upwards, if necessary, to a convenient number and recalculate n.
NOTE This method of calculating the number of increments required per sub-lot for a certain precision from the
primary increment variance and the preparation and testing variance generally gives a higher number for the required
number than needed. The higher number occurs because the method is based on the assumption that the quality of
coke varies in a random manner and has no serial correlation; however, serial correlation is always present to some
degree. In addition, because a certain amount of preparation and testing is required when measuring the increment
variance, the preparation and testing errors are included more than once.
The designer of a sampling scheme shall cater for the worst case anticipated and may then use higher values
for V than may actually occur when the scheme is in operation. When the sampler is commissioned, the
I
precision of the result can be estimated and adjusted (see ISO 13909-7), by increasing or decreasing the

number of increments in the sample, keeping the same increment mass so that the required precision can be
achieved at minimum cost.
Example 1
The lot is 35 000 t of 40 mm × 20 mm coke delivered in one day. The primary increment variance and
preparation and testing variance for moisture content have been determined as follows.
Primary increment variance for moisture content, V = 5.
I
Preparation and testing variance for moisture content, V = 0,10.
PT
The required precision P = 1,0 % with regard to moisture.
L
a) Initial number of sub-lots
For convenience and to avoid the sample standing for too long, take three shift samples, (i.e. m = 3).
b) Number of increments per sub-lot
45×
n= =77, using Formula (2)
31×−40× ,10
Therefore, split the lot into three sub-lots and take 10 increments from each.
Example 2
The lot is 100 000 t of 100 mm × 25 mm coke delivered as 5 000 t/day over two 8-hour shifts.
The primary increment variance, V , for moisture content is unknown, so initially assume a value of 5.
I
Required precision P = 0,25 % with regard to moisture.
L
Preparation and testing variance for moisture content, V , from experience assume a value of 0,20.
PT
a) Initial number of sub-lots
For the preliminary calculation, assume a daily sample is constituted, i.e. m = 20, in order to avoid the
risk of moisture loss by overnight storage of sample increments.
b) Number of increments per sub-lot
45×
n= =44,4 using Formula (2)
20×−02,,54×02
This number will result in too large a mass to crush as a single moisture sample for each sub-lot [almost
2 tonnes for a typical increment mass of about 45 kg using Formula (4)]. Therefore, increase the number
of sub-lots to 40, i.e. one per shift.
45×
n= =≈11,712
40×−02,,54×02
Hence, take 12 increments per shift, i.e. one every 40 min, resulting in a moisture sample of about 540 kg
for each sub-lot. However, if the equipment available for crushing the sample is not robust enough for
this sample mass, further increase the number of sub-lots.
Example 3
The lot is 9 000 t of 40 mm × 25 mm coke.
The primary increment variance for moisture content V = 5.
I
The preparation and testing variance for moisture content, V , from experience is assumed to be 0,20.
PT
The desired precision P = 0,5 % with regard to moisture content.
L
a) Number of sub-lots
For convenience, split the lot into 2 sub-lots, i.e. m = 2.
b) Number of increments per lot
45× 20
n= = ≈−66,7
−03,
20×−(,54),×02
This negative number indicates that the errors of preparation and testing are such that the required
precision cannot be achieved with this number of sub-lots.
It can be decided that 40 increments is the maximum practicable number in a sub-lot and from
Formula (3).
45×+44××00,2
m= =≈52, 6
40×05,
This gives a practical sampling method of dividing the lot into six sub-lots of 1 500 tonnes each, taking
40 increments from each.
4.3.4.2 Moisture sample
The sampling variance for moisture content can vary in the range 0,2 to 5 depending on the absolute value
of the moisture content, the size range of the coke and the extent of cutting, screening and mixing it has
undergone prior to sampling. For example, a closely graded, highly cut small-sized industrial coke sampled
on delivery to the customer would have a much lower variance than an uncut coke sampled at the wharf or
a very large coke on despatch from the producer's works. It may be known from experience what level of
variance is to be expected.
It is recommended that the number of increments initially required be sufficient to give a mass of sample
greater than the mass given in Table 1, subject to a minimum of 10 increments.
The variance for ash and other chemical properties is usually less than for moisture content. However, it is
often desired to obtain a higher precision for the ash result and hence the number of increments shall be
calculated for each and the greater number taken for the moisture sample.
Table 1 — Minimum mass of sample
Nominal top size Minimum mass
m kg
> 125 2 000
125 1 000
90 500
63 250
45 125
31,5 60
22,4 30
16,0 15
11,2 8
10,0 6
8,0 4
5,6 2
4 1
4.3.4.3 Physical sample
The cokes to be sampled within the scope of this document exhibits large differences in physical strength,
size, size range, and size distribution. In addition, different parameters, e.g. Micum test, porosity, percentage
retained on a particular sieve, mean size, etc., can be determined on the samples. Sample preparation errors
may be zero when the test is done on the whole sample or large when division of the sample takes place.
Furthermore, it is usually not possible to determine the individual increment variances for tests such as the
Micum test, because the increment mass is too small.
Many physical tests find that the only way to achieve the required precision is either:
a) to divide the lot into sub-lots; or
b) to prepare two or more test portions from the sample, taking the mean of the test results for the sample.
The precision for the particular parameter required shall then be checked and the number of increments
adjusted according to the procedure specified in ISO 13909-7.
4.4 Minimum mass of sample
For most parameters, particularly size grading and those that are particle-size related, the precision of the
result is limited by the ability of the sample to represent all the particle sizes in the mass of coke being
sampled.
The minimum mass of sample is dependent on the nominal top size of the coke, the precision required for
the parameter concerned, and the relationship of that parameter to particle size. Some such relationship
applies at all stages of preparation. The attainment of this mass will not, in itself, guarantee the required
precision. This is also dependent on the number of increments in the sample and their variability (see 4.3.4).
The masses specified in Table 1 are for guidance on the minimum mass for unknown or heterogeneous cokes.
While they can usually be reduced for the moisture sample, they may be inadequate for the determination
of, for example, oversize to 1 % precision of sampling and division, particularly on very large cokes.
When a coke is regularly sampled under the same circumstances, the precision obtained for all the required
quality parameters shall be checked in accordance with ISO 13909-7 and the masses adjusted accordingly.
However, the masses shall not be reduced below the minimum requirements laid down in the relevant
analysis standards.
Account shall also be taken of the uses to which the sample is to be put and the numbers, masses and size
distribution of the test samples required.
4.5 Mass of primary increment
The mass, m , in kilograms, of an increment taken by a mechanical cutter with cutting edges normal to the
I
stream at the discharge of a moving stream can be calculated from Formula (4):
Cb
−3
m =×10 (4)
I
36, v
C
where
C is the flow rate, in tonnes per hour;
b is the cutter aperture width, in millimetres;
v is the cutter speed, in metres per second.
C
NOTE The cutter aperture value used for calculating the mass of an increment is the distance between the leading
edges of the cutter lips first striking the stream of the material.

For a cross-belt sampler, the mass, m , in kg, of increment can be calculated from Formula (5):
I
Cb
−3
m =×10 (5)
I
36, v
B
where
C is the flow rate, in tonnes per hour;
b is the cutter aperture width, in millimetres;
v is the belt speed, in metres per second.
B
'
The minimum average mass of primary increment to be collected, m , is calculated from Formula (6):
I
m
' S
m = (6)
I
n
where
m is the minimum mass of sample (see Table 1);
S
n is the minimum number of increments taken from the sub-lot (see 4.3.4).
In most mechanical systems, the mass of primary increment collected [see Formulae (4) and (5)] will greatly
exceed that necessary to make up a sample of the required mass. In some systems, the primary increments
are therefore divided, either as taken or after reduction, in order to avoid the mass of the sample becoming
excessive.
Providing the design of the cutter conforms with the requirements of 6.5 or 6.6, the extraction of an
increment from the coke stream is unbiased whatever the flow rate at the time. Even if flow rates are
variable, increments taken at low flow rates, and hence of mass less than the average, are not subject to
extraction bias. Therefore, this document does not specify an absolute minimum increment mass.
Under some conditions, e.g. high ambient temperature, increments which are smaller than those
corresponding to the design capacity of the system may suffer from disproportionate changes in quality, e.g.
loss in moisture, and precautions need to be taken to prevent this. If such losses cannot be prevented and are
found to cause bias, such means as buffer hoppers shall be used. Alternatively, increments can themselves be
retained temporarily in a buffer hopper until there is sufficient mass to ensure passage, without introducing
bias into the system, through an on-line preparation system. On no account shall a primary sampler be
switched off at low flow rates to avoid low mass increments.
When measuring primary increment variance (see ISO 13909-7) at preliminary stages in the design of the
sampling scheme, use increment masses that are close to those expected to be taken by the system, based
on similar coke from similar sampling systems. After implementation of the sampling scheme, the precision
of the result can be estimated and adjusted (see ISO 13909-7), by increasing or decreasing the number of
increments in the sample, keeping the same increment mass.
4.6 Size analysis
Within the scope of this document, the coke products to be sampled will exhibit differences in size and
amount of fines. In addition, the parameters to be determined (percentage retained on a particular sieve,
mean size, etc.) may differ from case to case. Furthermore, when sample division is applied, division errors
shall be taken into account, whereas they are non-existent if sizing is performed without any preceding
division.
Take these factors into account when applying the techniques for calculating numbers of increments for
a particular precision (see 4.3.1 to 4.3.4). In the absence of any information on increment variance etc.,
initially take 25 increments per sample.
The precision for the particular parameter required shall then be checked and the number of increments
adjusted according to the procedure described in ISO 13909-7.

Minimization of degradation of samples used for determination of size distribution is vital to reduce bias
in the measured size distribution. To prevent particle degradation, it is essential to keep free-fall drops to
a minimum. Trial tests shall be made in accordance with the method given in ISO 13909-8 to determine the
degree of degradation.
5 Methods of sampling
5.1 General
Sampling shall be carried out by systematic sampling on a time-basis. The procedures of sample preparation
vary in accordance with the type of sampling employed (see ISO 13909-6).
It is essential that each increment taken from a stream represents the full width and depth of the stream.
The consistency of loading of the belt shall be controlled, as far as possible, so that sampling is as efficient as
possible. The flow shall be made reasonably uniform over the whole cross-section of the stream at all times,
by means of controlled loading or suitable devices such as feed hoppers, ploughs, etc.
It is essential that the increment does not completely fill or overflow the sampling device. With mechanized
sampling devices, the increment mass may be considerably larger than that necessary to produce the
calculated minimum sample mass. Hence, a system of primary increment division (see ISO 13909-6) can be
necessary to divide the increment to a manageable mass.
All processes and operations upstream of the sampling location shall be examined for characteristics which
could produce periodic variations in belt loading or quality and which may coincide with the operation of
primary samplers. Such periodicity can arise from the cycle of operations or feeder systems in use. If necessary,
modify the sampling interval, or employ stratified random sampling, to remove the possibility of bias.
5.2 Time-basis sampling
5.2.1 Method of taking primary increment
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