ISO 21398:2007
(Main)Hard coal and coke — Guidance to the inspection of mechanical sampling systems
Hard coal and coke — Guidance to the inspection of mechanical sampling systems
ISO 21398:2007 sets out recommended practices for the inspection of mechanical sampling systems. ISO 21398:2007 serves as a reference for conformance with applicable ISO/TC 27 International Standards. ISO 21398:2007 covers general considerations including precision, mineral variability and bias, establishment of inspection systems and inspection procedure.
Houille et coke — Lignes directrices pour l'inspection des systèmes d'échantillonnage mécanique
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INTERNATIONAL ISO
STANDARD 21398
First edition
2007-06-01
Hard coal and coke — Guidance to the
inspection of mechanical sampling
systems
Houille et coke — Lignes directrices pour l'inspection des systèmes
d'échantillonnage mécanique
Reference number
ISO 21398:2007(E)
©
ISO 2007
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ISO 21398:2007(E)
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ISO 21398:2007(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normatives references . 1
3 Terms and definitions. 1
4 Safety . 2
5 General considerations. 2
5.1 Precision. 2
5.2 Bias. 2
5.3 Operation of sampling system . 2
6 Establishment of inspection system . 3
6.1 General. 3
6.2 Audit — External . 3
6.3 Audit — Internal . 4
6.4 Operational inspections. 4
7 Procedures . 4
7.1 Audit — External . 4
7.2 Audit — Internal . 5
7.3 Operational inspections. 6
8 Quality control. 6
8.1 General. 6
8.2 Sampling ratio . 6
8.3 Coefficient of variation. 7
8.4 Extraction ratio. 7
8.5 Sampling records. 7
8.6 Operators’ inspection report . 8
Annex A (informative) Monitoring coal sampling ratios using control charts. 11
Annex B (informative) Examples of sampling checklists. 15
Annex C (informative) Example of sampling plant operators inspection report . 18
Annex D (informative) Example of sampling plant operations inspection summary. 23
Bibliography . 25
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ISO 21398:2007(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 21398 was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee SC 4,
Sampling.
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ISO 21398:2007(E)
Introduction
The objective of this International Standard is to provide users of new and existing mechanical sampling
systems for minerals with guidance on their operation and inspection.
An ‘informative’ annex is for information and guidance only.
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INTERNATIONAL STANDARD ISO 21398:2007(E)
Hard coal and coke — Guidance to the inspection
of mechanical sampling systems
1 Scope
This International Standard sets out recommended practices for the inspection of mechanical sampling
systems. It serves as a reference for conformance with applicable ISO/TC 27 International Standards.
This International Standard covers general considerations including precision, mineral variability and bias,
establishment of inspection systems and inspection procedure.
2 Normatives references
The following referenced documents are indispensable for the application 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, Hard coal and coke — Mechanical sampling — Part 1: General introduction
ISO 13909-2:2001, Hard coal and coke — Mechanical sampling — Part 2: Coal — Sampling from moving
streams
ISO 13909-3, Hard coal and coke — Mechanical sampling — Part 3: Coal — Sampling from stationary lots
ISO 13909-4, Hard coal and coke — Mechanical sampling — Part 4: Coal — Preparation of test samples
ISO 13909-5:2001, Hard coal and coke — Mechanical sampling — Part 5: Coke — Sampling from moving
streams
ISO 13909-6, Hard coal and coke — Mechanical sampling — Part 6: Coke — Preparation of test samples
ISO 13909-7, Hard coal and coke — Mechanical sampling — Part 7: Methods for determining the precision of
sampling, sample preparation and testing
ISO 13909-8:2001, Hard coal and coke — Mechanical sampling — Part 8: Methods of testing for bias
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909-1 and the following apply.
3.1
audit
〈external〉 critical review of a mechanical sampling system, which measures its compliance with stipulated
operating specifications, undertaken by a suitably qualified independent person who is not directly involved in
the management of that particular system
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ISO 21398:2007(E)
3.2
audit
〈internal〉 critical review of a mechanical sampling system, which measures its compliance with stipulated
operating specifications, undertaken by a suitably qualified person who is not a day-to-day operator of that
particular system
3.3
operational inspection
observations and inspections of operation conditions undertaken by the operator during sampling of a
consignment
NOTE The operator is the person responsible for monitoring the sampling system on a shift-to-shift basis.
4 Safety
This International Standard does not purport to address safety issues that can be associated with its use. It is
the responsibility of the user of this International Standard to establish appropriate safety and health practices
in line with site safety regulations and relevant Occupational Health and Safety Acts. It is highly recommended
that the auditor or inspector start by conducting a careful review of all safety rules and procedures regarding
the sampling system to be inspected.
5 General considerations
5.1 Precision
Precision checks are recommended for each coal or coke type used in the system. If there is a significant
change in a coal or coke type or a new coal or coke type introduced, then a precision check should be carried
out. The test should outline the precision of sampling, preparation and analysis of each type of material (or
coal and coke) sampled with the system. These tests shall be in accordance with ISO 13909-7.
5.2 Bias
It is recommended that, after commissioning and auditing of a new system or any major engineering
modifications of an existing system, a bias test be carried out to confirm the system. If it is intended that the
system be verified in accordance with ISO 13909 (all parts) procedures, reference is made to
ISO 13909-2:2001, Clause 10, and ISO 13909-5:2001, Clause 10, where bias tests are mandatory. When
choosing a coal or coke type for bias testing, refer to ISO 13909-8:2001, 9.1 and 9.2. It is recommended that
further bias sample pairs be taken on a regular basis to confirm that the initial bias result is still relevant. If a
significant change is made to the sampling system, or a new mineral having more difficult sampling
characteristics is introduced, a new bias test should be considered.
5.3 Operation of sampling system
The mechanical plant system should be started some time in advance of the start of conveying the mineral so
that any foreign substances (including water) are purged. Where hydraulic drives are used, sufficient time
should be allowed for the hydraulic oil and the associated system to attain temperature equilibrium. It is
recommended, particularly in multi-coal or coke sampling systems, that one primary cut be allowed to pass
through the mechanical system as a conditioner before actual sampling commences.
It is recommended that the operator review any sampling records for the plant maintained by the previous
operator. These records should include quantities of coal or coke handled and sampled, and notations as to
system malfunctions, stoppages, blockages or other deficiencies. The operator should use a suitable checklist,
such as the example given in Annex A. It is recommended that the operator complete all items on a suitable
checklist designed for the particular system. For large, multi-user systems, an operators’ inspection report,
such as the example in given Annex B, should be developed.
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ISO 21398:2007(E)
Sufficient suitably designed inspection points should be available to observe that the falling-stream and cross-
belt cutters cut the full stream of coal or coke and that cutter apertures can be inspected for blockages and
blinding.
6 Establishment of inspection system
6.1 General
6.1.1 To ensure reliable operation, it is recommended that a sampling checklist (see Annex B) and
operators’ sampling record (see Annex C) be developed with input from the following sources:
a) original design criteria;
b) sampling equipment operating and maintenance manuals;
c) management responsible for the system;
d) personnel operating or maintaining the system;
e) for a new system, the designers and commissioning personnel;
f) relevant International Standards where applicable;
6.1.2 The general method for establishing these procedures is as follows.
a) Reference should be made to ISO 13909-2 and ISO 13909-5 to ascertain the correct sampling scheme.
b) Reference should be made to the equipment supplier’s operating and maintenance manual to ascertain
correct procedures for operation and intervals for routine maintenance. The manuals can provide useful
information on the basis of the system design. Such information as conveyor rates, conveyor speeds,
material parameters (particularly sizing and variability) are significant data and should always be kept in
mind when changes are contemplated.
c) Existing sampling and maintenance records for an extended period should be examined. This information
provides guidance for operators to ensure that the required level of inspection and maintenance is carried
out to ensure reliable operation and possibly to alert operators to any inappropriate maintenance or
modifications that can have been made to the equipment.
d) Personal experience of maintenance, operational and sampling personnel should be sought with respect
to the sampling system. This information, together with that obtained from items b) and c), enable
appropriate operators’ manual, operators’ sampling record and system checklist to be prepared.
6.2 Audit — External
A scheme for regular audits of the sampling system should be established. Reference should be made to the
original operating parameters and equipment supplier's design data in order to establish conformance with the
currently applicable International Standards.
NOTE Annex B provides a typical reference list.
It is recommended that correct operation of all new systems be confirmed by an audit following the
commissioning stage before being accepted as operational. Also, the design and operation of the system
should be confirmed by an audit prior to any bias test.
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ISO 21398:2007(E)
6.3 Audit — Internal
A scheme for routine inspections of the sampling system by operators should be established. The frequency
and detail of inspections is determined by such factors as, but not limited to, reliability of the system, handling
characteristics of the sampled material and frequency of use of the system and purpose of sampling
(e.g. process control compared to large multi-user port facilities).
6.4 Operational inspections
Operational procedures and inspections should be established and carried out immediately before, during and
immediately after operation of the sampling system for a given lot or sub-lot. These procedures and
inspections are less extensive than those undertaken as audits or mechanical inspections as given in 6.2 and
6.3. They should be designed to be simple inspections of the integrity of the sampling process. For large,
multi-user facilities, it is recommended that a system of operational reports, as per the example in Annex B, be
developed.
7 Procedures
7.1 Audit — External
When assessing the conformance of a mechanical sampling system, an auditor should refer to Annexes A
and B, the relevant parts of ISO 13909-2 and ISO 13909-5, and the design flow chart of the particular system
being evaluated. It is recommended that a person who is not directly involved in the operation and
management of that particular sampling system carry out an audit at least once per year.
It is essential that reference be made to the original operational parameters upon which the sampling system
is designed. Operational conditions such as conveyor capacity, belt speed or material top size can have been
altered without due regard to the impact on the operation and conformity of the sampling system.
The following are common examples of such alterations and their potential consequences.
⎯ An increase in the capacity of a conveyor can result in excessive primary increment mass that can no
longer be entirely contained by the primary sample cutter.
⎯ A change in conveyor speed can affect the trajectory of material at a transfer point, which can result in a
part of the material stream being missed by the sample cutter.
⎯ A change in nominal top size of the coal or coke can result in the original cutter aperture no longer being
large enough (i.e. three times nominal top size of the mineral) to conform to the relevant parts of
ISO 13909.
Items that should be covered as a minimum are as follows:
a) safety requirements of site;
b) original and current operating parameters;
c) selection of appropriate sampling procedure;
d) general condition of the equipment, including build-up of material or blockages in chutes, cutters and
sample loss or sample contamination. Attention should be paid to wear items or corrosion that can lead to
moisture loss from air flow through the sampling system;
e) confirmation and comparison of design and actual increment masses for all cutters at several flow rates
on the product belt, up to the maximum;
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ISO 21398:2007(E)
f) condition of cutters, cutter apertures and cutter lips. Check for foreign material such as wood, rags,
stones and material that can be blinding the cutter apertures;
g) conformity to ISO 13909. In particular, the following information should be referenced:
1) minimizing bias;
2) correct design and operation of sample cutters;
3) number of primary increments per lot or sub-lot required;
4) methods of taking primary, secondary or tertiary increments and the division of increments and/or
gross samples;
h) crusher inspection (inspect hammers or rolls and screens for wear and blinding);
i) determination of the top size of feed and crusher product;
j) staff training and procedures manual assessment;
k) check of previous mechanical inspections and operational inspections.
7.2 Audit — Internal
It is recommended that an experienced inspector should start at the primary cutter and follow through the
system to the final on-line sample collection point. The mechanical inspection should be made both with and
without coal or coke running through the system. Mechanical inspections should be carried out at more
frequent intervals than audits. For systems in daily use, it is recommended that the management of the
sampling system and not the direct operators of the system carry out mechanical inspections at least once per
month.
The following items should be inspected:
a) falling-stream and/or cross-belt cutter apertures, to determine that they comply with ISO 13909
requirements and with the design flow chart of the system;
b) speed in both directions of all cutters. For time-based sampling check that the speed is constant; for
mass-based sampling check that the speed is proportional to the flow rate to ensure that the mass of
increment is constant;
c) movement of all cutters to verify uniform speed while in the material stream;
d) that all cutters take a complete cross-section of material flow;
e) for all cutters, that the proper number of increments is taken to satisfy the requirements of ISO 13909-2
and ISO 13909-5. It should also be verified that the time or mass interval between primary cuts is correct
to assure that the minimum number of increments is collected for the lot of material being sampled during
the inspection, based on maximum attainable feed rates;
f) that all cutters are parked out of the material stream in the at-rest position and that no coal or coke is
entering the cutter opening. There should be no holes in the baffle plates, dust doors or seals that can
cause leaking of material into the primary sample hopper. In the case of slotted-belt cutters, checks
should be undertaken to confirm the aperture size, cutter lips and belt speed;
g) masses of the sample increments for falling-stream and/or cross-belt cutters to confirm that they conform
to ISO 13909-2 and ISO 13909-5;
h) that the cycle time for all cutters, including dividers, is not evenly divisible into the cycle time of the
previous division stage;
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ISO 21398:2007(E)
i) that belt feeders (sample conveyors) and vibrating feeders are in good condition. This is especially
important for sample integrity. The correct tracking of belts, condition of belts, skirt rubbers and belt
scrapers can have a significant impact on sample integrity. Check that the belt scrapers and skirts are
adjusted properly to avoid spillages. Check the flow rate settings of vibrating belt feeders;
j) the general condition of the crusher and the size of the crushed product. Variations in product size over
time can indicate that maintenance is required to screens, hammers in hammer-mill crushers and rolls
and gaps in roll crushers. Ensure the crusher body and chutes are not spilling material from the system;
k) final sample collector to determine general condition. Checks should be made to ensure that sample
integrity is not being compromised through contamination, sample loss or total moisture loss;
l) records of previous operations and inspections.
7.3 Operational inspections
Operational inspections should be carried out immediately prior to, during and immediately after each
sampling operation. This falls due at changes of shift or material type, or for each lot. The emphasis of
operational inspections should be on ensuring that the sampling system is operated at correct settings and
that reliable operation is achieved during the sampling period. It is recommended that the direct operators of
the system carry out operational inspections. The following points should be checked and reported:
a) that operational settings are correct, taking into account lot size, sub-lot size, time- or mass-based
sampling, number of primary, secondary and tertiary increments, division ratios and sample collection
interval;
b) that all equipment and sample chutes are clear of coal and coke build-up or blockages. Evidence of chute
damage due to damage to external walls or scraping should be recorded;
c) that all equipment and sample chutes are clear of foreign material such as wood, paper, rags, stones or
metal;
d) that all drives have been checked for correct operation, with attention paid to smooth operation of sample
cutter drives. Any unusual noises or vibrations should be reported;
e) that all drives, including hydraulic systems, have been started well before sampling is required. Hydraulic
systems require a period of time to attain temperature equilibrium;
f) that the sampling system has been “conditioned” by passing one or more primary increments through the
sampling system before commencing or recommencing sampling. Any sample collected during
conditioning should be discarded;
g) that control charts have been maintained in accordance with Clause 8. This provides evidence of
restricted flow through the system, if this occurs. An example of this can be found in Annex C;
8 Quality control
8.1 General
In addition to the operators’ sampling record, it is recommended that control charts also are maintained. Two
types of control charts are recommended, viz. for sampling ratio and extraction ratio.
8.2 Sampling ratio
The sampling ratio control chart is a plot of sampling ratio as a function of units sampled, where the sampling
ratio, F , is defined by Equation (1):
SR
m
1
F =× 1000 (1)
SR
m
2
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ISO 21398:2007(E)
where
m is the mass of the sample, expressed in kilograms;
1
m is the mass of the material that the sample represents, expressed in tonnes.
2
Sampling ratio comparisons should be made only for like system settings (same cutter apertures, timer
settings, sub-lot size and mass flow rate through the system). Thus, a separate control chart is required for
each set of system settings used.
Samples having a sampling ratio out of the control range are suspect and should be investigated for validity.
When there is a significant variation in the sampling ratio, the reasons for this should be investigated.
A detailed description of how to use control charts to monitor sampling ratios is provided in Annex A. An
example of sampling ratio charting is provided in Figure 1 and Table 1.
An example of an inspection summary and the associated sampling ratio control chart is shown in Table 1 and
Figure 1, respectively.
8.3 Coefficient of variation
After the sampling ratio is shown to be under control, it is good practice to monitor the percent coefficient of
variance (% CV) of the sampling ratio as an additional measure of whether the sampling process is under
control. See Annex A, Clause A.5, for instructions on how to calculate the % CV. A value for the % CV of more
than 15 % can indicate that system improvement is necessary.
8.4 Extraction ratio
The extraction ratio is the actual mass of the sample divided by the design mass of the sample expected from
the material flow rate, frequency of cuts, cutter aperture, cutter speed, etc.
The example shown in Figure 2 is calculated for a single lot. However, in practice, extraction ratio control
charts are constructed for multiple lots to indicate long-term trends. Thus, each point on an extraction ratio
control chart represents one sampled lot or the average of a number of sampled sub-lots. The data are plotted
over many lots and long-term trends for a particular system can be monitored. Control limits for the extraction
ratio are based on the average moving range. The aim in practice should be set at unity (1), not to the
average of the data. When the extraction ratio differs significantly from 1, the system should be audited and
investigated.
This ratio is useful in determining whether there are long-term problems with a particular system. For example,
if a cutter speed is reduced over several weeks due to a faulty drive, the mass of sample through the system
increases and the long-term extraction ratio data would indicate a problem with the system.
When system settings are changed, the extraction ratio is less likely to change than the sampling ratio, so it is
more useful in comparing the effectiveness of different sampling systems.
8.5 Sampling records
Records of sampling should contain the following:
a) description of sample, such as coal or coke type, shipment name, or other descriptive reference;
b) date and time each sample was taken;
c) description of any sampling problems. This should include
1) time at which problem occurred,
2) reasons for problem, such as blockage, plant failure,
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ISO 21398:2007(E)
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