Hard coal and coke — Guidance to the inspection of mechanical sampling systems

This document sets out recommended practices for the inspection of mechanical sampling systems. It serves as a guide for conformance with applicable ISO/TC 27 standards. This document 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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Status
Published
Publication Date
14-Oct-2019
Technical Committee
Drafting Committee
Current Stage
6060 - International Standard published
Start Date
15-Oct-2019
Due Date
22-Jan-2020
Completion Date
15-Oct-2019
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INTERNATIONAL ISO
STANDARD 21398
Second edition
2019-10
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 21398:2019(E)
©
ISO 2019

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ISO 21398:2019(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2019
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO 21398:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Safety . 1
5 General considerations . 2
5.1 Precision . 2
5.2 Bias . 2
5.3 Operation of sampling system . 2
6 Establishment of inspection system . 2
6.1 General . 2
6.2 Audit — External . 3
6.3 Audit — Internal . 3
6.4 Operational inspections . 3
7 Procedures . 3
7.1 Audit — External . 3
7.2 Audit — Internal . 4
7.3 Operational inspections . 5
8 Quality control . 6
8.1 General . 6
8.2 Sampling ratio . 6
8.3 Coefficient of variation . 6
8.4 Extraction ratio . 7
8.5 Sampling records . 7
8.6 Operators’ inspection report . 7
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 operator’s inspection report .18
Annex D (informative) Examples of sampling plant operations inspection summary.21
Bibliography .23
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ISO 21398:2019(E)

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 27, Solid mineral fuels, Subcommittee
SC 4, Sampling.
This second edition cancels and replaces the first edition (ISO 21398:2007), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— the normative references have been updated and the dates removed;
— the references in Clause 5 have been updated;
— Bibliographic references have been updated.
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.
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ISO 21398:2019(E)

Introduction
The objective of this document 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 21398:2019(E)
Hard coal and coke — Guidance to the inspection of
mechanical sampling systems
1 Scope
This document sets out recommended practices for the inspection of mechanical sampling systems. It
serves as a guide for conformance with applicable ISO/TC 27 standards.
This document covers general considerations including precision, mineral variability and bias,
establishment of inspection systems and inspection procedure.
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 (all parts), Hard coal and coke — Mechanical sampling
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13909-1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
audit
critical review of a mechanical sampling system, which measures its conformance with
stipulated operating specifications, undertaken by a suitably qualified independent person who is not
directly involved in the management of that system
3.2
audit
critical inspection and review of a mechanical sampling system, which measures its
conformance with stipulated operation 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 lot
Note 1 to entry: The operator is the person responsible for monitoring the sampling system on a shift-to-shift basis.
4 Safety
This document does not purport to address safety issues that can be associated with its use. It is the
responsibility of the user of this document 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.
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ISO 21398:2019(E)

5 General considerations
5.1 Precision
Precision tests 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 test should be
carried out. These tests should be in accordance with ISO 13909-7. The Manager or Supervisor should
maintain a record of the precision of sampling, preparation and analysis of each type of coal and coke
sampled with the system.
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. It is recommended
that the system be verified in accordance with ISO 13909 (all parts) procedures. Reference is made to
ISO 13909-2, and ISO 13909-5, where bias tests may be mandatory under certain conditions. When
choosing a coal or coke type for bias testing, refer to ISO 13909-8. 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 coal
or coke 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 system. For large, multi-user systems, an
operators’ inspection report, such as the example in given Annex B, should be developed.
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;
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ISO 21398:2019(E)

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 based on 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 any 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 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.
6.3 Audit — Internal
It is recommended that 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
It is recommended that 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 7.2 and 7.3. 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 system
being evaluated. It is recommended that a person who is not directly involved in the operation and
management of that sampling system carry out an audit at least once per year.
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ISO 21398:2019(E)

It is recommended that reference be made to the original operational parameters upon which the
sampling system was designed. Operational conditions such as conveyor capacity, belt speed or material
top size may 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 may result in excessive primary increment mass that can
no longer be entirely contained by the primary sample cutter.
— A change in conveyor speed may affect the trajectory of material at a transfer point, which may
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 may 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;
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 the relevant parts of ISO 13909. 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.
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ISO 21398:2019(E)

The following items should be inspected:
a) falling-stream and/or cross-belt cutter apertures, to determine that they comply with the
requirements of the relevant parts of ISO 13909 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
may 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 should confirm that
they conform to ISO 13909-2 and ISO 13909-5;
h) that the cycle time for all cutters, including dividers, should not be evenly divisible into the cycle
time of the previous division stage;
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 may 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 nominal top size of the crushed product. Variations in
product size over time may indicate that maintenance is required to screens, hammers in hammer-
mill crushers and rolls and gaps in roll crushers. Check that the crusher body and chutes are not
spilling material from the system;
k) final sample collector to determine general condition. Checks should be undertaken 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, considering 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;
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ISO 21398:2019(E)

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 may 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 may provide evidence
of restricted flow through the system, if this occurs. An example of this may 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 Formula (1):
SR
m
1
F =×1000 (1)
SR
m
2
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 % may indicate that system improvement is necessary.
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ISO 21398:2019(E)

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 several sampled sub-lots.
The data are plotted over many lots and long-term trends for a system may be monitored. Contro
...

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