ISO 22031:2021

INTERNATIONAL ISO
STANDARD 22031
First edition
2021-01
Sampling and test method for
cleanable filter media taken from
filters of systems in operation
Échantillonnage et méthode d'essai pour médias filtrants
décolmatables prélevés sur des filtres de systèmes en exploitation
Reference number
ISO 22031:2021(E)
©
ISO 2021

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ISO 22031:2021(E)

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© ISO 2021
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ISO 22031:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Sampling of a representative filter element . 2
4.1 General . 2
4.2 Selection of the sampling block in the system . 3
4.2.1 Sampling block . 3
4.2.2 Number of filter elements to be sampled . 5
4.2.3 Sampling time and interval . 5
4.3 Procedure for sampling . 5
4.3.1 General. 5
4.3.2 Preparation . 5
4.3.3 Sampling of filter element. 5
4.3.4 Installation of new fabric filters . 6
4.3.5 Transportation of sampled filter elements to the test lab . 6
5 Test method for the sampled filter fabric . 6
5.1 General . 6
5.2 Appearance inspection. 7
5.3 Photography . 7
5.4 Cutting out of the test specimen . 7
5.5 Testing . 7
5.5.1 General. 7
5.5.2 Tensile strength . 7
5.5.3 Elongation ratio . 7
5.5.4 Air permeability . 8
5.5.5 Observation with a microscope . 8
5.5.6 Optional characteristics for measurement . 8
5.6 Handling of the sampled filter after the test . 8
6 Precautions for handling samples . 9
7 Test report .10
Annex A (informative) Analysing filter media damage through fault tree analysis (FTA) .11
Annex B (informative) Example of test report .14
Annex C (informative) Example of test results .18
Bibliography .22
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ISO 22031:2021(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).
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constitute an endorsement.
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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 142, Cleaning equipment for air and
other gases.
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 22031:2021(E)

Introduction
The main purpose of using dust collector systems is to remove dust particles from dirty gases. The
dry type filtering dust collectors, known as bag filters, are one of the most widespread industrial dust
collectors and are used in applications such as municipal garbage incinerators, coal fired boilers, iron
making, cement factories, power plants, etc. Especially, in municipal garbage incinerators, bag filters
[1],[2]
have been used frequently to overcome dioxin emission .
Since filter media are used under various gas and dust conditions for a long time, their physical and
[3]-[12]
chemical properties change (deteriorate) with operating time due to various causes . The
important filter characteristics such as collection performance and residual pressure drop change with
the operation period. Since users of bag filter systems have usually evaluated the parameters associated
with the change in the filter properties with their own methods, the results obtained were not easily
compared with each other. For this reason, the establishment of a standard for operation, management,
and maintenance of filter systems is important to allow prediction of the timing of replacement and/or
service life time of filter media.
Changes in the physical and chemical properties of the filter medium, i.e., physical and chemical
degradation are caused by many factors, such as heat, particle accumulation, reaction with corrosive
gases and deposited particles, and mechanical reasons like clogged weave openings and increasing
size of weave openings, the combination of those factors and so on. The filter medium damage can be
analysed through the fault tree analysis in Annex A. Clogged weave openings reduce the permeability
of the filter medium; and increasing the size of weave openings lessens the collection performance of
the filter medium. The reaction with corrosive gases and deposited particles changes properties of the
filter fibre material itself and decreases the tensile strength, tenacity, flexibility of the filter medium
and so on. These changes cause mostly adverse effects to the filter medium. This can result in the
breakage of filter media and leakage of dust to the atmosphere.
Therefore, since it is important to evaluate the property changes of filter media in order to predict the
timing of replacement and/or service life time, ISO 16891, which specifies test methods for evaluating
degradation of tensile stress of cleanable filter media, has been published. However, test methods for
other evaluation parameters such as permeability, collection efficiency, fibre diameter of used filter
media, mass and size distribution of deposited particles, have not yet been specified.
Industrial bag filter systems, in general, handle large amounts of dirty gas so that a system with a large
number of filter elements in parallel is needed to remove the dust. The degree of degradation of filter
properties depends on the location of the filter in the system because the dirty gas usually enters the
system in an irregular flow pattern. Furthermore, the method used for sampling and storage of the
used filter, and the preparation method of the test specimen should be defined. By standardizing these
test methods, it is possible to accurately assess the deterioration of individual filter media.
This document provides a standard method for sampling filter elements from a dust collector system
in operation, and a test method for monitoring sampled filter elements and the system through
measurement of basic filter properties.
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INTERNATIONAL STANDARD ISO 22031:2021(E)
Sampling and test method for cleanable filter media taken
from filters of systems in operation
1 Scope
This document specifies a method for sampling fabric filter medium from a filter system in operation,
and a test method for evaluating the degradation of the sampled filter medium. It applies to both woven
and nonwoven fabric filter media.
This document specifies a method for removing used filter medium from a dry type filtering dust
collector, a method for removing dust from the sampled filter medium as part of preparation for testing,
and measurement parameters for the test specimen. The number of filter elements to be sampled,
their positions in the blocks of filter elements in the dust collector, the position and the size of the test
specimens to be cut out from the filter element, measurement parameters and their test methods are
also specified.
This document also specifies a storage and transportation method for the sampled filter medium that
will protect the health of workers and people conducting the tests.
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 9237, Textiles — Determination of the permeability of fabrics to air
ISO 16891:2016, Test methods for evaluating degradation of characteristics of cleanable filter media
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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
air permeability
gas volume flow rate per unit filtration area at pressure drop of 124,5 Pa
[SOURCE: ISO 16891:2016, 3.2]
3.2
cleanable filter
filter designed to permit the removal of collected dust by application of an appropriate technique
[SOURCE: ISO 29464:2017, 3.2.73, modified — Note 1 to entry has been removed.]
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ISO 22031:2021(E)

3.3
degradation
change in physical and chemical performance of a filter medium caused by interaction with
corrosive gases
[SOURCE: ISO 16891:2016, 3.9]
3.4
elongation
incremental change in length of test specimen determined by tensile test
[SOURCE: ISO 16891:2016, 3.10]
3.5
nonwoven fabric
filter medium manufactured using fabric made from long fibres, bonded together with each other by
chemical, mechanical, heat or solvent treatment
[SOURCE: ISO 16891:2016, 3.21]
3.6
tensile strength
value of the maximum load divided by the width of test specimen
[SOURCE: ISO 16891:2016, 3.27]
3.7
woven fabric
filter medium manufactured using a fabric formed by weaving
[SOURCE: ISO 16891:2016, 3.31]
3.8
pulse cleaning
process for removing collected particulate from a filter element by injecting compressed air in short
bursts from the clean side (3.11) of the filter element
3.9
snap ring
metallic ring-shaped spring mounted at the open end of the filter element
3.10
dirty side
upstream side of the filter element
3.11
clean side
downstream side of the filter element
3.12
retainer
cage
device supporting the filter element as it performs dust collection
4 Sampling of a representative filter element
4.1 General
To evaluate or monitor the service life time of filter elements, it is essential to sample a representative
filter element, since the degree of degradation of filter properties depends not only on physical causes
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ISO 22031:2021(E)

but also on the location of the filter in the system. It is difficult in practice to select a representative filter
because of the size and structure of the system, arrangement of filter elements, gas flow distribution
in the system and so on, which are different for each individual system. Even in the same system, the
degree of degradation may vary significantly with the specific position of the element in the filter array.
It is often extremely difficult to identify exactly the most deteriorated filter in the system. The best
practice approach may be to choose as representative a filter element from the area in the system that
is observed to be the most deteriorated.
4.2 Selection of the sampling block in the system
4.2.1 Sampling block
The most serious deterioration is expected to appear in the area where the dirty gas concentrates. The
general location of this area depends on whether the bag filter system has a baffle plate at the dirty gas
inlet. When the dirty gas flows into the system without a baffle plate, the gas will flow to the opposite
side of the system and change the flow direction as shown in Figure 1 a) so that the representative
filter element is recommended to be sampled from a block either at the centre or at the opposite side
of the system from the dirty gas inlet, for instance, block F, C, D. When the system has a baffle plate,
the dirty gas flow is divided by the baffle plate and will come together again downstream as shown
in Figure 1 b). Therefore, the filter element is recommended to be sampled from a block where the gas
flow concentrates after it is divided by the baffle plate, for instance, block E or F. Alternatively, the
filter element can be sampled from the block identified by a flow analysis to be where the dirty gas
concentrates, for instance, block E, I, F for the left-hand side and G, I, H for the right-hand side as shown
in Figure 1 c) and d).
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ISO 22031:2021(E)

a) Bag filter system without baffle plate b) Bag filter system with baffle plate
c) Area where dirty gas flow concentrates d) Area where dirty gas flow concentrates
is already identified by flow analysis etc. is already identified by flow analysis etc.
Key
1 dirty gas entry 4 baffle plate
2 bag house 5 block of filter elements in the bag house (A to I)
3 filter element
Figure 1 — Examples of sampling block
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ISO 22031:2021(E)

4.2.2 Number of filter elements to be sampled
The number of filter elements to be sampled shall be determined by the number of blocks of filter
elements in the bag filter system.
a) Bag filter with one block: at least one sample.
b) Bag filter with multiple blocks: at least one filter element per block shall be sampled.
4.2.3 Sampling time and interval
The filter element shall first be sampled around one year after its operation starts. Thereafter, it is
preferable to sample at about one-year intervals.
A sample of the unused fabric filter shall be stored as reference to create a baseline for comparison.
Though plants installing a bag filter system usually operate continuously, the facility shall be shut down
when sampling the filter media. Therefore, it is preferable to sample the filter element during a routine
shut-down period of the facility, such as during periodic inspection and repair.
4.3 Procedure for sampling
4.3.1 General
Sampling of the filter element is carried out by replacing old and installing new filter elements in the
sequence described in 4.3.2 to 4.3.5.
4.3.2 Preparation
a) Stop the dust laden gas flow to the bag filter system, operate the system for more than 10 min with
clean air alone, and repeat pulse cleaning several times to remove dust from the filter element as
much as possible.
b) The flow rate and pressure drop across the filter element designated as a sample shall be measured.
c) Stop the clean air supply.
d) Then open the lid on the dirty side of the system and take a picture of the arrangement of the bag
filter from the bottom of the system.
4.3.3 Sampling of filter element
a) Open the lid on the clean side of the system.
b) Remove the retainer holding the filter element. Then remove the filter element by loosening the
snap rings used for fixing the element in place.
c) Pull down the sampled filter element to the dust bin with a rope while preventing penetration of
dust inside the filter medium and the re-entrainment of dust from the filter medium. Depending on
the situation, it may be pulled up to the clean side of the system. If this option is chosen, care shall
be taken not to contaminate the clean side of the system with dust from the removed filter.
NOTE 1 When filter element can be dropped down softly to the dust bin without a rope, the use of a rope
is not necessary.
d) Measure the mass of the filter element, if possible, and record the value in grams (g) for reference.
e) Put the sampled filter element into a polyethylene bag, etc. and seal the bag tightly. In order to
prevent changes in the properties of the filter, the bag should be kept under vacuum or filled with
an inert gas, if possible.
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ISO 22031:2021(E)

NOTE 2 This is to prevent absorption of moisture and re-entrainment of dust. Hence, it is desirable to put
the sampled filter element into a double layer polyethylene bag.
f) Record on the polyethylene bag details of the position of the sampled filter element in the filter
element array, including block number and position within the block. An example of the position of
the filter elements in the system is shown in Figure 2 (the hatched filter element location is 1-2-X).
NOTE 3 When a plan of the filter element array is provided, the location of the sampled filter element
should be marked on the plan.
Key
1 block number in the system X column number in the block (A to X)
2 row number in the block (1 to m)
Figure 2 — Arrangement plan of fabric elements in the bag
4.3.4 Installation of new fabric filters
Install new filter elements at the same positions in the same blocks as those where the sampled filter
elements have been removed.
4.3.5 Transportation of sampled filter elements to the test lab
The sampled filter elements shall be transported by the following process.
a) The polythene bags containing the sampled filter elements shall be put in a cardboard box not in
contact with each other and sealed tightly to prevent re-entrainment of attached dust, etc. In the
case of handling, care shall be taken that the dust does not re-entrain.
b) The sampled filter elements shall be sent by an appropriate means of transport to arrive at the test
laboratory within 2 days after sampling.
NOTE Each country has laws and regulations on the handling and transporting hazardous materials and
industrial wastes.
5 Test method for the sampled filter fabric
5.1 General
The sampled filter elements shall be selectively tested for the characteristics shown below after
negotiation between stakeholders. In the negotiation, consideration should be given to whether or not
the filter is damaged, and the degree of damage.
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ISO 22031:2021(E)

5.2 Appearance inspection
Stretch the filter fabric out on a flat plate, visually examine the damaged site, and measure the damage
outline size. The measured value should be recorded.
5.3 Photography
Mark the top (open) and bottom ends of the filter fabric with the filter stretched out; pictures of the
filter fabric should be taken from both front and back sides. In addition, if a photograph of the whole of
the filter fabric is considered difficult or unnecessary because of space restrictions at the photograph
site, or limited presence or absence of damage to the filter, etc., a partial photograph may be allowed.
5.4 Cutting out of the test specimen
Clean the filter fabric carefully in a manner appropriate for the test to be conducted, such as with a
vacuum cleaner, air jet, brush or scraper. The dust removed from the filter shall be captured and
preserved. Cut out test specimens from the filter that meet the following requirements.
Test samples shall be cut out at three sites designated as “upper”, “medium” and “lower” as shown in
Figure 3.
If it is judged that three sites are unnecessary because of limited presence, or absence, of damage on the
filter, a sample may be cut out at two sites such as “upper” and “lower”.
The samples shall be cut out where the filter contacts the retainer wire. The test specimen in the
longitudinal direction shall be cut so that the contact line of the longitudinal wire is located at the
centre of the specimen, and in the case of the lateral test specimen, the lateral contact line is located at
the centre. An example of this is shown in Figure 3.
5.5 Testing
5.5.1 General
Measurement of each of the test specimens shown in Figure 3 shall be as described in 5.5.2 to 5.5.6. In
cases where the test is performed on a dusty filter, the attached dust should be brushed away as much
as possible while preventing dust from being released to the environment.
5.5.2 Tensile strength
The test shall be performed in accordance with the method specified in ISO 16891:2016, 7.3.
Cut out three test specimens (25 mm × 200 mm) in both longitudinal and lateral directions from the
sample, pull each of them at a constant rate (100 mm/min) with a width of 25 mm and a clamp distance
of 100 mm, calculate the maximum load (N) and obtain an average value for both sets of measurements.
The measured data shall be recorded together with the test method.
5.5.3 Elongation ratio
The test shall be performed in accordance with the cut strip method in the method A specified in
ISO 16891:2016, 7.3.
Cut out three test specimens (25 mm × 200 mm) in longitudinal and lateral directions, respectively,
from the sample, pull each of them at a constant rate (100 mm/min) with a width of 25 mm and a
clamp distance of 100 mm, calculate the elongation ratio (%) and obtain an average value of them. The
measured data shall be recorded together with the test method.
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ISO 22031:2021(E)

5.5.4 Air permeability
The measurement shall be performed both with dust attached on the filter and with the dust removed
using a brush, a cleaner, etc. to a level that does not damage the fabric filter.
The test shall be performed according to Frazier type method specified in ISO 9237 or an equivalent
[13]-[15]
method . Take three test specimens from the sample and obtain their average permeability value
3 2 3 2
at the differential pressure specified in the referenced method. The unit is (cm /s)/cm or cm /cm /s.
The measured data shall be recorded together with the test method.
5.5.5 Observation with a microscope
Take enlarged photographs of the dust collecting surface, cross-section and cleaned surface of the filter
fabric using an optical microscope, confirm the presence or absence of dust leaks and record the result.
Optionally, take electron microscopic photographs to confirm the diameter and degradation condition
of the fibre and record the result.
5.5.6 Optional characteristics for measurement
a) Thickness of the filter medium
Measure the filter thickness at several points in the specimen with an appropriate measuring
device such as a dial gauge.
b) Stiffness of the filter medium
c) Cohesiveness of dust particles
d) Size distribution of dust particles
After dispersing the dust particles removed from the filter medium analyse their particle size
distribution with a particle size analyser such as a laser scattering instrument.
e) Chemical make-up of dust particles
Measure the chemical components of the dust particles remo
...