ISO/TS 16688:2017
(Main)Guidelines for the selection of coating types, tests and methods of assessing the performance of coated aluminium in architectural applications
Guidelines for the selection of coating types, tests and methods of assessing the performance of coated aluminium in architectural applications
ISO/TS 16688:2017 establishes a system to select coating types for architectural applications depending on environment. It gives guidelines for the selection of tests and methods of measuring performance in terms that are of direct interest to the building designer. ISO/TS 16688:2017 is applicable to organic and anodic oxidation (AAO) coatings on aluminium, including those produced from liquid and powder paints, and combined coatings of organic and anodic oxidation coatings. It is designed to be applicable to novel coatings developed in the future.
Lignes directrices pour la sélection des types de revêtements, essais et méthodes d’évaluation des performances de l’aluminium revêtu dans les applications architecturales
General Information
Standards Content (Sample)
TECHNICAL ISO/TS
SPECIFICATION 16688
First edition
2017-11
Guidelines for the selection of coating
types, tests and methods of assessing
the performance of coated aluminium
in architectural applications
Lignes directrices pour la sélection des types de revêtements, essais et
méthodes d’évaluation des performances de l’aluminium revêtu dans
les applications architecturales
Reference number
ISO/TS 16688:2017(E)
©
ISO 2017
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ISO/TS 16688:2017(E)
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ISO/TS 16688:2017(E)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General . 3
4.1 Selection of methods to protect metals against corrosion . 3
4.2 System for selecting coating types for architectural applications . 3
5 Types of environment . 4
6 Classification of coatings . 7
6.1 Specifications for coated aluminium products . 7
6.2 Descriptions of coatings and coating processes . 8
6.3 Classifications of anodic oxidation coatings . 8
6.4 Classifications of paint coatings . 9
6.5 Classifications of combined coatings .10
6.6 Comparison of the classifications .10
7 Coating selection for different environments .10
8 Durability tests .12
8.1 General .12
8.2 Mechanical durability .12
8.2.1 General.12
8.2.2 Deformation .12
8.2.3 Indentation (hardness) .14
8.2.4 Abrasive and adhesive wear .15
8.2.5 Erosion.15
8.3 Chemical durability .16
8.3.1 General.16
8.3.2 Immersion tests .16
8.3.3 Spot and ring tests .19
8.3.4 Poultice or pat tests .20
8.3.5 Tests using an absorbent medium .20
8.3.6 Spray tests .20
8.3.7 Tests involving exposure to vapours or gases .21
8.4 Radiation and heat resistance .21
8.5 Weathering resistance .23
8.5.1 Resistance to artificial weathering .23
8.5.2 Resistance to natural weathering .23
9 Selection of test methods to enable the comparison of different coating types for
service in different environments .23
10 Methods of measuring performance .25
10.1 General .25
10.2 Appearance .26
10.2.1 Visible defects . .26
10.2.2 Colour .26
10.2.3 Reflectance .27
10.3 Coating integrity .28
10.3.1 Loss of adhesion or cohesion .28
10.3.2 Loss of coating thickness .28
10.3.3 Loss of coating mass or density .29
10.3.4 Change of electrical resistance .29
10.3.5 Increase in absorptivity .30
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ISO/TS 16688:2017(E)
Annex A (informative) Recommended cleaning procedures for coated aluminium
architectural materials .31
Bibliography .32
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ISO/TS 16688:2017(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
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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
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URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 79, Light metals and their alloys,
Subcommittee SC 2, Organic and anodic oxidation coatings on aluminium.
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TECHNICAL SPECIFICATION ISO/TS 16688:2017(E)
Guidelines for the selection of coating types, tests
and methods of assessing the performance of coated
aluminium in architectural applications
1 Scope
This document establishes a system to select coating types for architectural applications depending
on environment. It gives guidelines for the selection of tests and methods of measuring performance in
terms that are of direct interest to the building designer.
This document is applicable to organic and anodic oxidation (AAO) coatings on aluminium, including
those produced from liquid and powder paints, and combined coatings of organic and anodic oxidation
coatings. It is designed to be applicable to novel coatings developed in the future.
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 7583, Anodizing of aluminium and its alloys — Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7583 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http://www.electropedia.org/
— ISO Online browsing platform: available at http://www.iso.org/obp
3.1
abrasive wear
wear process of a material caused by cutting or scratching actions of hard bodies or hard particles
[SOURCE: ISO 4378-2:2017, 3.3.1.2]
3.2
adhesive wear
wear process due to adhesion and extraction of material out of the body surface
[SOURCE: ISO 4378-2:2017, 3.3.1.3]
3.3
accelerated test
test undertaken under conditions designed to speed material deterioration
[SOURCE: ISO 23936-2:2011, 3.1.1]
3.4
architectural applications
external and internal building applications for coated aluminium products where both appearance and
long life are important
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ISO/TS 16688:2017(E)
3.5
coating
covering on a substrate, which has protective, decorative or specific technical properties
3.6
coil coating
coating process whereby the coating material is applied continuously to a coil of metal which may be
rewound after the film has dried
[SOURCE: ISO 4618:2014, 2.56]
3.7
designer
person or organization responsible for stating the form and specification of a building or parts of a
building
3.8
durability
ability of a coating to withstand fabrication and installation procedures and a service environment
without excessive degradation of the decorative and other specific properties of the finish
3.9
inorganic coating
coating (3.5) of a coated product consisting primarily of inorganic, non-metallic material
3.10
organic coating
coating (3.5) of a coated product consisting primarily of organic material
3.11
paint
liquid or powder containing pigments, which, when applied to a substrate, forms a film having
protective, decorative or specific technical properties
[SOURCE: ISO 4618:2014, 2.184, modified — The definition has been changed so that it is restricted to
liquid and powder coating materials and not to opaque films.]
3.12
simulation
use of a similar or equivalent system to imitate a real system so that it behaves like or appears to be the
real system
[SOURCE: ISO 16781:2013, 2.9]
3.13
sol-gel processing
conversion of a chemical solution or colloidal suspension (sol) to an integrated network (gel) which can
then be further densified
[SOURCE: ISO/TS 80004-8:2013, 6.4.5]
3.14
time-of-wetness
period during which a surface is covered by adsorptive and/or liquid films of aqueous solution
[SOURCE: ISO 9223:2012, 3.5, modified — The definition has been generalized so as not to be specific to
metals and corrosion.]
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ISO/TS 16688:2017(E)
3.15
underfilm corrosion
corrosion of a metal surface taking place beneath a coating
EXAMPLE Filiform corrosion and the corrosion that can occur beneath blistering.
3.16
visible defect
unacceptable physical imperfection or flaw in the surface coating detracting from the specified
reference material or from the product’s functions
[SOURCE: ISO 16348:2003, 2.4]
4 General
4.1 Selection of methods to protect metals against corrosion
ISO 11303:2002 gives guidelines for the selection of methods of protection against the atmospheric
corrosion of metals and alloys. It is applicable for technical equipment and products made of structural
metals, including aluminium alloys, and used under atmospheric conditions. It identifies the main
considerations in the decision-making process:
— the structural metal;
— the design of the structural element;
— the active agent, e.g. chloride ions;
— the condition of action, e.g. ambient temperature.
It uses the atmospheric corrosion classification of ISO 9223:2012. The principal factor in the selection
process is the service life of the component or product, which is derived in relation to its most important
functional property, e.g. colour.
This document is concerned with aluminium alloys as the structural metal, although it gives no
guidance on alloy selection. The design of the structural element is also outside its scope. It is concerned
with the selection of coatings depending on the active agents and conditions of action in atmospheric
environments with regard to functional properties. However, it includes no quantitative information
that relates the quality degree of the coating to service life. ISO 15686-1 gives general principles of
service life planning.
4.2 System for selecting coating types for architectural applications
With reference to the guidelines of ISO 11303:2002, the following steps can be followed to select a
coating type for a specific architectural application.
— Identify active agents and conditions of activity of the environment.
— Rate the intensity of the agents. Clause 5 provides guidance for the main agents: acidic pollution, UV
(ultra-violet) radiation and chloride deposition.
— Weigh the contributions of the agents according to the conditions of activity, e.g. time-of-wetness,
ambient temperature, wet/dry cycling frequency, the frequency of cleaning or washing by rain.
— Using the information of Clause 7, select the coating types most likely to be suitable. Refer to the
specifications for coated aluminium listed in Clause 6 for more information on specific coatings.
— Eliminate any coatings on the basis of other factors such as requirements for the design of the
structural elements including colour and reflectivity, and costs.
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ISO/TS 16688:2017(E)
— Undertake comparative tests to identify the coatings most suitable for the service environment. Tests
and methods of measuring performance are described in Clauses 8 and 10, while the applicability of
tests for different environments is covered in Clause 9.
5 Types of environment
A main function of the coating is to preserve the original appearance of the coated product. Thus, the
coating should not degrade so that it becomes unsightly. An example is the effect of UV radiation on
organic coatings and dyed AAO coatings, which can cause a change in appearance. Furthermore, the
coating should prevent the corrosion of the aluminium substrate. Thus, degradation of the coating, even
if it is not noticeable, can be the precursor to aluminium corrosion which can affect the appearance of
the product. Note that EN 1999-1-1:2007+A1, Eurocode 9, gives basic design rules to avoid loss of load-
bearing capacity due to corrosion for buildings and structures made of wrought aluminium alloys.
ISO 9223:2012 gives six classes of outdoor and indoor environments based on corrosivity alone.
ISO 12944-2:1998 includes the same categories but adds further examples. Table 1 gives those
categories and includes descriptions from both those standards.
The corrosivity categories of ISO 9223:2012 are defined by the first-year corrosion effects on standard
specimens of uncoated aluminium, carbon steel, zinc and copper, which are assessed in terms of the most
significant atmospheric agents influencing the corrosion of the metals and alloys. The agents considered
were the time-of-wetness, and sulfur dioxide (SO ) and chloride pollution levels. The standard includes
2
data defining different levels of exposure to these agents. The levels of time-of-wetness extend from not
more than 10 hours per year to more than 5 500 hours per year. The levels of SO deposition rate extend
2
2 2
from not more than 4 mg/(m ·d) to more than 200 mg/(m ·d). The levels of chloride deposition rate
2 2
extend from not more than 3 mg/(m ·d) to more than 300 mg/(m ·d). ISO 9223:2012 also includes data
for other important pollutants although they are not used as classification criteria.
ISO 12944-2:1998 is concerned with painted steel structures.
For the purposes of this document, the categorization of ISO 9223:2012 has certain deficiencies as
follows.
— It is based on the corrosion of uncoated metals.
— It does not fully differentiate the effect of chloride ions from other pollutants.
— It does not include acidic pollutants other than sulfur dioxide.
— It does not consider climatic variations in UV radiation.
A significant factor affecting the corrosion of some metals and particularly steel is the chloride content
of the environment. The main sources of chlorides are the sea and de-icing of roads. Airborne salinity is
strongly dependent on the variables influencing the transport inland of sea-salt, such as wind direction,
wind velocity, local topography and distance of the exposure site from the sea. Surfaces that are
sheltered and not rain-washed in marine atmospheres where chlorides are deposited and accumulated
can experience a higher corrosivity due to the presence of hygroscopic salts. Aluminium is much less
affected by chlorides than steel, unless there is associated acidity or alkalinity.
The corrosivity of an atmosphere towards metals is not necessarily comparable to its severity in
promoting the degradation of non-metallic coatings, which can affect the aesthetic properties of the
product. However, coatings can be degraded by acids and alkalis, and associated time-of-wetness. The
wetting of surfaces is caused by many factors, for example, dew, rainfall, melting snow, a high humidity
level and condensation. Chemicals from the atmosphere can dissolve in surface films of water and
become more concentrated as the water evaporates. Thus, although time-of-wetness is important, so is
wet/dry cycling. Particulates on a surface can absorb water creating a poultice with persistent wetness
depending on rain washing and drying.
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ISO/TS 16688:2017(E)
Table 1 — Typical environments related to corrosivity categories
Corrosivity
Corrosivity Outdoor Indoor
category
C1 Very low Dry- or cold-zone atmospheric Heated spaces with low relative
environment with very low pollution and humidity (RH) and insignificant
time-of-wetness. pollution.
EXAMPLE Certain deserts, central EXAMPLE Offices, shops, schools,
Arctic/Antarctica. hotels, museums.
C2 Low Temperate-zone atmospheric Unheated spaces with varying
environment with low pollution. temperature and RH. Low frequency of
condensation and low pollution.
EXAMPLE Rural areas, small towns.
EXAMPLE Depots, sports halls.
Dry- or cold-zone atmospheric
environment with short time-of-wetness.
EXAMPLE Deserts, subarctic areas.
C3 Medium Temperate-zone atmospheric Spaces with moderate frequency of
environment with medium pollution or condensation and moderate pollution
some effect of chlorides. from production processes.
EXAMPLE Urban areas, coastal areas EXAMPLE Food-processing plants,
with low deposition of chlorides. laundries, breweries, dairies.
Subtropical- and tropical-zone
atmosphere with low pollution.
C4 High Temperate-zone atmospheric Spaces with high frequency of
environment with high pollution or condensation and high pollution from
substantial effect of chlorides. production processes.
EXAMPLE Polluted urban areas, EXAMPLE Chemical plants, swimming
industrial areas, coastal areas without pools, coastal ship and boatyards.
spray of salt water or exposure to strong
effect of de-icing salts.
Subtropical-zone and tropical-zone
atmosphere with medium pollution.
C5 Very high Temperate- and subtropical-zone at- Spaces with very high frequency of
mospheric environment with very high condensation and/or with high pollution
pollution and/or significant effect of from production processes.
chlorides.
EXAMPLE Mines, caverns for
EXAMPLE Industrial areas, coastal industrial purposes, unventilated
areas, sheltered position on coastline. sheds in subtropical and tropical zones.
CX Extreme Subtropical- and tropical-zone (very high Spaces with almost permanent conden-
time-of-wetness) atmospheric environ- sation or extensive periods of exposure
ment with very high pollution including to extreme humidity effects and/or
accompanying and production factors with high pollution from production
and/or strong effect of chlorides. processes.
EXAMPLE Extreme industrial areas, EXAMPLE Unventilated sheds in
coastal and offshore areas, occasional humid tropical zones with penetration
contact with salt spray. of outdoor pollution including airborne
chlorides and corrosion-stimulating
particulate matter.
The degradation of organic coatings is not only dependent on the amount of UV exposure but also
the presence of water and oxygen. Whereas atmospheric oxygen levels may not be expected to vary
significantly; time-of wetness as determined by the ambient temperature and relative humidity (RH)
can have an important effect on degradation due to UV radiation. Inorganic materials are generally
unaffected by UV radiation.
Inorganic materials can be degraded by the presence of water, particularly as an aqueous solution of
an aggressive chemical. Considering acidic pollutants, the main sources of sulfur dioxide are emissions
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ISO/TS 16688:2017(E)
from industrial plants using coal or oil. Traffic is the main source of nitrogen dioxide emissions. High
levels of nitric acid are associated with high concentrations of nitrogen dioxide, organic compounds
and UV light. The decreasing sulfur dioxide levels in many parts of the world and the elevated levels of
nitrogen oxides caused by increasing traffic, together with ozone and particulates, has created a new
multi-pollutant environmental situation. In other parts of the world, in relation to the rapid development
of industry, the corrosive effect of sulfur dioxide pollution is intensifying and still dominating. Ozone is
formed in the atmosphere by interactions between sunlight, oxygen and pollutants. The concentrations
are higher in polluted rural atmospheres and lower in high-traffic urban areas. Particulates including
aerosols arise from high-concentration traffic areas and industrial activities. They can contain high
concentrations of corrosion-active components such as sulfate, nitrate and chloride anions. The burning
of coal and wood is a major source of soot. There is also diesel soot from road vehicles.
EN 1396:2015 has certain advantages over ISO 9223:2012. It is concerned with painted aluminium and
consequently categorizes end-use environments according to UV radiation intensity, as well as potential
corrosivity (see Table 2). The indices are defined in terms of the performance of variously coated test
panels during outdoor exposure testing carried out in compliance with EN 13523-19 and evaluated
according to EN 13523-21. UV radiation indices correspond to colour change and retained gloss over
two years of outdoor exposure. Corrosivity indices correspond to specific amounts of underfilm
corrosion after specific times of outdoor exposure rather than rate data for uniform corrosion as used
by ISO 9223:2012.
Table 2 — Corrosivity and UV radiation indices for different environments (EN 1396:2015)
UV radiation
Environment Corrosivity index
index (R )
uv
High UV radiation with severe conditions 3 4
Tropical (high temperature, high humidity) outdoor areas
High UV radiation outdoor areas 2
...
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