ISO 8504-5:2024

International
Standard
ISO 8504-5
First edition
Preparation of steel substrates
2024-09
before application of paints
and related products — Surface
preparation methods —
Part 5:
Water jet cleaning
Préparation des subjectiles d'acier avant application de peintures
et de produits assimilés — Méthodes de préparation des
subjectiles —
Partie 5: Nettoyage au jet
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Health and safety . 2
4.1 General requirements .2
5 Consideration of water jetting pressure and flow parameters . 2
5.1 General .2
5.2 Methods .2
5.2.1 General .2
5.2.2 Cleaning with low-pressure water (LP WC) .3
5.2.3 Cleaning with high-pressure water (HP WC) .3
5.2.4 Cleaning with high-pressure water jetting (HP WJ) .3
5.2.5 Cleaning with very high-pressure water jetting (VHP WJ) .3
5.2.6 Cleaning with ultra high-pressure water jetting (UHP WJ) .4
6 Components . 4
6.1 General .4
6.2 Pump . .5
6.3 Hose and fittings .5
6.4 Water path .5
6.5 Vacuum recovery .5
6.6 Water quality .5
6.7 Manual guns .5
6.8 Remote gun or wall-deck cleaning heads .5
6.9 Nozzle .6
6.10 Containment (management of water) .6
7 Systems . 6
7.1 Continuous system .6
7.2 Pulsed (disrupted) system .6
8 System operation . 6
8.1 General .6
8.2 Interactive parameters for productivity .7
8.3 Additives .7
8.4 Maintenance coating work .8
8.5 Maintenance of pump .8
8.6 Pressure drop in the hydraulic system .8
8.7 Positioning of the gun.8
9 Procedure . 8
9.1 Preparation before water jetting .8
9.2 During water jetting .8
9.2.1 Selection of initial condition .8
9.2.2 Selection of preparation grade .9
9.2.3 Selection of water jetting method .9
9.2.4 Selection of water jetting system .9
9.3 After water jetting and before applying coatings .9
10 A ssessment of the cleaned surface . 9
10.1 Selection of preparation grade .9
10.2 Field test .9
10.3 Organic contaminants . .10
10.4 Visual .10

iii
10.4.1 Visual assessment of preparation grade .10
10.4.2 Flash rust .10
10.5 Non-visible inorganics contaminants .10
10.6 Third-party representation .10
10.7 Conformity .10
Annex A (normative) Pressure levels .11
Annex B (informative) High-pressure /Ultra high-pressure water jetting: theoretical and
practical information .12
Annex C (informative) Flash rust guidance. 14
Bibliography .15

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
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 document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
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 35, Paints and varnishes, Subcommittee SC 12,
Preparation of steel substrates before application of paints and related products.
A list of all parts in the ISO 8504 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
Introduction
The performance of protective coatings of paint and related products applied to steel is significantly
affected by the state of the steel surface immediately prior to painting. The principal factors that are known
to influence this performance are:
— the presence of rust and mill scale,
— the presence of surface contaminants, including salts, dust, oils and greases, and
— the surface profile.
The ISO 8501 series, the ISO 8502 series and the ISO 8503 series provide methods for assessing these
factors, while the ISO 8504 series provides requirements and guidance on the preparation methods that
are available for cleaning steel substrates, indicating the capabilities of each in attaining specified levels of
cleanliness.
The ISO 8504 series is applicable to new and corroded steel surfaces and to steel surfaces that are uncoated
or have been previously coated with paints and related products.
The ISO 8501, ISO 8502, ISO 8503 and ISO 8504 series do not contain provisions for the protective coating
system to be applied to the steel surface. They do not contain provisions for the surface quality requirements
for specific situations, even though surface quality can have a direct influence on the choice of protective
coating to be applied and on its performance. Such provisions can be found in other documents such as
national standards and codes of practice. Users of the ISO 8501, ISO 8502, ISO 8503 and ISO 8504 series
should ensure the qualities specified are:
— compatible and appropriate both for the environmental conditions to which the steel will be exposed
and for the protective coating system to be used, and
— within the capability of the cleaning procedure specified.
The primary objective of surface preparation is to ensure the removal of deleterious matter and to obtain
a surface that permits satisfactory adhesion of the priming paint to steel. It is also intended to assist in
reducing the amounts of contaminants that initiate corrosion.
Water jetting is an effective method for removing coatings from previously painted surfaces, removing
water-soluble contaminants, and producing partially removed coatings. While water jetting by itself can
produce a granular profile in metals under some conditions, water jetting is considered a secondary surface
preparation method and is not used to provide the primary anchor pattern on the metallic substrate known
as “surface profile.” Water jetting is primarily used for surfaces where there is an adequate pre-existing
surface profile or for Grade C and Grade D substrates. Water jetting can remove oil, grease, and corrosion-
stimulating substances such as chlorides and sulphates. Water jetting is widely applicable because this
method of surface preparation has several features listed below.
— The method allows a high production rate.
— Coatings and salts can be removed in one pass.
— Production rates can be similar to conventional abrasive blast cleaning.
— A work atmosphere is present without particulate dust pollution.
— Other trades can work nearby during the surface preparation.
— Surface preparation can generally be performed in unsafe explosive or flammable areas without
interruption with suitable control measures, for example, earthing of equipment to prevent static
discharges from water jetting guns, pumps, and hoses.
— The equipment can be stationary or mobile and is adaptable to the objects to be cleaned.
— The equipment can be remotely or manually controlled.

vi
— The method is applicable to most types and forms of metal surfaces.
— Different surface preparation grades can be produced.
— It is possible to remove selectively partial failed coatings to leave sound coatings intact.
Representative photographic examples in ISO 8501-4:2020, Clause 8 can be used for assessing some new
and previously coated steel surfaces. Owing to the many different situations that arise in the preparation
of surfaces, these photographs are not always sufficient to describe specific instances. It is therefore
recommended to produce specific photographs of a treated reference area that are acceptable to the
interested parties for use as a basis for further surface preparation procedures.

vii
International Standard ISO 8504-5:2024(en)
Preparation of steel substrates before application of paints
and related products — Surface preparation methods —
Part 5:
Water jet cleaning
1 Scope
This document specifies water jet cleaning methods for the removal of the existing coatings and rust
during surface preparation of steel surfaces before application of paints and related products. It provides
information on the effectiveness of the individual methods and their fields of application. It also describes
the equipment and the procedures to follow.
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 4628-3, Paints and varnishes — Evaluation of degradation of coatings — Designation of quantity and size of
defects, and of intensity of uniform changes in appearance — Part 3: Assessment of degree of rusting
ISO 8501-4:2020, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 4: Initial surface conditions, preparation grades and flash rust grades
in connection with water jetting
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
field test
cleaning of selected surfaces, carried out before the start of work, intended to achieve the specified
preparation grades
Note 1 to entry: ISO 8501-4:2020, Clause 5 defines the preparation grades that should be obtained through the field test.
Note 2 to entry: The field test can be referred to as the control specimen.
3.2
flash rust
rapid rusting of the surface prepared by water jet or water-abrasive blast cleaning, which occurs as the
substrate is drying
Note 1 to entry: ISO 8501-4:2020, Clause 6 defines the flash rust grades.
Note 2 to entry: Flash rust in this document is more limited than the definition given in ISO 4618:2023, 3.120.

3.3
nozzle
device that modifies the stream of water as it discharges from the system
Note 1 to entry: Nozzle openings can be referred to as bits, tips, or orifices.
3.4
threshold pressure
minimum pressure required to penetrate the material
3.5
water jetting
continuous or discontinuous stream of water in air with defined geometry, velocity and, if discontinuous,
frequency
[SOURCE: ISO/TS 19392-3:2018, 3.1]
4 Health and safety
4.1 General requirements
The procedures described in this document shall be carried out by either suitably trained or supervised
personnel or both. The substances and procedures used in these methods can be injurious to health
if adequate precautions are not taken. Attention is drawn in the text to certain specific hazards. This
document refers only to the technical suitability of the methods and does not absolve the user from statutory
obligations relating to health and safety.
WARNING — Equipment and materials used for surface preparation can be hazardous. It is important
to ensure that adequate instructions are given and that all required precautions are exercised. Only
trained or certified operatives or both should use the equipment.
5 Consideration of water jetting pressure and flow parameters
5.1 General
The contract documents describe the final condition of the substrate. Depending on the initial condition of
the area and the materials intended to be cleaned, the method to achieve the preparation grades described
in ISO 8501-4 can be low-pressure, high-pressure, or ultra high-pressure methods. The methods of water
cleaning or water jetting are based on the capabilities of the equipment and its components. Dwell time,
traverse rate, pressure, flow, stand-off distances, the number of nozzles, and rotational speed all interact
in determining what material remains and what will be removed. Removal of loose material such as dirt,
detritus, or bird faeces, which is an example of the preparation grade Wa 1, requires different equipment
than the stripping of a coating system which is an example of the preparation grade Wa 2 1/2. Cleaning to a
preparation grade of Wa 1 requires a different set of parameters than cleaning to a preparation grade of Wa
2 1/2. See ISO 8501-4:2020, Clause 5 for definitions of Wa preparation grades.
Pressurized water cleans by hydraulic shear (mass) at the lower pressures, and by implosion or cavitation
at the upper pressures or both. The removal of material by mass or implosion is a continuum, not a discrete,
abrupt change. This mix is discussed in greater depth in Annex B.
5.2 Methods
5.2.1 General
It is important to carefully consider the historic concept of linking the pressure and flow to material
removal. The operating parameters specified in Table A.1 shall apply. Ultra high-pressure water jetting
can accomplish all of these end results by changing the stand-off distance and traverse time, but it is not
economical to use ultra high-pressure water jetting, for purposes such as removing loose dirt or achieving

the preparation grade Wa 1. Low-pressure water cleaning cannot deliver the energy density, expressed as
kJ/mm , or threshold pressure to the surface to break the cohesion force of old rust or coating systems.
Contractors use the pump and flow conditions which are most economical to achieve the desired result.
Pressurized water cleaning is accomplished when droplets of water impact the substrate. The droplets force
their way into pits and crevices and hydraulically shear between the interface of the metal and the corrosion
or paint layers. Water jetting (water jet cleaning or water jet stripping) uses cavitation or implosion to cut
through the different layers of coating or corrosion.
5.2.2 Cleaning with low-pressure water (LP WC)
Low-pressure water cleaning is performed at pressures less than 34 MPa. The stream of water jetting shears
the surface with the load parallel to the surface. The predominant energy characteristic is the mass.
Low-pressure water cleaning depends upon the mass flow of the water stream to remove coatings by
shearing between the substrate and the material to be removed. The achieved result is removal of loose dirt,
grime, bird droppings, some of the soluble contaminants and possibly weathered paint or chalk. The stream
flows parallel to the substrate, so it is possible that the water stream does not get into pits and crevices.
A typical usage is to wash surfaces which are intended to be cleaned by abrasive blast or a hand or power
tool before starting that method. LP WC is typically conducted with a fan jet or non-rotating multi-orifice
nozzle. When a multiple orifice nozzle is rotated, it produces a flexure stressing by a repetitive loading and
unloading of the coatings system as the stream passes over the surface. The rapid load and unloading reveals
areas of low adherence and other nonvisible defects in the coating system.
5.2.3 Cleaning with high-pressure water (HP WC)
Water cleaning which is performed at pressures from 34 MPa to 70 MPa combines shear and implosion
to remove unwanted material. The predominate energy characteristic is a combination of the mass and
velocity.
High-pressure water cleaning depends upon a combination of the mass flow of the water stream and the
impact energy to remove coatings by predominately shearing between the substrate and the material to
be removed with subordinate impact and implosion. The result is the partial removal of adhered coatings,
revelation of incipient blisters or areas of low adhesion, and partial removal of rust layers. Oxidized paint
is removed from the adherent layer. The water stream can get into the pits and craters and crevices. In
removal of old rust, the typical appearance is clean, shiny pits with adherent rust layers at the top surface. It
is the opposite visual appearance of a dry abrasive blast method where the shiny top is cleaned, and the pits
are filled with dark, detrital material.
5.2.4 Cleaning with high-pressure water jetting (HP WJ)
Water cleaning which is performed by pressurized water jetting between 70 MPa and 140 MPa is considered
high-pressure water jetting by some industries.
At 70 MPa, the effect of the energy density starts to predominate over the shear forces of the mass flow as
the velocity of the water stream increases through a smaller diameter tip.
High-pressure water cleaning depends upon a combination of the mass flow of the water stream and the
energy density, in order to remove coatings by predominately impact and implosion and by subordinately
shearing between the substrate and the material to be removed. The achieved result is the removal of
adhered coatings with lower cohesion, removal of coatings over areas of low adhesion or incipient blisters,
and partial to full removal of rust layers.
5.2.5 Cleaning with very high-pressure water jetting (VHP WJ)
Water cleaning which is performed by pressurized water jetting between 140 MPa and 210 MPa removes
material predominately by implosion.

Systems operating greater than 140 MPa clean predominately by impact implosion perpendicular to the
surface, resulting in the sharp cut where the jet impacts the surface. The predominant energy characteristic
is velocity.
The cleaning mechanism is a combination of shear and energy density. The side shear (mass flow) becomes
less predominant as the energy density increases, and the stand-off distance becomes more critical. The
jetter requires more experience and training to maintain a narrow stand-off distance and guide the sharp
cut-off edge. The use of >140 MPa is suitable to economically achieve preparation grades Wa 2 or Wa 2 1/2,
depending on the coating and rust. See ISO 8501-4:2020 Clause 5 for descriptions of preparation grades.
NOTE VHP WJ is referred to as THP WJ (see Reference [3]).
5.2.6 Cleaning with ultra high-pressure water jetting (UHP WJ)
Water cleaning which is performed by pressurized water jetting greater than 210 MPa removes material
predominately by implosion.
Ultra high-pressure water jetting is typically used to achieve preparation grades Wa 2 1/2 and Wa 3 to
bare substrate. The cleaning action is caused by impact intensity, which is an implosion or cavitation of the
individual droplets on the substrate. The cleaning is a straight cut through the material yielding a sharp
edge. The pressured water is heated by the compression and rapidly vaporizes off the surface. The drying
time is fast compared to de-energized water in low-pressure or high-pressure water systems. The stripping
of coatings with none to light flash rusting can be achieved and held with a full recovery vacuum system.
This recovery vacuum system prevents water mist from subsequent, near-by activities from settling on the
previously prepared Wa substrates.
The threshold pressure of the target substrate is crucial when the objective is to remove existing coatings or
corrosion and to not significantly change the texture or profile.
6 Components
6.1 General
A wide variety of pumps and delivery systems are used for water je
...