SIST EN ISO 16784-1:2025

SLOVENSKI STANDARD
01-marec-2025
Korozija kovin in zlitin - Korozija in obraščanje v industrijskih vodnih hladilnih
sistemih - 1. del: Smernice za izvajanje vrednotenja pilotne serije aditivov za
kontrolo korozije in obraščanja pri odprtih obtočnih hladilnih vodnih sistemih (ISO
16784-1:2024)
Corrosion of metals and alloys - Corrosion and fouling in industrial cooling water systems
- Part 1: Guidelines for conducting pilot-scale evaluation of corrosion and fouling control
additives for open recirculating cooling water systems (ISO 16784-1:2024)
Korrosion von Metallen und Legierungen - Korrosion und Fouling in industriellen
Kühlwassersystemen - Teil 1: Leitfaden für die Bewertung von Zusatzstoffen gegen
Korrosion und Fouling in offenen Kühlwasserrezirkulationssystemen (ISO 16784-1:2024)
Corrosion des métaux et alliages - Corrosion et entartrage des circuits de
refroidissement à eau industriels - Partie 1: Lignes directrices pour l'évaluation pilote des
additifs anticorrosion et antitartre pour circuits de refroidissement à eau à recirculation
ouverts (ISO 16784-1:2024)
Ta slovenski standard je istoveten z: EN ISO 16784-1:2024
ICS:
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 16784-1
EUROPEAN STANDARD
NORME EUROPÉENNE
December 2024
EUROPÄISCHE NORM
ICS 77.060 Supersedes EN ISO 16784-1:2008
English Version
Corrosion of metals and alloys - Corrosion and fouling in
industrial cooling water systems - Part 1: Guidelines and
requirements for conducting pilot-scale evaluation of
corrosion and fouling control additives for open
recirculating cooling water systems (ISO 16784-1:2024)
Corrosion des métaux et alliages - Corrosion et Korrosion von Metallen und Legierungen - Korrosion
encrassement des circuits de refroidissement à eau und Fouling in industriellen Kühlwassersystemen - Teil
industriels - Partie 1: Lignes directrices et exigences 1: Leitfaden für die Bewertung von Zusatzstoffen gegen
pour l'évaluation pilote des additifs anti-corrosion et Korrosion und Fouling in offenen
anti-encrassement pour circuits de refroidissement à Kühlwasserrezirkulationssystemen (ISO 16784-
eau à recirculation ouverts (ISO 16784-1:2024) 1:2024)
This European Standard was approved by CEN on 17 October 2024.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 16784-1:2024 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 16784-1:2024) has been prepared by Technical Committee ISO/TC 156
"Corrosion of metals and alloys" in collaboration with Technical Committee CEN/TC 262 “Metallic and
other inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys”
the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by June 2025, and conflicting national standards shall be
withdrawn at the latest by June 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 16784-1:2008.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 16784-1:2024 has been approved by CEN as EN ISO 16784-1:2024 without any
modification.
International
Standard
ISO 16784-1
Second edition
Corrosion of metals and alloys —
2024-12
Corrosion and fouling in industrial
cooling water systems —
Part 1:
Guidelines and requirements for
conducting pilot-scale evaluation
of corrosion and fouling control
additives for open recirculating
cooling water systems
Corrosion des métaux et alliages — Corrosion et encrassement
des circuits de refroidissement à eau industriels —
Partie 1: Lignes directrices et exigences pour l'évaluation pilote
des additifs anti-corrosion et anti-encrassement pour circuits de
refroidissement à eau à recirculation ouverts
Reference number
ISO 16784-1:2024(en) © ISO 2024

ISO 16784-1:2024(en)
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
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or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 16784-1:2024(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General requirements and recommendations. 2
4.1 Selection of test methods .2
4.1.1 Laboratory and off-site testing .2
4.1.2 On‑site testing.2
4.1.3 Online testing .2
4.2 Cost analysis .2
5 Test unit design parameters . 2
5.1 General .2
5.2 Construction materials .3
5.2.1 Cooling towers .3
5.2.2 Film fill .3
5.2.3 Non-heat-transfer metal surfaces .4
5.2.4 Heat exchangers .4
5.3 Measuring instrument .4
5.4 Other simulation devices .5
6 Operating parameters . 5
6.1 General .5
6.2 Surface temperature .5
6.3 Water velocity .5
6.4 Residence time .5
7 Water quality and contamination. 6
7.1 General .6
7.2 Natural versus synthetic water supplies .6
7.3 Water from different sources .6
7.3.1 Fresh water .6
7.3.2 Seawater and brackish water . .6
7.3.3 Recycle/reuse water .7
7.3.4 Dual and combined make-up systems.7
7.4 Contamination .7
7.4.1 General .7
7.4.2 Process leaks .7
7.4.3 Biological matter .7
7.4.4 Airborne solids and gases .7
8 Parameters to be evaluated in pilot test units . 8
8.1 Corrosion .8
8.1.1 General .8
8.1.2 Criteria for corrosion evaluations .8
8.1.3 Types of corrosion damage .8
8.1.4 Microbiologically influenced corrosion .8
8.1.5 Methods for evaluating corrosion in pilot-scale test units .8
8.2 Fouling .9
8.2.1 General comment .9
8.2.2 Types of water-side fouling .9
8.2.3 Pilot-scale methods for evaluating fouling (see also ISO 16784-2) .9
8.3 Water treatment additives .10
8.3.1 Combination testing .10
8.3.2 Compatibility of additives .10

iii
ISO 16784-1:2024(en)
9 Design of pilot-scale performance testing facilities .10
9.1 Objectives .10
9.2 The importance of simulating specific process and application environments .10
9.3 Compromises in pilot-scale performance testing .11
9.3.1 Heat source, heat duty and temperature .11
9.3.2 Water chemistry .11
10 Pilot-scale facility operations .12
10.1 Documentation of design . 12
10.1.1 General comments . 12
10.1.2 Equipment . 12
10.1.3 Water treatment . 12
10.2 Repeatability of results and comparison with field performance . 13
10.3 Record-keeping and reports . 13
Annex A (informative) Selection of circulating cooling water treatment method . 14
Bibliography .15

iv
ISO 16784-1:2024(en)
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 156, Corrosion of metals and alloys, in
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 262,
Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of metals and
alloys, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 16784-1:2006), which has been technically
revised.
The main changes are as follows:
— the Introduction has been modified;
— normative references have been added;
— Clause 3 has been modified;
— Clause 4 has been modified: the title was changed from "Types of testing" to "General requirements and
recommendations" and the latest requirements on environmental protection have been added;
— Clauses 7 and 8 have been combined and content related to new water treatment methods has been added.
— the Bibliography has been modified.
A list of all parts in the ISO 16784 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
ISO 16784-1:2024(en)
Introduction
A lot of changes have taken place in the development environment of global industrial enterprises, including
advances in related technologies. As the industry grows and competition intensifies, while at the same time
more stringent pollution requirements are introduced and water becomes more scarce, businesses have
to operate in a safer, greener and more economical way. In many cases, cooling water quality is declining,
which leads to higher concentration rates, more corrosion and more susceptibility to scaling.
Cooling water treatment technologies have developed and their use is expanding. Water pollution caused
by additives used in cooling system has attracted public attention, and green environmental protection
additives have become a new trend in development. Factories need to achieve zero waste water discharge.
Cooling water treatments are effective measures for maintaining the best operating efficiency, protect the
economic life of equipment, suppress corrosion and prevent scaling, microbial pollution and deposition on
various heat transfer surfaces.

vi
International Standard ISO 16784-1:2024(en)
Corrosion of metals and alloys — Corrosion and fouling in
industrial cooling water systems —
Part 1:
Guidelines and requirements for conducting pilot-scale
evaluation of corrosion and fouling control additives for open
recirculating cooling water systems
1 Scope
This document specifies general requirements and parameters for the pilot test evaluation of corrosion and
scaling control additives in open recirculating cooling water systems. This document covers parameters
including test unit design, operation, water quality and contamination. It also covers the design and
operation of pilot test devices as well as parameters to be evaluated in pilot test units.
This document covers the criteria that are used in pilot scale testing programmes for selecting water
treatment programmes for specific recirculating cooling water systems.
This document is only applicable to open recirculating cooling water systems. It does not apply to closed
cooling systems and once-through cooling water systems.
This document applies only to systems that incorporate shell and tube heat exchangers with standard
uncoated smooth tubes and cooling water on the tube side. This document does not apply to heat exchangers
with shell-side water, plate and frame and/or spiral heat exchangers and other heat exchange devices.
However, when the test conditions are properly set up to model the surface temperature and shear stress in
more complex heat transfer devices, the test results can predict the results of operating heat exchangers of
that design.
The test criteria established in this document are not intended to govern the type of bench and pilot scale
testing normally carried out by water treatment companies as part of their proprietary product development
programmes. However, water treatment companies can choose to use the criteria in this document as
guidelines in the development of their own product development test procedures.
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 8044, Corrosion of metals and alloys — Basic terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 8044 and the following 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/

ISO 16784-1:2024(en)
3.1
fouling
deposition of any material on a heat transfer surface
3.2
surface-to-volume ratio
S/V ratio
ratio of the total surface area of metal exposed to water in the cooling system to the total volume of water in
the system
4 General requirements and recommendations
4.1 Selection of test methods
4.1.1 Laboratory and off-site testing
Laboratory testing, or testing at alternative off-site locations, can in some cases be necessary for selecting
cooling water chemical treatment programmes. This type of testing can be used for new construction
start-up programmes, when operating systems are not available, or for evaluating alternative treatment
programmes. In such cases, the evaluation should include site-specific design criteria and environmental
regulations that affect the cooling water system. Site-specific water supplies should be used whenever
possible. All criteria in this document relating to water compositions, water treatment methods (as
described in Annex A), test unit configuration, heat exchanger design and operating conditions should be
followed insofar as possible.
No laboratory or off-site testing programme can completely duplicate plant conditions. Site-specific factors
(e.g. process leaks, microbiological growth, corrosion products, airborne contamination) can affect the
operation of cooling water systems and the performance of chemical treatment programmes in ways that
override the results of laboratory or off-site testing programmes.
4.1.2 On-site testing
Whenever possible, water treatment programmes should be evaluated on site, using plant water supplies
and actual design and operating conditions, particularly those that cannot be duplicated in the laboratory.
4.1.3 Online testing
Whenever possible, all off-site, laboratory and on-site pilot scale testing should be validated by monitoring
actual performance results online. Pilot units can be adapted for online work by using a side stream from
the plant circulating cooling water as feedwater, bypassing the pilot unit cooling tower. Such online testing
validates offline or laboratory tests. Cooling systems can be evaluated online; however, the data collected
will be the result of the combination of any existing treatment and all additional chemicals that were added
for the evaluation period. Online testing in this way can optimize the treatment programme to meet specific
plant requirements. For example, small quantities of a treatment chemical can be added just ahead of the
test heat exchanger to measure the effects of increasing additive dosage, or the possible synergistic effects
of a new chemical added to the existing treatment programme.
4.2 Cost analysis
Cost analysis of the selected additives should be evaluated according to ISO 22449-2.
5 Test unit design parameters
5.1 General
When designing a pilot-scale evaluation programme for water treatment products, the mechanical design
and operation of each cooling water system shall be evaluated. It can be impractical to simulate a specific

ISO 16784-1:2024(en)
critical plant heat load or water flow pattern exactly. Contamination cannot develop in the same way in
a pilot cooling tower as in the plant systems. Compromises can therefore be necessary. Plant design and
operations shall be followed in all such circumstances. Deviations shall be noted in the test reports.
In addition to adding corrosion and scaling control additives to circulating cooling water, some water
treatment methods are also commonly used for circulating cooling water treatment, including:
— the lime softening method;
— the ion exchange method;
— the reverse osmosis desalting method;
— the electrochemical treatment method;
— the electromagnetic method;
— bypass filtration methods.
These methods are discussed in 5.4. Specific attention shall be given to the impact of using these methods on
additive selection in the design of the pilot unit.
For efficiency, pilot test research can be done on two or more identical test units at the same time.
5.2 Construction materials
5.2.1 Cooling towers
Small cooling tower basins can be made of uncoated, plastic-coated, galvanized low-carbon or stainless
steel. Large tower basins are usually concrete. Splash fill can be wood, ceramic or plastic. It is not important
that the pilot cooling tower duplicates the design of the plant towers. However, if the plant system contains
galvanized steel, galvanized steel should be included as a non-heat-transfer test material in the pilot system.
5.2.2 Film fill
If the plant cooling towers contain film fill, a section of this fill (if available) should be used in the pilot
tower. Film fill consists of closely packed layers of lightweight plastic material, normally PVC, arranged in a
honeycomb-like structure. This maximizes the surface area over which water flows, and thereby improves
evaporation efficiency. However, the increased surface area also encourages deposit formation in the fill.
Deposits can consist of mineral scales formed by the evaporation of water, microbiological deposits and
corrosion products and silt carried into the tower. Biofilms tend to act as a glue that encourages other
deposits to adhere to the fill. Because the space between adjacent layers of fill is often quite small, deposited
material can bridge the fill and block water flow. This is a serious problem, because film fill cannot be
cleaned chemically unless water can flow through all parts of the fill.
Mechanical cleaning, including water lancing, often damages the lightweight fill material. In addition,
the weight of a significant deposit in the film fill can mechanically damage it. Hence, one performance
requirement of any cooling water chemical treatment programme intended for use in a film-fill cooling
tower shall be to prevent bridging of the fill.
The condition of the film fill in an operating cooling tower can be monitored using a fill test box. This is a
section of fill, a cube with sides of 0,6 m, enclosed in a supporting box that is open at the top and bottom.
The box is exposed to droplets of condensation that fall below the fill in the cooling tower, in an accessible
location. If the fill surfaces feel slippery, or if there is a visible deposit layer, this indicates fouling conditions
in the fill.
A fill test box is a very useful qualitative monitoring tool in an operating cooling tower. However, it can be
impractical in a pilot cooling tower due to space and size limitations. It is best to design the pilot cooling
tower so that the actual tower fill can be accessed conveniently for visual and physical inspection.

ISO 16784-1:2024(en)
5.2.3 Non-heat-transfer metal surfaces
Circulating water lines can be lined with carbon steel, copper, brass, fiberglass, polyethylene or cement.
Unless process-side conditions dictate otherwise, heat exchanger shells are usually made of carbon steel.
Bimetallic corrosion shall be avoided.
All corrosion-prone metals that are present in the operating system should be included as non-heat-transfer
test coupons in the pilot study. This is important for two reasons. First, localized corrosion of piping systems
can lead to unexpected failures. Second, corrosion product deposits can accumulate on heat-transfer
surfaces, which can lead to under-deposit corrosion and losses in efficiency. Water treatment chemicals
can only provide corrosion protection when the chemicals can reach the metal surfaces. Unprotected metal
areas beneath deposits thus become potential sites for under-deposit corrosion.
5.2.4 Heat exchangers
Heat exchanger design is generally focused on process-side requirements and on the actual process involved
(liquid cooling, gas cooling or condensing). Process heat exchangers are designed to control the temperature
of a process fluid under the most severe expected conditions. That is, the warmest cooling water and the
maximum production rate.
Heat exchangers are designed with a built-in fouling factor that allows the unit to produce the desired
process temperature control with some loss of efficiency due to either water- or process-side fouling of the
tubes. For these reasons, process heat exchangers are often oversized. To achieve the desired process-side
outlet temperature control, operators throttle the water flow in response to ambient conditions, production
demands and the degree of fouling in the heat exchanger. Reducing the water flow rate through the tubes
increases the surface temperature and allows suspended solids to settle on the tube surfaces and mineral
scale deposits to form. This leads to losses in heat-transfer efficiency and increased opportunities for
corrosion of the tubes. See also 9.3.1.
NOTE The terms "fouling factor" and "fouling thermal resistance" refer to the measured resistance to heat
transfer caused by a deposit on a heat-transfer surface. The fouling factor is also used in heat-exchanger design to
increase the heat-exchanger surface area to compensate for thermal inefficiency caused by a deposit on the heat-
transfer surface. The term "fouling factor" is commonly used for both. However, "fouling thermal efficiency" can be
substituted for the measured fouling factor.
One very important function of the chemical water treatment programme is to minimize corrosion and
deposit formation of all kinds on heat exchanger surfaces. In designing a pilot-scale testing programme, one
critical set of parameters involves the configuration of the heat-transfer section. Heat-transfer tubes can be
made of carbon steel, copper, copper alloys or stainless steels. If required in petrochemical plants or other
locations with severe process-side conditions, heat-transfer tubes can include a wide variety of other alloys
and a few non-metallic materials.
Care should be taken when selecting the heat exchanger to be modelled. The most appropriate heat exchanger
has a combination of the highest surface temperature and the lowest velocity, within reason. Some judgment
is required in the selection process.
Petrochemical plants sometimes include vertically oriented shell-and-tube heat exchangers. Because
of process requirements, water is often on the shell side in such exchangers. Shell-side water creates
particularly severe corrosion and fouling problems that cannot be satisfactorily simulated in the type of
pilot-scale equipment covered by this document. This is especially true of vertical shell-side water heat
exchangers.
Many plant heat exchangers include multi-tube and multi-pass designs. Such designs are difficult to simulate
in a pilot-scale unit. This document refers to single-tube, single-pass designs with parameters selected to
simulate the conditions under study in the plant exchanger.
5.3 Measuring instrument
Online testing instruments shall be used to test the changes of parameters during the experiment, including
but not limited to: temperature, pressure, flow rate, conductivity, pH, online corrosion rate test instrument.

ISO 16784-1:2024(en)
5.4 Other simulation devices
There are a number of water treatment methods for recycling water, which can result in different water
qualities. These methods include:
— the lime softening method,
— the ion exchange method,
— the reverse osmosis desalting method,
— the electrochemical treatment method,
— the electromagnetic method.
The simulators of different water treatment methods should be simulated as part of the pilot-scale equipment
when pilot-scale experiments are carried out.
When the simulation devices are not available in some cases, artificial synthetic water can be used to replace
the effluent of these devices.
6 Operating parameters
6.1 General
For any given heat exchanger design, the kinetics of fouling and corrosion are controlled by three parameters:
surface temperature, water velocity and residence time, in addition to water quality. It is not possible to
duplicate all the characteristics of an operating heat exchanger in a small pilot-scale unit, so compromises
shall be made in controlling each of these parameters.
6.2 Surface temperature
The surface temperature of the heat-transfer surface controls the rate of temperature-driven corrosion and
fouling reactions. The surface temperature, in turn, is a function of the heat flux, metallurgy, water flow and
the degree of water- and process-side fouling of the tubes.
During testing of water treatment programmes under the most severe conditions that can realistically
exist in a specific plant, the surface temperature of the heated tube sections in the pilot unit should match
the highest surface temperature in the operating heat exchanger. This temperature can be estimated from
measured water- and process-side flows and temperatures as well as the design data for the heat exchanger.
6.3 Water velocity
Water velocity through the heat exchanger tubes determines the rate of transfer of dissolved and suspended
matter between the bulk cooling water and the water film in contact with the tube wall. These materials can
include scaling ions (e.g. calcium and carbonate), dissolved ions (the corrosive species in most cooling water
systems), foulants, including suspended solids, and the chemical additives designed to control fouling and
corrosion.
Increasing water velocity normally helps to control both fouling and corrosion. Flow rates between about
1,0 m/s and 2,5 m/s are common. Excessive velocity can cause flow-assisted corrosion, depending on
the tube metallurgy. Lower velocities can be required to closely simulate specific plant heat exchangers
operating with velocities lower than 1 m/s.
6.4 Residence time
In reference to heat exchangers, residence time is the time that water is exposed to the heat-transfer surfaces
in a specific exchanger during each cycle through the cooling system. This cannot be exactly duplicated

ISO 16784-1:2024(en)
in a small pilot unit. However, the effect of residence time per unit of heat-transfer length is simulated by
matching surface temperature and flow velocity to field conditions as closely as possible.
7 Water quality and contamination
7.1 General
This clause discusses the effects of the quality and availability of make-up water for open cooling water
system operation, performance and control, emphasizing problems that shall be considered when designing
specific pilot cooling water test facilities. The quality of the available make-up water can vary seasonally, can
be drawn from several different sources and can be reused after being treated by the different processing
units , as described in 5.1. Such variations should be considered.
7.2 Natural versus synthetic water supplies
For practical reasons, most water treatment product development work is performed in the laboratory,
using waters that have been synthesized to resemble typical natural waters. However, the closer a product
development project comes to actual field use, the more important it is to test on-site, using actual field
water supplies.
Laboratory waters cannot duplicate the organic content of natural waters. Simple organic compounds are
sometimes added in the laboratory to compensate for this, but without much success. Natural lignins and
tannins and process contaminants are site-specific. These materials can have important effects, especially
on the tendency of a water to precipitate mineral scales. Similarly, microbiological contamination from
water and airborne sources cannot be duplicated in the laboratory.
For con
...