EN 14868:2005

SLOVENSKI STANDARD
01-november-2005
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Protection of metallic materials against corrosion - Guidance on the assessment of
corrosion likelihood in closed water circulation systems
Korrosionsschutz metallischer Werkstoffe - Leitfaden für die Ermittlung der
Korrosionswahrscheinlichkeit in geschlossenen Wasser-Zirkulationssystemen
Protection des matériaux métalliques contre la corrosion - Recommandations pour
l'évaluation du risque de corrosion dans les systemes fermés a recirculation d'eau
Ta slovenski standard je istoveten z: EN 14868:2005
ICS:
77.060 Korozija kovin Corrosion of metals
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 14868
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2005
ICS 77.060
English Version
Protection of metallic materials against corrosion - Guidance on
the assessment of corrosion likelihood in closed water
circulation systems
Protection des matériaux métalliques contre la corrosion - Korrosionsschutz metallischer Werkstoffe - Leitfaden für
Recommandations pour l'évaluation du risque de corrosion die Ermittlung der Korrosionswahrscheinlichkeit in
dans les systèmes fermés à recirculation d'eau geschlossenen Wasser-Zirkulationssystemen
This European Standard was approved by CEN on 8 July 2005.
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 Central Secretariat 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 Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 14868:2005: E
worldwide for CEN national Members.

Contents page
Foreword .3
Introduction.4
1 Scope .5
2 Normative references .5
3 Terms and definitions.5
4 Symbols and abbreviations.6
5 Types of corrosion.6
6 Role of oxygen .7
7 Microbial corrosion.8
8 Corrosion damage in Case I conditions.8
9 Corrosion damages in Case II systems.11
10 Corrosion protection methods.15
Annex A (informative) Important corrosion reactions in the systems under consideration.19

Bibliography.22

Foreword
This European Standard (EN 14868:2005) has been prepared by Technical Committee CEN/TC 262 “Metallic
and other inorganic coatings”, 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 February 2006, and conflicting national standards shall be withdrawn
at the latest by February 2006.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland
and United Kingdom.
Introduction
This European Standard results mainly from investigations into and experience gained on the corrosion of
metallic materials normally present in water circulation systems in buildings (unalloyed and low alloyed steels,
cast iron, aluminium, copper and copper alloys, stainless steels).
Because of the complex interactions between the various influencing factors, which can alter during service
life due either to normal operation changes in service conditions or accidental events, the extent of corrosion
can only be expressed in terms of likelihood. This European Standard therefore is a guidance document and
does not set explicit rules for the use of metallic materials in water systems.
A correct evaluation of the corrosion likelihood therefore needs a corrosion expert (or at least a person with
technical training in the corrosion field) and knowledge of the technology and operating conditions of the
system considered.
Though incidences of severe damage because of corrosion (and/or scaling) are generally rare, certain basic
precautions should be taken in order to maintain a long-term, trouble-free service. This European Standard
should therefore be considered as a guidance document. On the basis of the information provided herein,
decisions can be made during design, installation and service life to minimize the likelihood of corrosion
damage occurring.
1 Scope
This European Standard gives a review of influencing factors on the corrosion likelihood of metallic
components (pipes, tanks, vessels, heat exchangers, pumps etc.) in water circulation systems in buildings.
The water circulation systems considered are:
 heating systems (up to 110 °C service water temperature);
 cooling and chilling systems;
which are filled with potable water or water of similar composition according to the Directive 98/83/EC.
NOTE 1 Sanitary hot water systems with a re-circulation loop are not considered in this European Standard as they are
not really closed system, because the water is continually renewed. The corrosion likelihood of these systems is discussed
in EN 12502 Parts 1 to 5 [1], [2], [3], [4], [5].
NOTE 2 Cooling systems with open atmospheric towers are not considered in this European Standard because fresh
water is generally added to the system periodically to compensate for losses by evaporation or blow-down.
NOTE 3 Heating systems in buildings, connected to district heating systems without an intervening heat exchanger, are
not considered in this European Standard. However, local heating systems, where several buildings are heated by one
boiler plant, are included.
2 Normative references
The following referenced documents are indispensable for the application of this European Standard. For
dated references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 12502-1:2004 Protection of metallic materials against corrosion - Guidance on the assessment of
corrosion likelihood in water distribution and storage systems - Part 1: General
EN ISO 8044:1999 Corrosion of metals and alloys - Basic terms and definitions (ISO 8044:1999)
3 Terms and definitions
For the purposes of this European Standard, the terms and definitions given in EN ISO 8044:1999, EN
12502-1:2004 and the following apply.
3.1
ferrous materials
cast iron, unalloyed and low alloyed steel (excluding stainless steel)
3.2
sludge formation
build-up of non-adherent particulate corrosion products which can be suspended and/or deposited in the
system
3.3
scaling
formation of relatively thick layers of calcium carbonate and/or corrosion products, especially on heat transfer
surfaces
4 Symbols and abbreviations
- -1
c(Cl ) Concentration of chloride ions in mmol l
- -1
c(HCO ) Concentration of hydrogen carbonate ions in mmol l
2- -1
c(SO ) Concentration of sulphate ions in mmol l
- -1
c(NO ) Concentration of nitrate ions in mmol l
5 Types of corrosion
When evaluating the corrosion likelihood in water circulation systems almost all types of corrosion should be
taken into consideration.
The following types of corrosion can occur in the systems under consideration:
 uniform corrosion;
 localised corrosion:
 pitting corrosion;
 bimetallic corrosion;
 crevice corrosion;
deposit corrosion;

 water-line corrosion;
 selective corrosion (de-alloying);
 erosion corrosion;
 cavitation corrosion;
 stress corrosion cracking;
 microbial corrosion.
These types of corrosion can lead to different kinds of corrosion damage:
 leakage;
 constriction of flow;
 reduction of efficiency;
 boiler noise;
 seizure of movable components and other detrimental effects.
6 Role of oxygen
6.1 General
In the systems under consideration, the corrosion processes are mainly determined by the extent of oxygen
ingress into the system. Generally, oxygen reduction is the driving force for anodic metal dissolution reactions.
If the ingress of oxygen can be prevented, the rate of corrosion will be minimised to the extent that corrosion
damages will normally not occur.
Oxygen can enter the system in different ways:
 as dissolved oxygen in the filling and any make-up water;
 from the atmosphere into the water within an open expansion vessel or some so-called de-aeration units
and with some kinds of pressurisation systems (e.g. compressor or pump pressurisation systems);
 from the atmosphere in the case of negative pressure (e.g. through gaskets, O-rings on valves or some
automatic air vents);
 from the atmosphere by diffusion through organic materials (e.g. plastic pipes without barrier, rubber
hoses or rubber membranes of air-filled expansion vessels and some so-called de-aeration systems);
 as dissolved oxygen in drinking water in the case of defective secondary heat exchangers for domestic
hot water, where the pressure in the domestic hot water is greater than in the primary heating water;
 from air pockets remaining in the system after refilling during maintenance or modification.
Corrosion becomes negligible after consumption of the oxygen initially present in the filling water provided that
the water is not renewed and no air entry is possible. The main concern with a closed system is therefore to
maintain water and air tightness. However, in some systems, especially large complex ones, maintaining
complete air tightness can be impractical.
6.2 Influence of design and operating conditions on oxygen ingress
With respect to oxygen ingress, two cases should be considered:
 Case I: systems with no significant oxygen ingress;
 Case II: systems with continuous or intermittent oxygen ingress.
Case I is defined by the fact that practically no oxygen ingress is possible during service. Oxygen dissolved in
the initial fill water is quickly used up in forming corrosion products, which in most cases does not lead to
impairment of the system.
Case II is characterised by the fact that oxygen ingress is possible during service either occasionally, regularly
or continuously.
Systems designed to represent Case I can become Case II during service depending on operating conditions.
Examples of Case I are as follows:
a. Systems with a closed expansion vessel, which are correctly designed, installed and maintained.
b. Open vented heating systems under conditions where only negligible amounts of oxygen are introduced
into the circulating water.
Examples of Case II are as follows:
c. Open vented systems where during service the re-circulating water is regularly enriched with oxygen.
d. Systems with closed expansion vessels in situations where:
 volume of the expansion vessel is too small;
 gas pressure within the dry expansion vessel is not correctly adjusted to match the water pressure;
 gas pressure decreases during service;
 water volume decreases because of water loss (e.g. from valves and pumps).
Such circumstances can result in negative pressure in the system during cooling phases (e.g. overnight),
leading to oxygen ingress through O-rings or gaskets and automatic air vents.
e. Systems with continuous oxygen ingress by diffusion through the walls of organic materials, e.g. plastic
pipes, rubber hoses.
NOTE Refilling of a system does not normally lead to significant oxygen ingress. However, if the circulation wat
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