1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58on the assessment of corrosion likelihood in closed water circulation systemsThe European Standard
2、EN 14868:2005 has the status of a British StandardICS 77.060Protection of metallic materials against corrosion Guidance BRITISH STANDARDBS EN 14868:2005BS EN 14868:2005This British Standard was published under the authority of the Standards Policy and Strategy Committee on 27 September 2005 BSI 27 S
3、eptember 2005ISBN 0 580 46664 7Cross-referencesThe British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of t
4、he BSI Electronic Catalogue or of British Standards Online.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard does not of itself confer immunity from legal obligations.Summary o
5、f pagesThis document comprises a front cover, an inside front cover, the EN title page, pages 2 to 23 and a back cover.The BSI copyright notice displayed in this document indicates when the document was last issued.Amendments issued since publicationAmd. No. Date CommentsA list of organizations repr
6、esented on this committee can be obtained on request to its secretary.enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK.National forewordThis British Standard is the official
7、 English language version of EN 14868:2005.The UK participation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any EU
8、ROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN 14868August 2005ICS 77.060English VersionProtection of metallic materials against corrosion - Guidance onthe assessment of corrosion likelihood in closed watercirculation systemsProtection des matriaux mtalliques contre la corrosion -Recommandations po
9、ur lvaluation du risque de corrosiondans les systmes ferms recirculation deauKorrosionsschutz metallischer Werkstoffe - Leitfaden frdie Ermittlung der Korrosionswahrscheinlichkeit ingeschlossenen Wasser-ZirkulationssystemenThis European Standard was approved by CEN on 8 July 2005.CEN members are bou
10、nd to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Cen
11、tral 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 translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as t
12、he officialversions.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, S
13、weden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUROPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2005 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.R
14、ef. No. EN 14868:2005: EEN 14868:2005 (E) 2 Contents page Foreword 3 Introduction4 1 Scope .5 2 Normative references .5 3 Terms and definitions.5 4 Symbols and abbreviations6 5 Types of corrosion6 6 Role of oxygen 7 7 Microbial corrosion.8 8 Corrosion damage in Case I conditions8 9 Corrosion damages
15、 in Case II systems.11 10 Corrosion protection methods.15 Annex A (informative) Important corrosion reactions in the systems under consideration.19 Bibliography.22 EN 14868:2005 (E) 3 Foreword This European Standard (EN 14868:2005) has been prepared by Technical Committee CEN/TC 262 “Metallic and ot
16、her 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
17、 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
18、, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EN 14868:2005 (E) 4 Introduction This European Standard results mainly from investigations into and experience gained on the corrosion of metallic
19、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 no
20、rmal 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
21、 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
22、 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 t
23、o minimize the likelihood of corrosion damage occurring. EN 14868:2005 (E) 5 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 wat
24、er 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
25、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
26、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, lo
27、cal 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 late
28、st 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 alloy
29、s - 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 stee
30、l) 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 EN 14868:2005 (E) 6 4 Symbols an
31、d abbreviations c(Cl-) Concentration of chloride ions in mmol l-1c(HCO3-) Concentration of hydrogen carbonate ions in mmol l-1c(SO42-) Concentration of sulphate ions in mmol l-1c(NO3-) Concentration of nitrate ions in mmol l-15 Types of corrosion When evaluating the corrosion likelihood in water cir
32、culation 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 corrosio
33、n; 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
34、 and other detrimental effects. EN 14868:2005 (E) 7 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.
35、 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
36、 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 dif
37、fusion 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 p
38、ressure 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
39、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
40、 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
41、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
42、 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 a
43、re introduced into the circulating water. EN 14868:2005 (E) 8 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 to
44、o 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 cooli
45、ng 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
46、oxygen ingress. However, if the circulation water is regularly renewed because of losses in the system and excessive amounts of fresh water are added (more than 2 times initial fill volume) oxygen ingress will almost certainly lead to significant impairment of the system. 7 Microbial corrosion Micro
47、-organisms (algae, yeasts, fungi, bacteria etc.) can exist in debris left in the system after construction or can enter the system with the initial filling water or via open header tank during operation. In Case II systems, this can lead to bio-fouling problems and can also give rise to microbial co
48、rrosion irrespective of metallic materials used in the system. Although corrosion is favoured at moderate temperatures, not even the high temperatures in heat exchangers are always sufficient to kill all micro-organisms and some bacteria are thermophiles. Favourable conditions (nutrients, inorganic
49、ions and organic contaminants, possibly also from some water treatment additives) favour growth of microbiological organisms. Bacterial growth is also favoured by stagnant conditions, especially under deposits, in dead legs or crevices formed during manufacturing operations. Their metabolism produces organic acids, which promote initiation and acceleration of localised corrosion cells. The most well known case is anaerobic bacteria, especially sulphate reduci
