1、BRITISH STANDARD BS EN 12502-3:2004 Protection of metallic materials against corrosion Guidance on the assessment of corrosion likelihood in water distribution and storage systems Part 3: Influencing factors for hot dip galvanised ferrous materials The European Standard EN 12502-3:2004 has the statu
2、s of a British Standard ICS 23.040.99; 77.060; 91.140.60 BS EN 12502-3:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 20 January 2005 BSI 20 January 2005 ISBN 0 580 45296 4 National foreword This British Standard is the official English
3、 language version of EN 12502-3:2004. The UK participation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-refe
4、rences The 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 the BSI Electronic Catalogue or of Britis
5、h 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. aid enquirers to understand the text; present
6、to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an insi
7、de front cover, the EN title page, pages 2 to 14, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsEUROPEANSTANDARD NORMEEUROPENNE EUROPISCHENORM EN125023
8、December2004 ICS77.060;23.040.99;91.140.60 Englishversion ProtectionofmetallicmaterialsagainstcorrosionGuidanceon theassessmentofcorrosionlikelihoodinwaterdistributionand storagesystemsPart3:Influencingfactorsforhotdip galvanisedferrousmaterials Protectiondesmatriauxmtalliquescontrelacorrosion Recom
9、mandationspourlvaluationdurisquedecorrosion danslesinstallationsdedistributionetstockagedeau Partie3:Facteursconsidrerpourlesmtauxferreux galvanisschaud KorrosionsschutzmetallischerWerkstoffeHinweisezur AbschtzungderKorrosionswahrscheinlichkeitin WasserverteilungsundspeichersystemenTeil3: Einflussfa
10、ktorenfrschmelztauchverzinkteEisenwerkstoffe ThisEuropeanStandardwasapprovedbyCENon22November2004. CENmembersareboundtocomplywiththeCEN/CENELECInternalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanationalstandardwithoutanyalteration.Uptodatelistsandbibliographical
11、referencesconcernings uchnational standardsmaybeobtainedonapplicationtotheCentralSecretariatortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undertheresponsibilityofaCENmemberintoitsownlanguageandnotifiedtotheCent
12、ralSecretariathasthesamestatusast heofficial versions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Cyprus,CzechRepublic,Denmark,Estonia,Finland,France, Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Poland,Portugal, Slovakia, Slovenia,S
13、pain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels 2004CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMembers. Ref.No.EN125023:2004:EEN 1
14、2502-3:2004 (E) 2 Contents Page Foreword3 Introduction .4 1 Scope 5 2 Normative references 5 3 Terms, definitions, and symbols5 3.1 Terms and definitions .5 3.2 Symbols 5 4 Types of corrosion.6 4.1 General6 4.2 Uniform corrosion7 4.3 Pitting corrosion 8 4.4 Selective corrosion11 4.5 Bimetallic corro
15、sion 12 5 Assessment of corrosion likelihood13 Bibliography 14 EN 12502-3:2004 (E) 3 Foreword This document (EN 12502-3:2004) 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 th
16、e status of a national standard, either by publication of an identical text or by endorsement, at the latest by June 2005, and conflicting national standards shall be withdrawn at the latest by June 2005. This standard is in five parts: Part 1: General; Part 2: Influencing factors for copper and cop
17、per alloys; Part 3: Influencing factors for hot dip galvanized ferrous material; Part 4: Influencing factors for stainless steels; Part 5: Influencing factors for cast iron, unalloyed and low alloyed steels. Together these five parts constitute a package of interrelated European Standards with a com
18、mon date of withdrawal (dow) of 2005-06. 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, Hun
19、gary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. EN 12502-3:2004 (E) 4 Introduction This document results mainly from investigations into and experience gained of the corrosi
20、on of hot dip galvanized ferrous materials, used as steel tubes and cast iron fittings (galvanized products), in drinking water distribution systems in buildings. However, it can be applied analogously to other water systems. The corrosion likelihood of galvanized products depends on the formation o
21、f a corrosion product layer, which begins to form as soon as the galvanized surface comes in contact with water. The more this layer prevents ionic and electronic exchanges between the metal and water, the more protective it will be and the higher the durability of the galvanized products. Drinking
22、water systems with galvanized products, although showing visible corrosion effects, are, in general, resistant to corrosion damage in normal use. However, there are conditions under which they will sustain corrosion damage. As a result of the complex interactions between the various influencing fact
23、ors, the extent of corrosion can only be expressed in terms of likelihood. This document is a guidance document and does not set explicit rules for the use of hot dip galvanized ferrous materials in water systems. It can be used to minimize the likelihood of corrosion damages occurring by: assisting
24、 in designing, installing and operating systems from an anti-corrosion point of view; evaluating the need for additional corrosion protection methods for a new or existing system; assisting in failure analysis, when failures occur in order to prevent repeat failures occurring. However, a corrosion e
25、xpert, or at least a person with technical training and experience in the corrosion field is required to give an accurate assessment of corrosion likelihood or failure analysis. EN 12502-3:2004 (E) 5 1 Scope This document gives a review of influencing factors of the corrosion likelihood of hot dip g
26、alvanized steel and cast iron, used as tubes, tanks and equipment, unalloyed and low alloy ferrous materials in water distribution and storage systems as defined in EN 12502-1. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated
27、 references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN ISO 8044:1999, Corrosion of metals and alloys Basic terms and definitions (ISO 8044:1999). EN 12502-1:2004, Protection of metallic materials again
28、st corrosion Guidance on the assessment of corrosion likelihood in water distribution and storage systems Part 1: General. 3 Terms, definitions, and symbols 3.1 Terms and definitions For the purposes of this document, the terms and definitions given in EN ISO 8044:1999 and EN 12502- 1:2004 apply. 3.
29、2 Symbols c(HCO 3 - ) Concentration of hydrogen carbonate ions in mmol/lc(Cl - ) Concentration of chloride ions in mmol/l c(SO 4 2- ) Concentration of sulphate ions in mmol/lc(NO 3 - ) Concentration of nitrate ions in mmol/lc(Ca 2+ ) Concentration of calcium ions in mmol/lEN 12502-3:2004 (E) 6 4 Typ
30、es of corrosion 4.1 General Internal corrosion of galvanized products in water distribution and storage systems generally leads to the build-up of layers formed by corrosion products, which might or might not be protective. Because a metal coating produced by hot dip galvanizing is not a homogeneous
31、 layer consisting of zinc alone, but a structured system of zinc and various zinc-iron alloy phases, after some time the corrosion products will also contain iron compounds. Because of the greater solubility of the zinc compounds, the layers end up consisting of iron corrosion products (rust). In th
32、e case of non-protective layers, corrosion can lead to the impairment of the function of the system (lack of serviceability because of corrosion damage). The most common types of corrosion are described in EN 12502-1:2004, Clause 4. The types of corrosion considered for galvanized products are the f
33、ollowing: uniform corrosion; pitting corrosion; selective corrosion; bimetallic corrosion. The various possibilities are shown schematically in Tables 1 and 2. Table 1 Uniform corrosion and its consequences Low rate uniform corrosion High rate uniform corrosion Corrosion effects on zinc coating Form
34、ation of a protective layer on residual zinc coating, which remains during full service life. Complete loss of zinc coating. Corrosion effects on the base metal None Uniform attack, low mass loss; protective rust layer Non-uniform attack, pits, tubercles Possible corrosion damage (during projected s
35、ervice life) None Initially high concentration of metal ions in water Reduction in free pipe bore size Table 2 Localized corrosion and its consequences Pitting corrosion Selective corrosion Corrosion effects on the coating Localized loss of coating Intergranular attack leading to complete loss of th
36、e zinc phase Corrosion effects on the base metal Pits and tubercles Non-uniform general corrosion Possible corrosion damage (during projected service life) Reduction of free pipe bore size, contamination of water by iron corrosion products, blockage of system components, wall perforation Initial rel
37、ease of solid zinc corrosion products into water, contamination of water by iron corrosion products EN 12502-3:2004 (E) 7 For each type of corrosion, the following influencing factors (described in EN 12502-1:2004, Table 1 and Clause 5) are considered: characteristics of the metallic material; chara
38、cteristics of the water; design and construction; commissioning and pressure testing; operating conditions. To assess the influence of the characteristics of the water, data as described in EN 12502-1 are necessary. Therefore, the composition of the water fed into the respective installations is rel
39、evant. However, temporary variations of the water composition need to be considered. Therefore, in addition to a detailed analysis of the water, information about its variations is necessary. 4.2 Uniform corrosion 4.2.1 General Experience shows that corrosion damage to galvanized products because of
40、 uniform corrosion can only occur if the corrosion velocity is extremely high and there is no possibility of stable protecting rust layers being formed. Uniform corrosion can manifest itself in different ways (see Table 1). Uniform corrosion leads to the formation of layers consisting of zinc hydrox
41、ycarbonates, which, depending on the carbonic acid species concentration, can offer the product greater or lesser degrees of protection. If the corrosion rate is sufficiently low, no complete loss of the zinc layer will occur during the projected service life. Protective layers will form on the rema
42、ining zinc phase of the metal coating. At a higher corrosion rate, the metal coating will be completely removed during the projected service life. The concentration of iron corrosion products in the surface layer increases during the corrosion of the zinc-iron alloy phases. Further corrosion process
43、es eventually result in the formation of a surface layer consisting predominantly of aged iron corrosion products, which provide lasting corrosion protection. If the corrosion rate of the coating is too high, or the concentration of the components forming the carbonic acid system too low to allow th
44、e formation of a protective layer, the base metal will be non-uniformly attacked after the consumption of the metal coating. The consequence can be contamination of the water by iron corrosion products, encrustation and clogging of the pipes or wall penetration by pitting corrosion. Although zinc co
45、rrosion products are only sparingly soluble, zinc ions are released into water. The concentration of zinc ions because of dissolution of corrosion products will depend on: the concentration of the carbonic acid species in the water; the duration of stagnation of water in pipes; the age of the instal
46、lation; the dilution caused by mixing with fresh water; the method of sampling. The quantity of loosely adherent zinc corrosion products that can be removed from the tube walls will depend on: the duration of low water velocity; the extent of sudden turbulent flow. EN 12502-3:2004 (E) 8 4.2.2 Influe
47、nce of the characteristics of the metallic material Physical and chemical characteristics and surface conditions of the metallic material on the degree of uniform corrosion are not known to influence uniform corrosion. 4.2.3 Influence of the characteristics of the water Under flowing conditions, the
48、 rate of uniform corrosion of zinc strongly depends on the pH value of the water. It increases with decreasing pH value of the incoming water. Under stagnant conditions, the quantity of zinc ions going into solution is predominantly determined by the carbonic acid species concentration, in particular the carbon dioxide concentration. The rate of uniform corrosion can be decreased by the addition of inhibitors, e.g. orthophosphates, or by alkalization of the water by additi
