1、BRITISH STANDARD BS EN 12502-5:2004 Protection of metallic materials against corrosion Guidance on the assessment of corrosion likelihood in water distribution and storage systems Part 5: Influencing factors for cast iron, unalloyed and low alloyed steels The European Standard EN 12502-5:2004 has th
2、e status of a British Standard ICS 23.040.99; 77.060; 91.140.60 BS EN 12502-5:2004 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 45295 6 National foreword This British Standard is the official
3、English language version of EN 12502-5:2004. 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. Cro
4、ss-references 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
5、 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. aid enquirers to understand the text; p
6、resent 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,
7、an inside front cover, the EN title page, pages 2 to 12, 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 EN
8、125025 December2004 ICS77.060;23.040.99;91.140.60 Englishversion ProtectionofmetallicmaterialsagainstcorrosionGuidanceon theassessmentofcorrosionlikelihoodinwaterdistributionand storagesystemsPart5:Influencingfactorsforcastiron, unalloyedandlowalloyedsteels Protectiondesmatriauxmtalliquescontrelacor
9、rosion Recommandationspourlvaluationdurisquedecorrosion danslesinstallationsdedistributionetstockagedeau Partie5:Facteursconsidrerpourlafonte,lesaciers nonallisetfaiblementallis KorrosionsschutzmetallischerWerkstoffeHinweisezur AbschtzungderKorrosionswahrscheinlichkeitin Wasserverteilungsundspeicher
10、systemenTeil5: EinflussfaktorenfrGusseisen,unlegierteund niedriglegierteSthle ThisEuropeanStandardwasapprovedbyCENon22November2004. CENmembersareboundtocomplywiththeCEN/CENELECInternalRegulationswhichstipulatetheconditionsforgivingthisEurope an Standardthestatusofanationalstandardwithoutanyalteratio
11、n.Uptodatelistsandbibliographicalreferencesconcernings uchnational standardsmaybeobtainedonapplicationtotheCentralSecretariatortoanyCENmember. ThisEuropeanStandardexistsinthreeofficialversions(English,French,German).Aversioninanyotherlanguagemadebytra nslation undertheresponsibilityofaCENmemberintoi
12、tsownlanguageandnotifiedtotheCentralSecretariathasthesamestatusast heofficial versions. CENmembersarethenationalstandardsbodiesofAustria,Belgium,Cyprus,CzechRepublic,Denmark,Estonia,Finland,France, Germany,Greece,Hungary,Iceland,Ireland,Italy,Latvia,Lithuania,Luxembourg,Malta,Netherlands,Norway,Pola
13、nd,Portugal, Slovakia, Slovenia,Spain,Sweden,SwitzerlandandUnitedKingdom. EUROPEANCOMMITTEEFORSTANDARDIZATION COMITEUROPENDENORMALISATION EUROPISCHESKOMITEEFRNORMUNG ManagementCentre:ruedeStassart,36B1050Brussels 2004CEN Allrightsofexploitationinanyformandbyanymeansreserved worldwideforCENnationalMe
14、mbers. Ref.No.EN125025:2004:EEN 12502-5:2004 (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.5 4.1 General5 4.2 Uniform corrosion6 4.3 Pitting corrosion 7 4.4 Selective
15、 corrosion8 4.5 Bimetallic corrosion 9 4.6 Erosion corrosion10 5 Assessment of corrosion likelihood11 Bibliography 12 EN 12502-5:2004 (E) 3 Foreword This document (EN 12502-5:2004) has been prepared by Technical Committee CEN/TC 262 “Metallic and other inorganic coatings”, the secretariat of which i
16、s 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 2005, and conflicting national standards shall be withdrawn at the latest by June 2005. This standard is in five parts: Part 1:
17、General Part 2: Influencing factors for copper and copper alloys Part 3: Influencing factors for hot dip galvanised ferrous materials 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 pa
18、ckage of interrelated European Standards with a common 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, Denm
19、ark, 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. EN 12502-5:2004 (E) 4 Introduction This document mainly results from inves
20、tigations into and experiences gained of the corrosion of unalloyed and low alloyed ferrous materials (steels and cast irons) in contact with supply waters and raw waters in once- through flow systems. The corrosion likelihood of unalloyed and low alloy ferrous materials (steels and cast irons) in c
21、ontact with water depends on the layers built up from corrosion products that might or might not be protective. When layers are present that are not protective, tuberculation can appear on the walls of the components and can lead to corrosion effects such as: sludge in water, colouring (red or black
22、 water), reduction of free section of pipes or even wall perforation. As a result of the complex interactions between the various influencing factors, 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 us
23、e of unalloyed and low alloy ferrous materials in water systems. It can be used to minimize the likelihood of corrosion damages occurring by: assisting in designing, installing and operating systems from an anti-corrosion point of view; evaluating the need for additional corrosion protection methods
24、 for a new or existing system; assisting in failure analysis, when failures occur in order to prevent repeat failures occurring. However, a corrosion expert, or at least a person with technical training and experience in the corrosion field is required to give an accurate assessment of corrosion lik
25、elihood or failure analysis. EN 12502-5:2004 (E) 5 1 Scope This document reviews the influencing factors for the corrosion likelihood of bare unalloyed or low alloyed ferrous materials (mild steels and cast irons) used as tubes, tanks and equipment in water distribution and storage systems, except f
26、or water intended for human consumption. NOTE See EN 12502-1. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document
27、(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
28、:1999). 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. 3.2 Symbols c(O 2 ) concentration of oxygen in mmol/l c(HCO 3 - ) concentration of hydrogen carbonate ions in mmol/l
29、c(Ca 2+ ) concentration of calcium ions in mmol/l4 Types of corrosion 4.1 General The most common types of corrosion are described in EN 12502-1:2004, Clause 4. The types of corrosion considered for steels and cast irons are the following: uniform corrosion; pitting corrosion; selective corrosion; b
30、imetallic corrosion; erosion corrosion. EN 12502-5:2004 (E) 6 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; characteristics of the water; design and construction; pressure t
31、esting and commissioning; operating conditions. 4.2 Uniform corrosion 4.2.1 General Uniform corrosion of steel and cast iron is associated with the transfer of iron (II) ions into the water (metal loss). These ions dissolved in the water can react with oxygen to form less soluble iron (II)-(III)-hyd
32、roxy compounds leading to turbidity and sludge formation. These corrosion effects usually do not lead to corrosion damages. Under flowing conditions with waters containing sufficient amounts of calcium carbonate, protective layers consisting of calcium carbonate and hydrated iron oxides can be forme
33、d if the intensity of localized corrosion is low enough. With similar waters under stagnant conditions, localized corrosion always occurs. 4.2.2 Influence of the characteristics of the metallic material The chemical composition and microstructure of these materials as well as the cold deformation ha
34、ve virtually no influence on uniform corrosion. 4.2.3 Influence of the characteristics of the water In oxygen containing waters, corrosion damage because of uniform corrosion only occurs when protective layers cannot form. The precondition for the formation of a protective layer is a water compositi
35、on with: c(O 2 ) 3 mg/land pH 7,0 and c(HCO 3 - ) 2 mmol/l and c(Ca 2+ ) 1 mmol/lThe type and concentration of natural components (e.g. phosphates, aluminosilicates) dissolved in the water can play an important part in the formation of protective layers. In the absence of protective layers, the corr
36、osion rate is determined by the concentration of oxidizing agents and/or acidic agents, e.g. carbon dioxide. The uniform corrosion rate is very low if: c(O 2 ) 8,5 EN 12502-5:2004 (E) 7 4.2.4 Influence of design and construction In water lines designed for water under mainly stagnant conditions, e.g
37、. sprinkler systems, the oxygen concentration rapidly drops under 1 mg/l as a consequence of corrosion. At the same time the pH value increases above 8. The rate of uniform corrosion is insignificant under these conditions. However, if fresh oxygenated water is brought into the system during testing
38、, then blockage of sprinkler heads with corrosion debris can result. 4.2.5 Influence of pressure testing and commissioning Pressure testing and commissioning have no influence on uniform corrosion. 4.2.6 Influence of operating conditions Significant variations of operating conditions can modify unif
39、orm corrosion. If no protective scale is formed the rate of uniform corrosion increases with increasing flow rate and/or temperature. For the effect of stagnant conditions, see 4.2.4. 4.3 Pitting corrosion 4.3.1 General Pitting corrosion is the most frequent corrosion effect on steels and cast irons
40、 in water distribution and storage systems. It develops from galvanic cells depending on surface conditions of materials, water parameters and service conditions. Anodic areas always form in metallic regions, when the entry of oxygen is hindered by geometrical factors, e.g. in crevices. The bare met
41、allic areas with non-restricted oxygen access form the cathodic area. The corrosion manifests itself in either shallow or steep-sided pits. Pitting corrosion can be enhanced by microbial activity, which can take place in anaerobic conditions, especially under debris. Generally, corrosion rates are h
42、igh and can rapidly lead to wall perforation of the system. The outer manifestation of corrosion is the formation of tubercles under which anodic areas are to be found, cathodic areas being characterized by relatively thin surface layers. 4.3.2 Influence of the characteristics of the metallic materi
43、al Pitting corrosion is influenced by the fact that steels and cast irons are iron-carbon alloys with additional elements, intentionally present or as impurities. For materials with compositions given in EN 545, the influence of alloying elements is usually less important than that of other heteroge
44、neities. The surface quality influences the formation of galvanic cells. Anodic areas are favoured by deposits of all types, e.g. oxide scales, residues of oil and paint, corrosion products. EN 12502-5:2004 (E) 8 4.3.3 Influence of the characteristics of the water The likelihood of pitting corrosion
45、 decreases with increasing concentration of hydrogen carbonate ions because they are part of a buffering system that is able to neutralize the acidity caused by hydrolysis of the iron ions within the pit. The likelihood of pitting corrosion increases with increasing concentrations of chloride, sulfa
46、te and nitrate ions because they replace hydrogen carbonate ions and are not able to buffer the acidity formed within in the pit. Surface waters that contain higher amounts of organic matter increase the likelihood of microbially enhanced pitting corrosion. 4.3.4 Influence of design and construction
47、 Stagnant conditions, which favour the onset of pitting corrosion, predominantly occur in dead legs in iron and steel pipes. Crevices formed by hidden recesses, lap joints, badly executed joints and other geometrical factors can induce anodic spots of corrosion elements. The introduction of organic
48、materials, e.g. oil, grease, which can be a source of nutrient for micro-organisms, favour the occurrence of microbial corrosion. In sprinkler systems a very high risk of pitting corrosion exists in the tubes coming from storage vessels with pressurized air, because of the high oxygen content of this water. 4.3.5 Influence of pressure testing and commissioning If pressure testing is not done according to the recommendations given in EN 12502-1:2004, 5.5, leaving residual water in t
