EN 12502-3:2004

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Korrosionsschutz metallischer Werkstoffe - Hinweise zur Abschätzung der Korrosionswahrscheinlichkeit in Wasserverteilungs- und
speichersystemen - Teil 3: Einflussfaktoren für schmelztauchverzinkte EisenwerkstoffeProtection des matériaux métalliques contre la corrosion - Recommandations pour l'évaluation du risque de corrosion dans les installations de distribution et de stockage d'eau - Partie 3 : Facteurs a considérer pour les métaux ferreux galvanisés a chaudProtection 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 materials91.140.60Sistemi za oskrbo z vodoWater supply systems77.060Korozija kovinCorrosion of metals23.040.99Drugi sestavni deli za cevovodeOther pipeline componentsICS:Ta slovenski standard je istoveten z:EN 12502-3:2004SIST EN 12502-3:2005en01-marec-2005SIST EN 12502-3:2005SLOVENSKI
STANDARD
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12502-3December 2004ICS 77.060; 23.040.99; 91.140.60English versionProtection of metallic materials against corrosion - Guidance onthe assessment of corrosion likelihood in water distribution andstorage systems - Part 3: Influencing factors for hot dipgalvanised ferrous materialsProtection des matériaux métalliques contre la corrosion -Recommandations pour l'évaluation du risque de corrosiondans les installations de distribution et stockage d'eau -Partie 3 : Facteurs à considérer pour les métaux ferreuxgalvanisés à chaudKorrosionsschutz metallischer Werkstoffe - Hinweise zurAbschätzung der Korrosionswahrscheinlichkeit inWasserverteilungs- und
speichersystemen - Teil 3:Einflussfaktoren für schmelztauchverzinkte EisenwerkstoffeThis European Standard was approved by CEN on 22 November 2004.CEN members are bound 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 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 translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the 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, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2004 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12502-3:2004: ESIST EN 12502-3:2005

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 use of hot dip galvanized 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 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 likelihood or failure analysis.
The types of corrosion considered for galvanized products are the following:  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 Formation 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 service 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 the 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 release of solid zinc corrosion products into water, contamination of water by iron corrosion products SIST EN 12502-3:2005

4.2.1 General Experience shows that corrosion damage to galvanized products because of 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 hydroxycarbonates, 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 remaining 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 processes 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 the 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 corrosion 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 installation;  the dilution caused by mi
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