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
This document gives a review of influencing factors of the corrosion likelihood of hot dip galvanized 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.
Korrosionsschutz metallischer Werkstoffe - Hinweise zur Abschätzung der Korrosionswahrscheinlichkeit in Wasserverteilungs- und speichersystemen - Teil 3: Einflussfaktoren für schmelztauchverzinkte Eisenwerkstoffe
Dieses Dokument enthält eine Übersicht der Einflussfaktoren für die Korrosionswahrscheinlichkeit von Rohren, Behältern und Zubehörteilen, die aus schmelztauchverzinktem Stahl und schmelztauchverzinktem Temperguss hergestellt sind, in Wasserverteilungs- und -speicherungssystemen, wie sie in EN 12502-1 definiert werden.
Protection 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 à considérer pour les métaux ferreux galvanisés à chaud
Le présent document étudie les facteurs influant sur le risque de corrosion des matériaux en acier et en fonte galvanisés à chaud utilisés dans les tubes, les réservoirs et les équipements ainsi que les matériaux faiblement alliés et non alliés dans les installations de distribution et de stockage d'eau, définies dans le prEN 12502-1.
Protikorozijska zaščita kovinskih materialov - Navodilo za ocenjevanje verjetnosti nastanka korozije v porazdeljeni vodi in skladiščnih sistemih - 3. del: Vplivni dejavniki za vroče pocinkane železove materiale
Standards Content (Sample)
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
SIST EN 12502-3:2005
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
EN 12502-3:2004 (E) 2 Contents Page Foreword.3 Introduction.4 1 Scope.5 2 Normative references.5 3 Terms, definitions, and symbols.5 3.1 Terms and definitions.5 3.2 Symbols.5 4 Types of corrosion.6 4.1 General.6 4.2 Uniform corrosion.7 4.3 Pitting corrosion.8 4.4 Selective corrosion.11 4.5 Bimetallic corrosion.12 5 Assessment of corrosion likelihood.13 Bibliography.14
SIST EN 12502-3:2005
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 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: General; Part 2: Influencing factors for copper and copper 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 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, 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.
SIST EN 12502-3:2005
EN 12502-3:2004 (E) 4 Introduction This document results mainly from investigations into and experience gained of the corrosion 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 of 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 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 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.
SIST EN 12502-3:2005
EN 12502-3:2004 (E) 5 1 Scope This document gives a review of influencing factors of the corrosion likelihood of hot dip galvanized 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 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 against 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. 3.2 Symbols c(HCO3-) Concentration of hydrogen carbonate ions in mmol/l c(Cl-) Concentration of chloride ions in mmol/l c(SO42-) Concentration of sulphate ions in mmol/l c(NO3-) Concentration of nitrate ions in mmol/l c(Ca2+) Concentration of calcium ions in mmol/l SIST EN 12502-3:2005
EN 12502-3:2004 (E) 6 4 Types 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 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 the 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 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
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; characteristics 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 relevant. 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 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 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. SIST EN 12502-3:2005
EN 12502-3:2004 (E) 8 4.2.2 Influence 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 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 addition of NaOH and/or Na2CO3, by addition of Ca(OH)2 or by use of filters, e.g. marble, limestone, dolomite. The rate of uniform corrosion in a water distribution system decreases in the flow direction. This is because water flowing through hot dip galvanized pipes will be depleted of oxygen and carbon dioxide by the corrosion process and becomes less corrosive than fresh water. 4.2.4 Influence of design and construction The formation of protective layers will be favoured by regular renewal of the water, which can be facilitated by avoiding areas of stagnation. 4.2.5 Influence of pressure testing and commissioning If pressure testing is not done according to the recommendations given in EN 12504-1, 5.5, and residual water is left in the system after draining, the likelihood for the formation of loosely adherent corrosion products is increased. 4.2.6 Influence of operating conditions 18.104.22.168 Influence of temperature The effect of temperature on uniform corrosion of zinc is complex because of changes in the composition of the corrosion products in the surface layer. Up to temperatures of approximately 35 °C, the rate of uniform corrosion increases with temperature. Above this temperature, the corrosion rate tends to decrease because the predominant corrosion product in flowing cold water, zinc hydroxide, is converted to less soluble zinc oxide. 22.214.171.124 Influence of flow conditions The rate of uniform corrosion under stagnant conditions in a particular water is always lower than under flowing conditions. It increases with water flow velocity. 4.3 Pitting corrosion 4.3.1 General 126.96.36.199 Manifestations of pitting corrosion Depending on the water temperature, there are two different types of pitting corrosion that can occur on galvanized products. SIST EN 12502-3:2005
EN 12502-3:2004 (E) 9 188.8.131.52 Pitting corrosion in cold water In cold water systems, pitting corrosion manifests itself mainly in the formation of pits. It results in the development of pustules, which reduce the free pipe bore size over the course