SIST EN 12502-4:2005

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 4: Einflussfaktoren für nichtrostende StähleProtection 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 4 : Facteurs a considérer pour les aciers inoxydablesProtection of metallic materials against corrosion - Guidance on the assessment of corrosion likelihood in water distribution and storage systems - Part 4: Influencing factors for stainless steels91.140.60Sistemi 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 12502-4:2004SIST EN 12502-4:2005en01-marec-2005SIST EN 12502-4:2005SLOVENSKI
STANDARD



SIST EN 12502-4:2005



EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12502-4December 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 4: Influencing factors for stainless steelsProtection des matériaux métalliques contre la corrosion -Recommandations pour l'évaluation du risque de corrosiondans les installations de distribution et de stockage d'eau -Partie 4 : Facteurs à considérer pour les aciers inoxydablesKorrosionsschutz metallischer Werkstoffe - Hinweise zurAbschätzung der Korrosionswahrscheinlichkeit inWasserverteilungs- und
speichersystemen - Teil 4:Einflussfaktoren für nichtrostende StähleThis 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 12502-4:2004: ESIST EN 12502-4:2005



EN 12502-4:2004 (E) 2 Contents Page Foreword.3 Introduction.4 1 Scope.5 2 Normative references.5 3 Terms and definitions.5 4 Materials.5 5 Types of corrosion.5 5.1 General.5 5.2 Pitting corrosion.6 5.3 Crevice corrosion.8 5.4 Stress corrosion.9 5.5 Knife-line corrosion.10 5.6 Corrosion fatigue.11 6 Assessment of corrosion likelihood.11 Bibliography.12
SIST EN 12502-4:2005



EN 12502-4:2004 (E) 3 Foreword This document (EN 12502-4:2004) 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 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 package of inter-related 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 12502-4:2005



EN 12502-4:2004 (E) 4 Introduction This document mainly results from investigations into and experience gained of the corrosion of stainless steel materials used as tubes, fittings or vessels in drinking water distribution systems in buildings. However, it can be applied analogously to other supply water systems. The corrosion resistance of products made of stainless steel immersed in waters exists because of the presence of a very thin passive layer. Stainless steels in water systems are, in general, resistant to corrosion, although there are certain conditions under which they can 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 stainless steels 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. NOTE Stainless steels are used for domestic pipework, in the food industry and, more importantly, in the chemical industry covering a variety of aggressive environments and service conditions. This explains the existence of a significant number of steel grades each with specific corrosion resistance and also specific mechanical properties.
SIST EN 12502-4:2005



EN 12502-4:2004 (E) 5 1 Scope This document gives a review of influencing factors of the corrosion likelihood of stainless steels used as tubes, tanks and equipment 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 and definitions
For the purposes of this document, the terms and definitions given in EN ISO 8044:1999 and EN 12502-1:2004 apply. 4 Materials For the purpose of this document, the term “stainless steel” includes all martensitic, ferritic, austenitic-ferritic and austenitic steels conforming to the requirements of EN 10088-1 [2], EN 10088-2 [3] and EN 10088-3 [4]. Examples of steel grades that are used or that can be considered as candidate materials for supply water installations are listed in EN 10312 [5]. This document also applies to stainless casting alloys, which are commonly used for the production of valves and fittings and which are of the same composition type as the steels listed in EN 10088, Parts 1 to 3. The casting alloys can be considered as equivalent to their wrought counter parts, provided that no sensitization of the material remains after manufacturing (to be checked by testing the resistance against intergranular corrosion). 5 Types of corrosion
5.1 General The most common types of corrosion are described in EN 12502-1:2004, Clause 4. The rate of uniform corrosion of stainless steels in water distribution and storage systems is negligible because of their passive state. Under the conditions prevailing in water systems stainless steels are usually the more noble materials and hence are not endangered by bimetallic corrosion. The likelihood of intergranular corrosion is negligible in the systems under consideration.
Discoloration of the material’s surface resulting from deposition of foreign corrosion products is not indicative of corrosion of the stainless steel. SIST EN 12502-4:2005



EN 12502-4:2004 (E) 6 In some cases, however, the passive layer of these materials can be locally destroyed. This can result in localized corrosion attack, which can lead to failure because of corrosion damage. The types of corrosion considered for stainless steels comprise the following:  pitting corrosion;  crevice corrosion;  stress corrosion;  knife-line corrosion;  corrosion fatigue. 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 testing and commissioning;  operating conditions. 5.2 Pitting corrosion 5.2.1 General Pitting corrosion occurs only when the potential is more noble than a critical value, which is referred to as pitting initiation potential. The pitting initiation potential depends on parameters related to both the material and the water composition. Pitting corrosion can occur only if the redox-potential of the water is more positive than the pitting initiation potential. 5.2.2 Influence of the characteristics of the metallic material The likelihood of pitting corrosion in stainless steels decreases with increasing chromium, molybdenum and nitrogen contents. It is increased for sulfur-enriched stainless steels (e.g. free-cutting stainless steels used for valves and fittings). Clean metal surfaces exhibit the smallest likelihood of pitting corrosion. Mechanical damage to the surface of finished products, e.g. by scratching or coarse grinding, results in an increased susceptibility of stainless steels to pitting corrosion and stress corrosion cracking. Metallic particles of unalloyed and low-alloy steels can become embedded in the stainless steel surface during machining or handling. They can act as small anodes of corrosion cells, the cathode of which is the stainless steel. In the course of the dissolution of the anodes, the local concentration of chloride ions will be increased by ion migration, and therefore the likelihood of pitting corrosion increases. Furthermore, the corrosion likelihood can also be increased by the iron (III)-bearing corrosion products formed during the dissolution of the anodes, because these corrosion products are more effective oxidizing agents than the dissolved oxygen and favour the conditions necessary for the occurrence of pitting corrosion.
Sensitization can also lead to an increase in the likelihood of pitting corrosion. Incorrect heat treatment or welding procedures, where the material remains for a prolonged period of time in the temperature range of SIST EN 12502-4:2005



EN 12502-4:2004 (E) 7 500 °C to 800 °C leads to precipitation of chromium-rich carbides at the grain boundaries and consequent depletion of chromium in the vicinity of the boundaries. This change in the material is referred to as sensitization.
Sensitization can be revealed by testing in accordance with EN ISO 3651-2 [6]. Materials in the as-fabricated condition should be resistant to this test. Sensitization during fabrication and welding, especially with wall thicknesses greater than 6 mm, can be avoided by following the recommendations from the material’s manufacturer. 5.2.3 Influence of the characteristics of the water The likelihood of pitting corrosion of stainless steels increases as the chloride ion concentration in the water increases, if the
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