Stainless Steel in Contact with Other Metallic Materials

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CONTACT WITH OTHER METALLIC MATERIALS, Euro Inox is the European market development asso Full members. ciation for stainless steel Members of Euro Inox include. European stainless steel producers Acerinox,www acerinox es. national stainless steel development associations, development associations of the alloying element Outokumpu. www outokumpu com,industries, The prime objectives of Euro Inox are to create aware ThyssenKrupp Acciai Speciali Terni. www acciaiterni com, ness of the unique properties of stainless steel and to fur.
ther its use in existing applications and in new markets ThyssenKrupp Nirosta. www nirosta de, To achieve these objectives Euro Inox organizes confer. ences and seminars and issues guidance in printed and ArcelorMittal Stainless Belgium. ArcelorMittal Stainless France, electronic form to enable architects designers speci. www arcelormittal com, fiers fabricators and end users to become more familiar. with the material Euro Inox also supports technical and. market research Associate members,www acroni si,British Stainless Steel Association BSSA. www bssa org uk,www cedinox es,Centro Inox,www centroinox it.
Informationsstelle Edelstahl Rostfrei,www edelstahl rostfrei de. Institut de D veloppement de l Inox I D Inox,www idinox com. International Chromium Development Association ICDA. www icdachromium com,International Molybdenum Association IMOA. www imoa info,Nickel Institute,www nickelinstitute org. Paslanmaz elik Derne i PASDER,www turkpasder com,Polska Unia Dystrybutor w Stali PUDS.
www puds pl,SWISS INOX,www swissinox ch,CONTACT WITH OTHER METALLIC MATERIALS. Table of contents, Stainless Steel in Contact with Other Metallic Materials 1 Introduction 2. Materials and Applications Series Volume 10 2 The principles of galvanic corrosion 3. ISBN 978 2 87997 263 3 3 Relevant factors and examples 5. Euro Inox 2009 3 1 Electrolyte resistance 5,3 2 Wetting duration and environments 6. Translated and adapted from ARLT N BURKERT A 3 3 The kinetics of electrode reactions 8. ISECKE B Edelstahl Rostfrei in Kontakt mit anderen 3 4 Cathode and anode area 8. Werkstoffen Merkblatt 829 D sseldorf Informations 4 Practical experience in different applications 10. stelle Edelstahl Rostfrei 4th edition 2005 4 1 Water and sewage treatment 11. 4 2 Components in atmospheric conditions 14, Publisher 4 3 Stainless steel in building and construction 15. Euro Inox 4 4 Stainless steel in transport applications 18. Diamant Building Bd A Reyers 80 Frequently asked questions 20. 1030 Br ssel Belgium 5 Preventing galvanic corrosion 22. Phone 32 2 706 82 65 Fax 32 2 706 82 69 6 Literature 23. Disclaimer, Euro Inox has made every effort to ensure that the infor.
mation presented in this document is technically correct. However the reader is advised that the material con. tained herein is for general information purposes only. Euro Inox its members specifically disclaim any liabili. ty or responsibility for loss damage or injury resulting. from the use of the information contained in this publi. Photo credits Copyright notice, Atomium asbl vzw Brussels B This work is subject to copyright Euro Inox reserves all. Centro Inox Milan I rights of translation in any language reprinting re use of. Bundesanstalt f r Materialpr fung und forschung illustrations recitation and broadcasting No part of this. Berlin D publication may be reproduced stored in a retrieval. David Cochrane Sidcup UK system or transmitted in any form or by any means. Beno t Van Hecke Hasselt B electronic mechanical photocopying recording or. Outokumpu Tornio FIN otherwise without the prior written permission of the. Thomas Pauly Brussels B copyright owner Euro Inox Luxembourg Violations may. Christoph Seeberger Munich D be subject to legal proceedings involving monetary. ThyssenKrupp Nirosta GmbH Krefeld D damages as well as compensation for costs and legal. Sch ck Bauteile GmbH Baden Baden D fees under Luxemburg copyright law and regulations. Viega GmbH Co KG Attendorn D within the European Union. CONTACT WITH OTHER METALLIC MATERIALS,1 Introduction. Complex design requirements can make sion potential of the metals in contact hence. it necessary to combine different metallic there is usually a corrosion hazard for the. materials within the same component Also partner material. chance combinations can often be found The risk of galvanic corrosion occurring. governed only by the availability of for in depends however on a multitude of factors. stance fasteners or shims In certain cir Besides the materials used environment. cumstances such mixed material designs and design are crucial It is therefore diffi. can lead to corrosion in one of the partner cult to make a priori judgments about. materials This phenomenon includes gal the compatibility of materials The present. vanic corrosion1 in which two different publication describes the principles of galva. metals form a galvanic couple nic corrosion and the main parameters. As a result of the formation of galvanic that allow designers to estimate corrosion. elements accelerated corrosion of the less risk,noble material can occur The latter may then. suffer a corrosion rate far higher than that to,be expected without any contact with the. nobler partner metal Corrosion related dam,age such as unacceptable deterioration of.
appearance leaking tubes or failing fasten,ers can drastically reduce the service life of. a component and lead to premature re, placement In most technical applications Accelerated corrosion of a metal due to the effect of a corrosion ele. ment Other factors include concentration elements aeration elements. stainless steel has the more positive corro and active passive elements. CONTACT WITH OTHER METALLIC MATERIALS,2 The principles of galvanic corrosion. For galvanic corrosion to occur there naturally occur in the metal in isolation how. must be ever the corrosive attack on the anode is, different corrosion potentials of greatly accelerated In some cases the for. the metals within a given system mation of galvanic elements can lead to cor. a conductive connection between the rosion in materials that would otherwise be. two metals corrosion resistant in the environment in. an electrically conductive humidity question This can be the case for passive. film electrolyte connecting both materials such as aluminium which can be. metals locally polarised in a certain environment In. Figure 1 shows the three prerequisites in such cases localised corrosion phenomena. graphic form such as crevice corrosion or pitting corrosion. If galvanic corrosion occurs the less no can be observed which would not have. ble material the anode is preferentially occurred without the shift in potential. attacked whilst the more noble material caused by the formation of galvanic ele. the cathode is even protected against ments,corrosion In fact the principle of cathodic.
protection is based on sacrificial anodes,providing protection from corrosion. The contact of two metals with different,potentials in an electrically conductive solu. tion leads to a flow of electrons from the,anode to the cathode The electro chemical. reactions are the same as those that would,Electrolyte. Metal 1 Metal 2,Anode Cathode Figure 1,shows the three prerequi.
sites in graphic form,CONTACT WITH OTHER METALLIC MATERIALS. Contrary to widespread belief the differ,ence of potential in an electrochemical cell. Alloy 625 C 276 alone is not a good indicator of the actual. Superaustenitic stainless steel,risk of galvanic corrosion It only indicates. Alloy 400 whether or not such a risk has to be taken. Austenitic stainless steel grade 1 4404 316 L passive. into account In this context it should be, Ni Al Bronze remembered that the numerous published. 90 10 Cupro Nickel, Al brass tables of the standard potentials of metals.
only provide an approximation of differences,Austenitic stainless steel casting. Lead of potential The decisive factor is not the,Carbon steel. difference of potential observed under stan, Cast steel dardised experimental conditions but rather. Zinc the actual difference of potential under real. Magnesium operating conditions This is why empirical. tables of galvanic series have been produced,2000 1500 1000 500 0 500. Potential mV SCE,for typical environments such as sea water.
These position the potential of various met,als in a given environment Figure 2. Figure 2 Awareness of the prerequisites of gal, The Galvanic Series in vanic corrosion and a proper understanding. sea water at 10 C 11,of the examples in Figure 3 make it possible. to determine preventive action which will be,discussed in section 5. Conditions in which,galvanic corrosion,cannot occur.
Galvanic corrosion cannot occur, without electrically in metals with no without connection by an electrolyte. conductive joints difference of potential,Electrolyte Electrolyte Electrolyte Electrolyte. Metal 1 Metal 2 Metal 1 Metal 2 Metal 1 Metal 2 Metal 1 Metal 2. Metal 1 Anode Metal 2 Cathode,CONTACT WITH OTHER METALLIC MATERIALS. 3 Relevant factors and examples, According to Faraday s law electro chem reduced and the shift of potential at the an. ical corrosion processes are directly related ode is limited as illustrated in Figure 4. to charge transfer i e the flow of currents Measurement of potential at the surface. Currents or current densities are therefore identifies in the case of an insulated anode. frequently used to measure corrosion If the the position of the respective potentials of. conditions for galvanic corrosion are met in cathode and anode independently of each. principle the total corrosion current Itot is other In the transition area a marked jump. composed of a partial current from self in potential is observed If an electrically. corrosion Is i e the part of the corrosion that conductive connection between cathode. is independent of contact with other materi and anode exists a low polarisation of the. als and a partial cell current Iel i e the part anode towards higher values is observed. of the corrosion due to the cell current be,tween the partner materials Equation 1.
Itot Is Iel Equation 1,Intensity of element corrosion is deter. mined by the difference of potential between Low resistance High galvanic corrosion. the two metals DU the electrolyte resis High resistance Low galvanic corrosion. tance Rel and the polarisation resistance at Insulated anode No galvanic corrosion. the anode Rp a and cathode Rp c respec,tively Equation 2. Cathode Anode,Anode Cathode,Iel DU Equation 2,Rel Rp a Rp c. From this equation inferences can be,drawn concerning the factors that determine. galvanic corrosion These factors are critical Figure 4. in determining whether or not metallic cor in electrolytes with high resistance such as Influence of electrolyte. rosion will become a technically relevant water films resulting from condensation In resistance on anode. polarisation, problem The effects of these factors will the case of electrolyte films of low resistance.
therefore be discussed individually salt water a very strong polarisation is. measured The higher the polarisation the,higher the corrosion rate of the anode if the. 3 1 Electrolyte resistance material is active or the higher the probabil. ity of reaching critical corrosion initiating, The risk of galvanic corrosion diminishes potential if the material is in its passive state. with increasing electrolyte resistance This is Table 1 shows specific conductivity values of. because the reach of the galvanic current is various types of water. CONTACT WITH OTHER METALLIC MATERIALS,3 2 Wetting duration. and environments,There is a strong interaction between. electrolyte resistance and duration of wet,ting This is of critical importance wherever.
components are not permanently wetted by,watery liquids As explained in the descrip. tion of the prerequisites of galvanic corro,sion the electrolyte film plays a key role. Without such a film no galvanic corrosion,can occur This implies that in practice any. combination of metallic materials is uncriti,cal from a corrosion point of view if no elec. trolyte film is present This is typical of inte,riors without condensation In lighting.
fixtures or interior decoration components,virtually any material combination can be. used in normally aerated and heated envi,ronments without restrictions in terms of. corrosion risk Figure 5,Both length of exposure and electrolyte. resistance are strongly dependent on local,conditions In marine industrial or indoor. swimming pool environments the probabil,ity of galvanic corrosion is significantly high.
er than in rural atmospheric conditions,Figure 6 shows the influence of the environ. Typical values of specific ment on the corrosion rate of zinc with and. conductivity in different,types of water,Environment Specific conductivity in V cm 1. Pure water 5 10 8,Demineralised water 2 10 6,Rain water 5 10 5. Drinking water 2 10 4 1 10 3,Brackish river water 5 10 3. Sea water 3 5 10 2 5 10 2,CONTACT WITH OTHER METALLIC MATERIALS.
without contact with stainless steel It,demonstrates that the proportion of cell. Stainless Steel in Contact with Other Metallic Materials Diamant Building Bd A Reyers 80 1030 Brussels Belgium Tel 32270682 67 Fax 69 e mail info euro inox org www euro inox org Materials and Applications Series Volume 10 ISBN 978 2 87997 263 3 Metal 1 Anode Metal 2 Cathode E lectro yte e C ONTACT WITH OTHER METALLIC MATERIALS Euro Inox Euro Inox is the European market development

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