Kohlenstoffaustausch zwischen Stahl und Natrium als Korrosionserscheinung

Carbon exchange between steel and sodium as a corrosion phenomenon New analytical methods are applied to measure carbon in liquid sodium in the concentration range below 1 μg C/gNa. The carbon exchange between sodium and austenitic steel under decarburising conditions can be understood on the basis of the results of these analyses. The decarburisation of austenitic steel by sodium may cause a corrosive effect of the surface region of the materials. Some tests with the steel no. 1.4948 have demonstrated a reduction of its creep-rupture strength at 550°C. The corrosion due to decarburisation proceeds slowly, specimens with a larger diameter were not affected, a significant reduction of the creep-rupture strength did not occur.     

Die Verzunderung von Heißgasleitungswerkstoffen für ein luftgekühltes Sonnenturmkraftwerk bei wechselnder Temperaturbelastung zwischen 623 und 1073 K

Scaling of materials for hot gas tubing in an air-cooled solar tower power station under thermal cycling between 623 and 1073 K The corrosion behaviour of two heat resistant alloys X 12 CrNi 2521 (1.4845) and X 10 NiCrAlTi3220 (1.4876) is studied. These alloys are model alloys for hot air pipes of a gas cooled solar tower power station. The maximum operating temperature is 1073 K (solar operation), the minimum is 623 K (fossil operation) during cloudy periods and at night. The experimental simulation device for cyclic temperature exposure between 623 K and 1073 K is described and experimental results are discussed. After 7000 cycles with the tempeature gradient of < 7 K/s growth, composition and adherence of corrosion layers on the materials are determined. The post examinations of the exposed specimens show the better corrosion behaviour of X 12 CrNi2521 not only after isothermal exposure at 1073 K but also after thermal cyclic exposure between 623 and 1073 K.     

Kupfer-, Nickel- und Titanlegierungen für Seewasseranwendungen

Copper and nickel alloys and titanium for seawater applications Copper and nickel alloys and titanium have been successfully used for heat exchangers on ships. In power plants and for chemical apparatus and piping systems because of their resistance against corrosion in sea water. Aluminium brass and copper nickel alloys, the standard materials for condensers and coolers, however, may be attacked, the corrosion depending on water quality, water velocity, and structural conditions. The mechanisms of corrosion are discussed. Under severe conditions the use of titanium may be indecated. The use of nickel base alloys is advantageous at elevated temperatures, e. g. for chemical reactions and for evaporation processes. Examples are given for application and for prevention of corrosion.     

Kondensatorrohre aus Kupferwerkstoffen Richtlinien für Werkstoffauswahl und Betriebsbedingungen

Condenser tubes made of copper materials

• 1 Today, the copper alloys most generally used for condenser tubes are CuZn28Sn (Special brass 71 — Admiralty brass) CuZn20Al (Special brass 76 — Aluminium brass), as well as the copper-nickel alloys CuNi10Fe and CuNi30Fe. The high corrosion resistance of these materials is due to the electropositive normal potential of their base metal — copper — and to their ability to form a highly adhesive, protective sealing film. To counteract the dezinzification of copper-zinc condenser tube materials, alloying with arsenic or phosphorus is indispensable, and generally resorted to.
• 2 The properties of normal-type cooling waters and the phenomena of tube corrosion are discussed. In practice, the only difficulties are likely to arise if polluted waters are used. Especially at the time of commissioning, the tubes must be kept free of polluted water so as to ensure the formation of a dense and firm protective film.
• 3 The reaction of the tube material to the cooling water depends mainly on the p_H-value, on the carbonate, chloride and oxygen contents, and on the temperature and flow rate of the water.
• 4 The following practice rules are advised: For fresh water (containing less than 0.1 pC matter in dissolution) and flow rates exceeding 1.4 metres pr. second, tubes consisting of CuZn20Al or of a copper-nickel alloy should be used so as to avoid erosion-corrosion. If the sea water is greatly polluted, it is advisable — especially at flow rates around or above 3 metres pr. second — to use tubes consisting of CuNi10Fe or CuNi30Fe.

     

Die Korrosionsprobleme der Klein- und Mittelständischen Industrie - eine Herausforderung für die Gesellschaft für Korrosionsschutz

Corrosion problems in small and medium-sized companies - a challenge for Gesellschaft für Korrosionsschutz The Gesellschaft für Korrosionsschutz (GfKORR) attaches high priority to solving problems related to materials and corrosion encountered in small and medium-sized firms. In this connection historical trends are presented and existing activity in the fields of corrosion and corrosion protection in various institutions is analysed. It is demonstrated that, compared with large-scale industries, small and medium-sized industries have the greatest recourse to service organizations. Statistics, derived from the work of the Karl-Winnacker-Institut and the Bundesanstalt für Materialforschung und -prüfung, indicate the types and the distribution of corrosion projects. Implications for the future work of the society are given. In particular this entails the promotion of production and product-integrated corrosion protection which is applicable during the developmental stage of processes and products. It is intended that this approach to problems should replace additive corrosion protection which only takes effect when the damage has occurred.     

Korrosionsverhalten und Biokompatibilität von Titanlegierungen für Implantate

Corrosion behaviour and biocompatibility of titanium alloys for implants Generally titanium alloys have proved to be suitable for implants. But there exist scruples concerning to toxic alloying elements, which were the reason to start comparative examinations with various kinds of titanium alloys. Because of bad reproducibility and high expenditure the obvious way to qualify different alloys by biocompatibility was not practicable. Therefore those properties which can be regarded as prerequisites of good biocompatibility were tested in saline. These are high corrosion resistance and high resistance of the passive layers. Extensive tests demonstrated the suitability of all alloys but no significant differences between titanium and its alloys TiAl6V4, TiAl5Fe2,5, TiAl7Mo4 and TiAl5Nb7. High variances and outlayers indicate that surface treatment is more important than chemical compositions of titanium alloys.     

Zur Herstellung und Anwendung von Ionenaustauschermembranen für die Alkalisalzelektrolyse

Manufacture and application of ion exchange membranes for alkali salt electrolysis Up to 30% by weight of styrene-divi-nylbenzene have been grafted on non-crosslinked high-pressure polyethylene films. Addition of isooctane in different proportions, yields variable degrees of porosity. Sulfonation yields cation exchange membranes, while chlormethylation followed by amination yields anion exchange membranes. In order to characterize the membranes thus obtained, their ion exchange capacities, specific conductivities and permselectivities were determined. The cation exchange membranes were used as diaphragms in the KCl and sodium sulfate electrolysis. Current efficiency and chloride ion diffusion were determined as functions of voltage, current density and degree of porosity and were correlated with the properties cited above.     

Halbleitereigenschaften von Passivfilmen und ihre Bedeutung für die Lochkorrosion

Semiconductive properties of passive films and susceptibility to localized corrosion The semiconductor properties of the passive films on AISI 304 were studied by Mott-Schottky analysis and photoelectrochemical methods. The results were compared with the number of current transients during passivation at different potentials which describe the metastable pitting events. The results show that the onset potential for pit nucleation coincides with the potential at the point of zero charge in the passive film (flat-band potential). A simple electrostatic model is presented showing that the first step of the pit nucleation event - the adsorption of the pit inducing anions - is not possible until a region of positive space charge is present in the passive film. Furthermore the model is confirmed by the appearance of a maximum in the transient number occurring in the same potential range where drastic changes in the electronic properties of the passive film take place.     

Richtlinien für Werkstoffauswahl und Korrosionsschutz in der chemischen Industrie

Criteria for the selection of materials and corrosion protection in the chemical industry In chemical technology, the technical requirements to be met by materials as well as the protection measures against corrosion become more differentiated. On the other hand, owing to the technical progress in the sphere of materials number of alternative solutions to cope with these specifications is becoming available. The selection process, which has thus become more difficult, must lead to an overall solution representing the economic optimum; but must not become too expensive in the planning of new plant or in the corrosion protection of existing plant. A distinction is made between, and a brief outline given of, several stages in the material selection process, viz. formulation of requirements; selection methods prior to testing; laboratory tests; utilisation of technical testing plants; tests under operating conditions; determining the correct solution. The economic calculations designed to determine the most favourable technical solution call for numerous technical data (e.g., the corrosion rates under different corrosion conditions) as well as economic data (especially the capital and annual costs depending on the material). The calculation and estimating methods suitable for this purpose are described in detail. In order to reduce the costs incurred through corrosion, money must be spent on certain protective measures. This relationship is illustrated by the phenomenon of cost substitution. Finally, a synopsis is given of all the practicable methods suitable for determining the optimum conditions.     

Autoklavenanlage für Oxidation und Korrosion von Materialien mit Hochdruckwasser

Autoclave arrangement for oxidation and corrosion tests of materials in pressurized water The authors describe an arrangement with an autoclave for corrosion and oxidation tests in pressurized water and steam. The autoclave has been conceived for a pressure of 250 bar at 500 °C. It is equipped with four locks enabling the specimens to be exchanged during operation without any markable influence on the working conditions. The aggressive medium can be exchanged continuously at a rate of 2,5 l/h. In addition to pressure and temperature controls the arrangement is equipped with a water quality control system.     

Korrosionsschutz – Eine Basis für die Elektronik und Mikrosystemtechnik

Corrosion protection – A basis for electronics and microtechnic systems The number of microtechnic systems grows rapidly and so their influence to the general fail‐safe of technology. Their reliable function in increasing rough environmental conditions is mainly determined by the corrosion protection measures. The corrosion investigation founding shows nevertheless unfortunately deficiencies.     

Die Oxydation von als Umhüllungen für Brennstoffelemente in schnellen Reaktoren verwendeten Metallen durch sauerstoffhaltiges flüssiges Natrium

Oxidation of metals and alloys for cladding of fast reactor fuel elements by oxygen containing liquid sodium Fuel element cladding of stainless steels and vanadium alloys require the use of high purity sodium. Steels have advantages in this respect because they are not sensitive to oxygen in sodium, while V alloys – though having high mechanical strength and good behaviour under irradiation – have but insufficient corrosion resistence. Kinetic laws in the case of V alloys strongly depend upon oxygen concentration; alloying with Ti and Zr, however, can produce a definite improvement in corrosion resistance.     

Korrosions- und Verschleißeigenschaften von Werkstoffen für die chemische Verfahrenstechnik

Corrosion and wear behaviour of materials for chemical engineering It has been estimated that 7.4 percent of all corrosion related failures are mechanically assisted (i.e. involve wear), and that such failure consume, or render useless, 37 million pounds of highly alloyed materials per year. Despite this, relatively little is known of the basic wear behaviour of alloys commonly used in the chemical processing industries, and little attention has been paid to the design of alloys for conditions involving simultaneous corrosion and wear. The objectives of this paper are three-fold. First, the various types of wear are described, and the alloy characteristics required to combat each of these types are discussed. Second, new wear data are presented for several alloys commonly used in the chemical processing industries. Third, a comparison is drawn between these well established materials and a newly introduced cobalt-based alloy designed specifically for corrosion/wear service. The conclusions of the paper are that hardness is a poor indicator of performance for most of wear, that the nickel-chromium-molybdenum alloys are considerably more resistant to cavitation erosion and galling than the austenitic and duplex stainless steels, and that the cobald-based alloy possesses exceptional resistance to slurry erosion, cavitation erosion, and galling.     

Korrosionsreaktionen sauerstoffempfindlicher Metalle in flüssigem Natrium mit Oxidgehalten. I. Reaktionen von Zirkonium und Zircaloy-2

Corrosion reactions of metals sensitive to oxygen in liquid sodium containing oxide. I. Reactions of Zirconium and Zircaloy-2 The corrosion and oxidation behaviour of pure zirconium and of zircaloy-2 has been examined in a sodium circuit with forced sodium circulation. At temperatures ranging from 500 to 600°C, the pure metal as well as the alloy are oxidized, forming external oxide films and internal brittle zones. At a constant oxygen content of about 5 ppm, the reactions are governed by a parabolic law. The constants of the oxidation rate depend on temperature and correspond to an activation energy of 40 kcal/Mol in the case of zirconium. The zirconium alloys have a high resistance in pure sodium and lose virtually no material to the following sodium. In sodium with oxygen content, the corrosion rate up to 550°C is acceptably low. As far as the Getter effect of zirconium is concerned, the formation of external oxide films has an inhibiting effect. However, measurments of the decrease of the oxygen in the sodium showed that, due to the reaction with zirconium at 650°Ca technically useful Getter effect can be obtained.     

Verbesserter Schutz gegen Korrosion und Reibkorrosion für Luftfahrtwerkstoffe durch PVD-Beschichtungen

Improved protection against corrosion and fretting corrosion for aircraft materials by PVD-coatings To substitute the ecologically critical cadmium as corrosion and fretting-corrosion protecting coating for aircraft materials aluminium-based PVD-coatings were tested. Apart from pure Al-coatings, Mg- or Li-alloyed Al-platings, in some cases additionally covered with a tribologically active top-coat (AlN; CrN), were deposited by IBAD- and Arc-techniques on the mild steel 1.7734, the martensitic chromium-steel 1.4548 and the titanium-based alloy 3.7164. In the condensed water- and salt-spray-test the corrosion protection for 1.7734 by Al-, Al/AlMg3- or AlLi-IBAD-coatings was not satisfactory because of the relatively high porosity of these coatings and an inhomogeneous Mg- and Li-distribution in the Al/AlMg3-IBAD- and AlLi-IBAD-platings. By depositing the more homogeneous Arc-coatings AlMg3 and above all AlLi a long-time corrosion protection could be achieved. In comparison to a Cd-plated 1.7734 the fretting-corrosion resistance was slightly improved by an AlLi/AlN-Arc-coating. The corrosion resistance of the electrochemically noble materials 1.4548 and 3.7164 in the condensed water- and the salt-spray-test was not affected by the deposited platings. In comparison to a Cd-coating, the fretting-corrosion resistance was improved by a TiC/i-C-IBAD-plating.     

Untersuchungen und Betrachtungen zur Anwendung von Kunststoffen für Lebensmittel XVI. Mitteilung: Diffusionsvorgänge an PVC-Schläuchen für Lebensmittel

Investigations into and considerations concerning the use of plastics in contact with foodstuffs. XVIth Communication: Diffusion processes in PVC hoses for food products Milk hoses of PVC react with the constituents of milk and – during the subsequent cleaning operations – also with water and cleaning solutions. The diffusion processes taking place in this connection are studied with the aid of specially designed simulating methods (rotating, milk- filled annular hose, testing apparatus reproducing the operation and cleaning of milking machines). After the tests one has determined in particular the transition of plasticiser into the liquid and the transition of fat into the plastic material, while in the case of cleaning solutions the water absorption by the plastic has been determined. The loss of plasticiser and the absorption of fatty materials depend primarily from the swelling condition of the PVC: the higher the swelling of the plastic, the easier the loss of plasticiser. During the contact with milk the then existing fatty film on the plastic inhibits water absorption, but this effect is eliminated by the cleaning operations. With increasing time embrittlement connected with cracking is observed.     

Chlorid-Abspaltung aus o-Dichlorbenzol-Wasser-Gemischen im neutralen und sauren Bereich und ihre Bedeutung für die Werkstoffauswahl

Hydrolysis of o-dichlorobenzene-water-mixtures In neutral to acid conditions and its importance when selecting materials of construction Water-saturated o-dichlorobenzene and o-dichlorobenzene-watermixtures were investigated for hydrolysis under neutral and acid conditions and the exclusion of light. Some measurements were also taken in presence of iron oxides and also metallic iron. Chloride ion generation grows with increasing temperatures and – at 175 °C – also with time. The greatest chloride ion generation was observed when water saturated o-dichlorobenzene reacted in the presence of iron oxides. In the presence of sulfuric acid the maximum chloride ion generation was detected at 175 °C and a sulfuric acid concentration of 3 · 10^?3 mol/l. The hydrolysis products were monochlorobenzene and o-chlorophenol. The chloride ion generation from o-dichlorobenzene in neutral and slightly acid media is important when selecting materials of construction for chemical equipment.     

Expertensysteme für den Korrosionsschutz

Expert systems for corrosion protection technology Corrosion science is a very interdisciplinary special subject, which involves parts of the classic disciplines chemistry, metallurgy and mechanical engineering. Solving of corrosion problems needs the recognition of relations between the different subjects as well as empirical and heuristical knowledge. These are reasons for the loss of 50 billion DM in Germany caused by corrosion damages. By applying existing corrosion control practices 20% per year could be saved. Corrosion experts are very rarely or it is impossible to obtain the required guidence on corrosion. Expert systems are suitable tools for the mentioned problems. In 1985, members of the Laboratory of Corrosion Protection Technologies at the Fachhochschule Hagen started with the development of the expert system CORROS. The domain of CORROS is the corrosion behaviour of corrosion system water/metallic materials.