Die atmosphärische Korrosion von Kupfer und Bronze im Rahmen des UN/ECE-Expositionsprogramms. Zwischenbericht nach 4-jähriger Bewitterung

The atmospheric corrosion of copper and bronze within the UN/ECE Exposure Programme. Intermediate report after 4 years of exposure Accompanied by an extensive measuring programme for environmental data, copper (DIN 1787) and bronze samples (DIN 1705) were exposed at 39 test sites in 14 countries and examined afterwards. Measured were the weight change, the mass loss (after pickling of the corrosion products), the colour changes (trichromatic colorimetry), the chemical composition of the corrosion products (Debye-Scherrer), the layer thickness (eddy-current method), and the roughness of the weathered surface (perthometer). The corrosion data are related with the environmental data, especially the concentration of sulfur dioxide, the relative humidity and the conductivity of precipitations.     

Über den beschleunigenden Einfluß von Schwefeldioxid und Wasser auf die atmosphärische Korrosion von verrosteten Eisen

The accelerating effect of sulphur dioxide and water on the atmospheric corrosion of rusty iron The atmospheric corrosion process of rusty steel was observed in the laboratory in an atmosphere with 1, 10 and 100 p.p.m. SO₂, respectively, at a temperature of 30°C. It was found that the correlation of the corrosion rate with humidity can, in the range between critical humidity and nearly 100 per cent. Relative humidity, be represented by a rising quadratic parabolic equation. The differences in the three SO₂ concentrations had no influence on the corrosion kinetics, which is explained by the fact that, under the testing conditions, the rust was fully saturated with SO₄^2?. On the strength of these and earlier results, the authors submit a new working theory concerning the atmospheric corrosion of already rusty steel, introducing the theories of Heusler and Florianovitsch-Kolotyrkin into the sphere of atmospheric corrosion.     

Off- und Online-Scanning verfahrenstechnischer Kolonnen Prüfung auf Integrität und Funktion

Radiometric off- and on-line scanning of columns in chemical plants Investigation of structural integrity and functionality Radiometric density measurements by scanning of columns and similar devices have been performed successfully for several years for evaluating the structural integrity as well as the performance of these devices. The test equipment developed by the authors provides computer controlled simultaneous movement of a gamma-ray source and a radiation detector parallel to the axial direction of the column. The radiation absorption will be recorded in each position along this way. Lateral position, e.g. for sector scanning, and local resolution can be chosen with respect to the problem addressed. Some typical examples demonstrate the potential of the system to detect mechanical failure on internal structures as well as disfunction. Therefore this inspection technology is able to provide valuable indications for the process engineers for the analysis of process disturbances.     

Der Einfluß des Prüpotentials und der Wärmebehandlung auf das Korrosionsverhalten niob- und titanstabilisierter ferritischer Chromstähle mit rund 17% Chrom

The influence of test potential and heat treatment on the corrosion behaviour of ferritic chromium steels stabilized with niobium or titanium By means of corrosion-chemical, electrochemical, metallographical and electronmicroscopical investigations, the influence of the electrode potential and the heat treatment on the corrosion behaviour of steels of the X 8 CrTi 17 and X 8 CrNb 17 has been determined. With ferritic 17 pC chromium steels, a distinction must be made between two different types of grain boundary corrosion:

• (1) Grain boundary corrosion on steels which were quenched at high temperatures and therefore sensitized, unstabilized or understabilized, due to the segregation of chrome-rich carbides at the grain boundaries, causing a chromium reduction in their vicinity (typical inter-crystalline corrosion), and
• (2) Grain boundary corrosion on steels quenched at high temperatures but fully stabilized, due to the chemical dissolution of the type MX carbonitrides segregated at the grain boundaries during quenching (carbide corrosion).

The heat treatment conditions conducive to carbide corrosion were determined, and the correlation of this type of corrosion with the potential was ascertained by potentio-static tests in sulphuric acid and compared with the behaviour of synthetic carbides. The different corrosion behaviour of the ferritic chromium steels quenched at high temperature and stabilized with niobium and titanium, respectively, is attributed to the different chemical dissolution rates of the carbo-nitrides segregated. The findings also provide an explanation of the corrosion behaviour of sensitization-annealed, stabilized austenitic chrome-nickel steels in acid solution.     

Feste Korrosionsprodukte – I. Magnesium,Zink, Cadmium,Blei und Kupfer

Solid corrosion products – I. Magnesium, zinc, cadmium, lead and copper The instrumental methods for the analysis and the characterisation of solid corrosion products are reviewed and the fundamentals for the construction of stability diagrams are outlined. In the special part, the corrosion products of Mg, Zn, Cd, Pb and Cu are treated. It contains informations about lattice type, solubility, natural occurrence and the morphology of the corrosion products. Only such compounds are considered which are formed in the atmosphere, in natural waters or in the soil.     

Eine universelle Einrichtung für die Prüfung der atmosphärischen Korrosion von Metallen und Schutzüberzügen

Universal accelerated weathering cabinet for weathering tests of metals and protective coatings The authors have developed a accelerated weathering cabinet with visual observation of specimens during the test. The temperature can be controlled between 0 and 50°C by a current of warm air and a thermostat, while a humidification device enables the relative humidity to be controlled between 50 and 95%. Aggressive additions such as sulphur dioxide, aerosols, salt spray etc. are added through a spray system. Sulphur dioxide concentrations can be controlled between 0.1 and 10 ppm and 1 to 100 ppm respectively.     

Elektronenoptische und röntgenographische Untersuchung einer Eisenphosphat-Schutzschicht auf Eisen

Electron-optical and radiographical examination of a protective iron phosphate layer on iron The protective effect of a novel anticorrosive containing phosphoric acid has been examined for its dependence on mineralogical conditions. The base material contains, intro alia, phosphoric acid, potash mica, organic wetting agents and dyeing agents. Vivianite formation has been precluded by radiographic comparison with natural vivianite and with data quited in technical literature. The scraped protective layer was found to contain, apart from muscovite and α iron, dendritic formations which were observed under the electron microscope and identified, from their diffraction interferences, as cubic form of the potassium iron (III) phosphate leucophosphite \documentclass{article}\pagestyle{empty}\begin{document}$ KFe_2 [OH(PO_4)_2] \cdot 2\ H_2 O. $\end{document} KFe₂[OH(PO₄)₂] · 2 H₂O. Precision zone diffraction diagrams of individual dendrites showed a_o = 7.75 ± 0.05 Å and the transmission directions [100]^X [010]^X [202]^X, identical to those observed with natural pharmacosiderite, an iron arsenate corresponding to leucophosphite. Natural and synthetic leucophosphite are monoclinic; if Fe³⁺ is replaced by Al³⁺, and (PO₄)^3? by (AsO₄)^3?, a cubic alumopharmacosiderite is formed. The formation is thereofore interpreted as a cubic modification of leucophosphite, corresponding to pharmacosideriote. A structure comparison shows the epitactic growth of the leucophosphite with [110] and [333] on α iron [100] and [111]. The presence of leucophosphite directly on the iron surface is proved by electron diffraction with grazing incidence of the electron ray.     

Qualitätsmanagement und Akkreditierung von Prüflaboratorien

Quality management and accreditation of laboratories The paper deals with quality management in testing laboratories emphasizing on the one hand the technical aspects as calibration, internal and external quality control and validation, and on the other hand management aspects, i.e. quality documentation, management review and quality audits. The necessity of accreditation of testing laboratories in the legal area of testing and the advantages in the private area are stressed. After an illustration of the difference between accreditation of testing laboratories and certification of quality systems some trends in accreditation and quality management are mentioned.     

Allgemeine Prüfungsmethoden im Zusammenhang mit Alterung und Korrosion von Kunststoffen

General test methods concerning the ageing and corrosion of plastics Following a brief synopsis of the causes of, and phenomena associated with, the ageing or corrosion of plastics, the author discusses the possibilities, mainly on the basis of generally recognised (e.g. standardised) methods, of a controlled simulation and acceleration of the phenomena encountered during storage and consumption. In this connection, the following effects are discussed: heat, oxygen (ozone), moisture, chemicals, organisms, light and weather, as well as mechanical fatigue stresses. Examples are given for combined or successive stresses which are more in keeping with actual practice than the effects of individual components. Finally, some advice is given concerning the choice of suitable test methods by which the changes can be as-certained. The planning of such investigations must always be governed by the objective. This can be fairly reliably achieved if a proper correlation between test method and practical experience is ensured; but it can only be partly achieved in connection with the assessment of new materials whose future performance is to be predicted.     

Einfluß der chemischen Zusammensetzung auf die Kinetik der atmosphärischen Korrosion von Stählen

The influence of the chemical composition on the kinetics of the atmospheric corrosion of steel A total of 19 different structural steels were exposed to urban, rural and industrial atmospheres for periods up to three years. The evaluation of the weight losses determind at certain intervals permitted the establishment of a linear relationship which can be used for assessing, within certain limits of concentration, the influence of specific alloying elements. The tests showed that the effects of the different alloys varies with the type of atmosphere and with the degree of corrosion, and may well shift from “favourable” to “detrimental”. The results are also influenced by the quantitative ratios of certain components. The corrosion behavior of the steels is consistently governed by P, S and Cu and, to a lesser extent, by C and Mn.     

Charakterisierung der Prepassiv- und Passivschicht auf Eisen durch XPS,AES und Reflexionsspektroskopie

Characterization of the Prepassive and Passive Layer on Iron by XPS, AES and Reflectance Spectroscopy The prepassive and passive layers of iron, preferably produced in borate and carbonate/bicarbonate buffers of pH 8.4, cathodically and anodically of the Flade potential, were investigated by XPS, AES and reflexion spectroscopy. The XPS measurements revealed: The prepassive layer is thinner than the passive one. Both layers can be differentiated by the relative height of the XPS signals of oxygen at 530 and 531 eV which points to a higher fraction of OH groups in the surface layer of the passive region. Sputtering decreased the differences in the XP spectrum, i.e. the hydroxidic layer is localized at the electrolyte side. In the case of borate buffer the passive layer contains boron. In carbonate/bicarbonate buffer no iron carbonate layer is formed but also an oxidic/hydroxidic layer. Prepassive and passive layers show characteristic differences in reflection spectrum and aging behaviour.     

Einfluß von bituminösen Dachbelagsmaterialien auf das Korrosionsverhalten von Dachentwässerungssystemen aus Zink und verzinktem Stahl

Influence of bitumineous roof coverings on corrosion behaviour of roof draining systems made of zinc and galvanized steel In long time weathering and laboratory tests on a number of different bitumineous roof coating materials it was confirmed that they are the cause of damage on zinc roof draining systems. The acidic corrosion capacity rain_water is very increased by the formation of acids in bitumineous materials. The formation of acids is almost independent of the different types of bitumineous base materials, but can be reduced by adequate gravel or state covering. But only alkaline mineral coverings, found in a few cases, give sufficient protection against corrosion of zinc. Further important influence which cause corrosion damages is the relation of bitumineous roof area to zinc area and the particular conditions of water draining.     

Einfluß des entstehenden Rostes auf den Verlauf der atmosphärischen Korrosion von Stahl

Influence of incipient rust on the pattern of the atmospheric corrosion of steel The corrosion pattern with continuous rust formation has been compared with the results obtained and accumulated at certain intervals during the same time from analogous specimens. It was found, firstly, that there is a critical value of SO₂ concentration and, secondly, that the existing rust is capable of keeping certain quantities of SO₂ away from the surface. The latter effect explains the flattening-out of the corrosion rate to constant values, as well as the fact that, in pure atmosphere, the stationary conditions are reached later than in an industrial atmosphere.     

Einflüsse von Silicium und Kohlenstoff auf die Sulfidierung von Eisen

Effects of silicon and of carbon on the sulfidation of iron The corrosive attack of steels by H₂S under FeS formation is impeding the use of heat exchangers in processes in which sulfidizing gases occur at low oxygen pressures – the project was aimed at finding ways and means to retard or suppress the FeS growth. Thermogravimetric investigations in H₂? H₂S at 400 °C showed that during the first 100 h of sulfidation a transition takes place from the linear kinetics controlled by the phase boundary reaction H₂S ? S (in FeS) + H₂ to the parabolic kinetics controlled by solid state diffusion in the corrosion products. During this transition the linear constant decreases with time and increasing sulfur activity a_s at the FeS surface (k₁ ? 1/a_s). Upon sulfidation of Fe-6%Si an internal Fe₃Si layer is formed te sulfidation is retarded since for long time ( 100 h) the slow surface reaction at high a_s is rate determining. Carbon deposits formed in carburizing atmospheres (a_c 1) on the iron surface, have a negligible effect on the sulfidation. Only graphitization of the iron surface at 700 °C after preceding carbon saturation at 1000 °C in CH₄? H₂ has an initially retarding effect. This study demonstrated possibilities of retarding the H₂S corrosion by Si or C which, however, are rather limited.     

Einfluß von Prüffrequenz und Salzgehalt des Korrosionsmediums auf die Korrosionsermüdung von Stählen bei betriebsähnlichen Lastabläufen

Influence of test frequency and NaCl-concentration on the fatigue life of steels under a realistic load sequence Because of the size and fatigue life of offshore structures the corrosion fatigue behaviour of those structures cannot be determined under service conditions. Also for the relevant corrosion fatigue tests in the laboratory using welded joints a compromise has to be found to reduce testing time to an economic justifiable amount. This compromise may be a higher stress used in the test, a higher test frequency or a higher concentration of NaCl in the seawater. The influence of test frequency and NaCl concentration on the fatigue life of fillet welded V-shaped specimens made from Fe E 355 KT was determined in artifical seawater and under a realistic load sequence. The fatigue life was separated into the crack initiation phase and the crack propagation phase as well. Mean frequencies of 0.2 Hz, 1.0 Hz and 10 Hz did not affect the fatigue life of welded joints until crack initiation, while low test frequencies of 0.2 Hz and 1.0 Hz accelerated the crack propagation. Higher NaCl-concentration of the seawater, however, had no effect on the fatigue life in both phases.     

Der Einfluß von Kupfer auf das Korrosions- und Passivierungsverhalten von Eisen-Chrom-Legierungen Teil II: Oberflächenanalytische Untersuchungen

The influence of copper on corrosion and passivation of iron-chromium alloys Part II: Surface analytical examinations The formation and the breakdown of potentiostatically in 1N H₂SO₄ generated passive layers of Fe/Cr alloys (7 resp. 11% Cr) and those with 1% Cu has been studied by XPS analysis and angular dependent XPS. After 1 h passivation the layer thicknes reaches 1 to 4 nm. In accordance with the current densities of layer formation the thickness is increased by copper and decreased by higher Cr contents. The mean thickness of the residual layers measured immediately after selfactivation shows the same tendencies. Passive layers have higher Cr- but lower Fe-contents than the alloys, especially in the presence of copper. Copper is only detectable in the metallic state. It causes raising amounts of γ-Fe₂O₃, leading to the assumption, that copper accelerates passivation via oxidation, of Fe-II-cations in the-oxide lattice by means of the initially existing Cu-II-ions. Concentration depth profiles show that the Cr-enrichment is localised at the oxide/electrolyte interface. Copper is somewhat enriched near the layer/alloy interface, resulting from the initial alloy dissolution. Self activation leads to strong enrichment of copper, raising from the lower to the upper part of layer. The ambivalent effect of copper in regard of improving passivation but accelerating self activation of FeCr-alloys in H₂SO₄ is discussed.     

Elektrochemische Untersuchungen zum Einfluß von Nitrat und Nitrit auf die Ausgangsruhepotentiale und den Kurzschlußstrom des Elementes Eisen/Zinn in Fruchtsäuren und -säften

Electrochemical investigations into the influence of nitrate and nitrite on the starting rest potentials and the short circuit current of the element iron/tin in fruit acids and juices With the aid of electrochemical measurements the influence is studied of nitrate and nitrite additions on the corrosion behaviour of tin and the iron/tin element in various fruit acids (citric, acetic, tartaric, malic and lactic acids) and vegetable and fruit juices; the results are compared with storage tests conducted in parallel. The electrochemical short time test is generally little suitable for showing the influence of nitrates, in particular because of the slow conversion of nitrate into nitrite which is a corrosion accelerator; the nitrite influence, on the other hand, can be shown quite easily since it produces on the one hand a potential shift toward more positive values and, on the other hand, gives rise to an increase in the short circuit current. These results can be applied to coated cans, too, where the nitrite gives rise to strong dissolution of iron with pitting attack.     

Einflüsse von Mo,V, Nb,Ti, Zr und deren Karbiden auf die Bindungszustände des Wasserstoffs in Eisen und das Bruchverhalten der Eisenlegieungen

Effects of Mo, V, Nb, Ti, Zr and their carbides on the binding states of hydrogen in iron and the fracture behaviour of the iron alloys Effects of Mo, V, Nb, Ti, Zr and their carbides on hydrogen permeation, diffusion, solubility and its distribution on different binding states in iron and iron based alloys are studied by use of the electrochemical hydrogen permeation technique. The results are analysed and described in terms of the trapping theory. The fracture behaviour of the alloys affected by hydrogen in different binding states are tested under constant elongation rate conditions. No essential specific effects of one of the alloying elements or their carbides are observed. Hydrogen diffusion and solubility, the total hydrogen content as well as the fracture behaviour are affected by the various microstructures of the alloys, thus only indirectly by the alloying elements. Crack initiation and fracture progress depend first of all on the external hydrogen activity and the grain size of the material, not on the total hydrogen content. Fine crystalline iron alloys of higher strength prove to be less sensible to hydrogen damage than coarse grain weak structures.     

Zur Prüfung von Schweißplattierungen mit austenitischen Bandelektroden der Art X2 CrNiNb 2413 auf Beständigkeit gegen interkristalline Korrosion

Testing of weld-claddings with austenitic band electrodes of the type X2CrNiNb24 13 for resistance against intercrystalline corrosion Two-phase, austenite- and ferrite-containing weld claddings of the 24 Cr-13 Ni-type may become susceptible to intercrystalline corrosion after heat-treatment in the 550°C temperature range due to a sensitization of the austenite. Thus, both austenite/austenite- and austenite/ferrite grain boundaries are attacked with the attack starting from the austenite phase in the latter case. Testing the resistance to intercrystalline corrosion in a sulphuric acid/copper sulphate media in the presence of copper turnings according to DIN 50914, the attack of grain boundaries ferrite/austenite becomes evident only if the specimens are bent after testing. Non-bent specimens do not show any indication of grain boundary attack by light-optical or even electron-microscopical metallographic examination. At non-bent specimens, the attack may become recognizable with considerably prolonged (several hundred hours) testing time. Referring to the investigations performed, the mechanism of intercrystalline corrosion of two-phase, ferritic-austenitic stainless steels and the influence of heat-treatment on susceptibility to intergranular attack are discussed.