Über den Einfluß von Schwefelwasserstoff auf die Korrosion des Eisens in sauren Lösungen

The influence of hydrogen sulphide on the corrosion of iron in acid solutions A considerable change of the polarisation behaviour of iron electrodes in acidic perchlorate and sulphate solutions was observed if they where saturated with hydrogen sulfide gas. H₂S markedly increased the anodic current densities and increases the corrosion rates by a factor of ten. The anodic Tafel slopes d log i_A/dE are only about half as steep as those in the absence of hydrogen sulphide. It is probable that the SH^?-ions behave as catalysts of the iron dissolution reaction in a similar manner as the OH^?-ions, but are adsorbed almost to saturation.     

Über den Einfluß der Kaltverformung von Stahl auf Wasserstoffaufnahme und -versprödung bei elektrolytischer Beladung

Effect of cold reduction of steel on hydrogen absorption and embrittlement during electrolytic charging The influence of cold work on hydrogen absorption in steel was studied using cold drawn wires. Hydrogen was electrolytically evolved at the steel surface and the absorbed amount analytically determined (hot extraction and gaschromatographic determination) The correlation between absorption time amount of absorbed hydrogen is shown in diagrams for different degrees of deformation by cold work. From these a mean diffusion coefficient is calculated. At low degrees of deformation (10-20% reduction by cold work) the saturation concentration of absorbed hydrogen (after 25 hours) is about 3 ppm. With increasing reduction the saturation concentration increases to a maximum of ca. 11 ppm (at 50%reduction). At still higher degrees of deformation (more than 60%reduction) the saturation concentration decreases again to about 4 PPm. For interpretation of these experimental results two different model hypotheses are discussed.     

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.     

Über den Einfluß des Gefüges von Zinklegierungen auf die Schutzfähigkeit von Zinkanoden in Seewasser

Influence of the structure of zinc alloys on the protective capacity of zinc anodes in sea water The use of zinc for cathodic protection duties in sea water is restricted because of the considerable polarisation of zinc. The behaviour is due in particular to cathodically active additions of lead, copper and iron. The microcouples then formed give rise to considerable zinc dissolution and to the formation of a thick and dense passivation layer. Since, however, any reduction of the iron content in zinc involves high cost it is more economical to add small quantities of Al, Cd, Si, Hg, Sn or Mn. These additions produce a considerable grain refinement and thus reduce the tendency to form microcouples even in the presence of iron.     

Einflußeiner Verzinkung auf die Korrosion von mit Zementmörtel beschichtetem Stahl in NaCl-Lösung

Effect of galvanizing on the corrosion of steel in concrete immersed in NaCl solution Galvanized or pickled steel sheet specimens were embedded in portland cement mortar of various water cement ratios and curing conditions and then wholly or partially immersed in 0.5 M NaCl solution for 1 to 5 yrs. Free corrosion potentials and electrical resistances have been measured. Immersion conditions and the presence of zinc have a significant effect on the corrosion resistance of the embedded steel sheets. The potentials of the wholly immersed specimens are very negative. Thus, these specimens cannot act as cathodes in corrosion cells, and the steel sheets within the mortar do not corrode. The partially immersed specimens, on the other hand, show very noble potentials. Also in the case of galvanized steel sheets the potentials are shifted to the same positive values in the course of exposure time. Thus, all these specimens can act as cathodes in corrosion cells. Localized corrosion generally occurs at the water/air line. In the case of pickled specimens the mortar is cracked due to growing corrosion products. In the case of galvanized steels the corrosion is retarded significantly. The test results are discussed in detail with respect to practical problems of cell formation, internal and external protection of pipes as well as the corrosion resistance of reinforced concrete.     

Untersuchungen über den Einfluß der Mikrostruktur auf die interkristalline und Kornflächenkorrosion von reinen Aluminium-Zink-Magnesium-Legierungen in 1 M Natriumchloridlösung

Investigation into the influence of the microstructure on the intercrystalline and grainphase corrosion of pure aluminium-zinc-magnesium alloys in an 1 M sodium chloride solution Potentiostatic polarisation tests of homogeneous pure aluminium-zinc-magnesium 2- and aluminium-zinc-magnesium 3-alloys as well as of a pure aluminium zinc-magnesium 3-alloy with two step ageing and quench-interruption treatments were carried out in an airsaturated 1 M sodium chloride solution at a temperature of 303 K. The pure aluminium-zinc-magnesium 3-alloy contents (weight percent): zinc 4,76; magnesium 3,00: impurities 0,08; balance aluminium, the pure aluminium-zinc-magnesium 2-alloy: zinc 4,60; magnesium 2,00; impurities 0,011; balance aluminium. The more negative breakdown potential in the homogeneous aluminium-zinc-magnesium-alloy than in the pure aluminium is caused by the zinc. According to the heattreatment the aged aluminium-zinc-magnesium 3-alloy shows above the breakdown potential grainphase corrosion and/or intercrystalline corrosion. In contrast to specimens with G.P.-zones or ν-precipitates in the matrix the specimens with ν′-matrix precipitates are grain-phase corroded along deep parallel streaks. This observation is attributed to the favoured formation of the ν′-precipitates on the (111)-planes in the matrix. The intercrystalline corrosion is more marked in specimens with a wider precipitate free zone, i.e. with a higher concentration of zinc and magnesium in the precipitate free zone.     

Über den Einfluß des aufgenommenen Wasserstoffs auf die Wechselbiegefähigkeit von Kohlenstoffstahl bei der Beizung in Schwefelsäure

Influence of hydrogen pick-up on the alternating bending strength of carbon steel during sulfuric acid pickling Steel coupons (St 3 GBKL) were acid-pickled in 1 M sulfuric acid at 50° C. The dissolution rate (by weight), the hydrogen uptake (by high temperature vacuum extraction and gaschromatographic determination) and the alternating bending strength (by alternating bending at 25 Hz and deflection angle ± 5°) were measured as a function of pickling time. The linear corrosion rate was 21 · 10^?6 · kg · m^?2 · sec^?1, the saturation concentration of hydrogen in steel was 8,76 ppm and the diffusion coefficient of hydrogen in steel was calculated as 8,74 · 10^?7 cm² · sec^?1. The number of bendings until fracture is not only a function of the integral hydrogen concentration, but is strongly influenced by the concentration profile of hydrogen in the sample; a hypothesis is given to explain this experimental finding.     

Über den Einfluß von Kohlenstoff und Stickstoff auf die Empfindlichkeit niedriglegierter Stähle gegen Spannungsrißkorrosion

The influecne of carbon and nitrogen on the sensitivity of low-alloyed steels to stress corrosion Application of stress to steels under the influence of certain media produces stress-corrosion cracking. This can be examined through experimental methods only, by which the specimens are kept under constant stress. The cracking time required for the specimen is then a measure of resistance of stress-corrosion failure. In this way it is possible to investigate the influence of alloying metals and the heat treatment on susceptibility of steels, by considering the respective strenght. Experiments were carried out to determine the effect of carbon content and the combined effect of carbon and nitrogen in a series of medium frequency and vacuum steels. It is found that increasing carbon content improves the resistance of specimens, taking also the higher strength into account. A higher nitrogen content shortens the cracking time. This shortening of resistance due to nitrogen content was much more note worthy in the case of high-carbon steels than in the case of low-carbon steels which were already sensitive in this respect. Comparing an open-hearth steel with the above steels, it seems as if there are other alloying metals which make the steels susceptible to stress-corrosion cracking. The effect of these alloying metals shall be investigated further.     

Über den Einfluß von Thioharnstoff und Thioharnstoff-Derivaten als Beizinhibitoren auf die Wasserstoffaufnahme,die Inhibitorwirksamkeit und die Wechselbiegefestigkeit von Kohlenstoffstahl bei der Säurebeizung

Influence of thiourea and its derivatives as pickling inhibitors on hydrogen pickup, degree of inhibition and fatigue load of carbon steel during pickling in acids The influence of additions of thiourea (TU), N-methyl-TU, N, N′-tetramethyl-TU, N-phenyl-TU, N, N′-diethyl-TU and N, N′-diphenyl-TU upon the acid pickling of mild steel (1,0 M H₂SO₄ at 50° C) was investigated. Measured were inhibitor efficiency, uptake of hydrogen and alternating bending strength of the samples as functions of inhibitor type and inhibitor concentration. With all inhibitors a maximum of inhibitor efficiency and alternating bending strength and a minimum of hydrogen uptake was found in the same inhibitor concentration range of about 0,001 M. Compared to pickling in pure sulfuric acid at this optimum concentration the inhibitor efficiency is between 95,2 and 98,4%, the decrease of the hydrogen uptake between 8,6 and 63,3% and the increase of the alternating bending strength between 20,0 and 43,4%, depending upon the kind of inhibitor. The alternating bending strength increases roughly linearly with decreasing hydrogen content of the samples. In the optimum concentration range the inhibitor efficiency and the alternating bending strength increase, the hydrogen uptake decreases roughly linearly with increasing adsorption area or increasíng molecular weight of the inhibitors.     

Untersuchungen über den Einfluß von Schwefelwasserstoff und Schwefeldioxyd auf die Korrosion chemisch beständiger Chrom-Nickel-Stähle in schwefelsaurer Natriumsulfatlösung

Investigations into the influence of hydrogen sulphur dioxide on the corrosion of chemically resistant chrome nickel steels in a sulphuric acid chrome nickel steels in a sulphuric acid solution of sodium sulphate By measuring the current/potential curves and determining the weight losses, the influence of H₂S and SO₂ on the corrosion of an 18/8 Cr? NI steel and of an 18/8 Cr? Ni stell with 2pCMo and 2.8pC Cu in sodium sulphate solution has been investigated. H₂S and SO₂ have the effect of shifting the rest potential towards the electronegative side, compared with a solution flushed with nitrogen, enlarging the potential range of active dissolution, and greatly increasing the dissolution, and greatly increasing the corrosion rate in the active zone. From the results of the measurements, it may be concluded that the metal dissolution is catalyzed by hydrogen sulphide ions and probably by reduction products of the sulphur dioxide. This catalyzing effect is not confined to the zone of activation overpotential but also occurs in the zone of the active plateau, the shape of which is largely determined by the migration phenomena. SO₂also has the effect of increasing the dissolution rate in the passive condition.     

Zum Einfluß der mechanischen Belastung auf die interkristalline Spannungsrißkorrosion von unlegiertem Stahl in Carbonat/Bicarbonat-Lösung

Effect of mechanical stress on intergranular stress corrosion cracking of unalloyed steel in carbonate/bicarbonate solution Intergranular stress corrosion cracking of a carbon steel in 0.5 M NaHCO₃ + 0.5 M Na₂CO₃ solution at 70°C was examined by normal, interrupted and cyclic CERT testing. Within the critical potential range, the lengths of intergranular cracks increase with increasing strain rate, and decrease when the material is cold worked. The fracture time indicates that the crack velocity increases with increasing strain rate. This is also observed with tensile specimens subjected to interrupted and cyclic strain rates. Detailed information on crack propagation and threshold stress levels can be obtained by interrupted and cyclic CERT tests. Intergranular cracks arise if surface region of the material undergoes plastic deformation in excess of a definite amount. In the case of a 60°-notch specimen the plastic zone must be greater than 0.3 mm. For cyclically strained specimens the crack velocity can markedly decrease with time or can become even zero as a consequence of strain hardening. From this one can conclude that stress corrosion cracking can only occur if stress levels are very high.     

Untersuchungen zum Einfluß von Inhibitoren auf die Wasserstoffversprödung von unlegiertem Stahl in Salzsäure

Investigations on the influence of inhibitors on hydrogen embrittlement of mild steel in hydrochloric acid The influence of four commercially available inhibitors as well as their main effective components on the corrosion behaviour of mild steel in 16 and 32% hydrochloric acid was investigated by potentiokinetic polarisation measurements, electrochemically controlled measurements of hydrogen permeation and by estimating the rate of mass loss. The inhibitors showed different, yet positive effects on the inhibition of the permeation of cathodically produced hydrogen. The best results were found with benzylchinolinium chloride as inhibitor. Particularly in acids containing hydrogen sulfide propargylalcohol turned out to be a poor inhibitor of hydrogen permeation. Under these conditions the addition of propargylalcohol to quart. ammonium salts even decreased their good effectiveness as single components. The fact that the effectiveness for the inhibition of hydrogen permeation often diminished in the course of short periods was not due to a simultanous increase of the corrosion rate.     

Über den Einfluß des Sauerstoffes auf die Korrosion in Dosenkonserven aus Weißblech

Influence of oxygen on the corrosion in tinplate cans The research was made with stell plate (thinnest plate, 0,07% C, from rimmed prematerial) and purest tin in a cell according to the galvanic element. Corresponding storages were made in unlaquered and laquered cans. Citrate buffer, pH 2.4, was used as electrolyte. Oxygen effects pitting corrosion on the steel surface. The corrosion activating effect connected with this pitting even then remins when oxygen is spent after some time of storage of cans. But the steel surface is protected simultanously by tin ions soluted from the tin surface, because these ions get adsorbed particularly on the endangered regions of the steel surface and inhibit the pitting corrosion. But this protection only happens in media where the steel plate is electropositive to tin. The question of the suitability of can filling free of oxygen therefore can not be answered in general, but has to be anwered individually taking into account the relations described.     

Über den Einfluß der Strömungsgeschwindigkeit und der NaCl-Konzentration auf die Sauerstoffkorrosion unlegierten Stahls in Wässern

Influence of flow velocity and sodium chloride concentration on the oxygen corrosion of unalloyed steels in water Corrosion of mild steel in aerated water normally leads to pitting, and to an enrichment of anions within the pits. Even HCO₃^? ions can support localized corrosion. The intensity of this is remarkably increased by chloride ions. In equilibrium water with Ca²⁺ and HCO₃^? ions and about 40 ppm free CO₂ protective rust layers are formed after about 500 hs exposure not depending on flow rate and salt concentration. These layers decrease the mean corrosion rate to about 0.1 mm/a, but do not prevent localized corrosion. Protective passive layers with extremely low corrosion rates are formed in flowing water with Ca²⁺ and HCO₃^? ions and about 40 ppm free CO₂. The minimum flow rate can be estimated for a 3/4 inch pipe to lie between 0.35 and 1.5 m/s. Investigations with water containing 40 ppm free CO₂ without Ca²⁺ at pH 4.7 and with NaHCO₃ (pH 7.2) show at low pH high corrosion rates – as expected –, and at pH 7.2 formation of protective layers with poor reproducibility in comparison with the situation in equilibrium water. Thus, Ca²⁺ ions support the protective properties of rust layers. HCO₃^? ions are necessary for the formation of protective layers because these are not formed in pure NaCl solutions.     

Über den Einfluß der Austenitstabilität von 18/8-Chrom-Nickel-Stählen auf die Verformungseigenschaften und auf das Korrosionsverhalten dieser Stähle

Influence of austenite stability of 18-8 Cr-Ni-steels on the cold working and corrosion properties of these steels The martensite formed during cold working has a negative effect on uniform corrosion only when the specimen is active in the particular medium; if so, corrosion current density increases with the degree of cold working. The martensite generated by cold working reduces on the other hand the susceptibility to intercrystalline corrosion and – in amounts up tn 2% – increases the time to failure in stress corrosion cracking (15 and 45 kp/mm²). The pitting potential is not shifted by the martensite, but pit density increases with the martensite content. In the Kesternich test no negative effect of the martensite is found. It is therefore concluded that reducing the Ni content in 18-8 steels improves workability without having a pronounced deleterions bearing on corrosion behaviour.     

Zum Einfluß von Chlorid-Ionen auf die Korrosion von unlegiertem Stahl in Wasserversorgungsanlagen

Considerations on the effect of chlorides on corrosion of unalloyed steel in plants for water supply The effect of anions of neutral salts, especially the chloride anions on corrosion of steel in tap water is discussed in terms of the theoretical aspects and explanations according to DIN 50 930 part 2. For a better understanding it is useful to separate the different corrosion effects: uniform corrosion attack, local corrosion attack and transfer of corrosion products into the water. With respect to these different effects test results are evaluated. It is shown, that neutral salts have no effect on uniform or local corrosion, whereas there is a marked effect of other water parameters. The transfer of corrosion products into the water is controlled by neutral salts as well as by alkalinity, pH, service conditions and the age of the plant.     

Untersuchungen über den Einfluß der Grundbeschichtung auf Elementbildung und Blasenanfälligkeit von mit Teerpech-Epoxidharz beschichtetem Stahl in Salzlösungen

Investigations into the influence of the priming coat on galvanic couple formation and bubble formation susceptibility of steel coated with tar-epoxy coating in salt solutions Unalloyed steel sheets with the surface conditions grit blasted, hot-dip and metal-spray galvanized, coated with 4 different primers have been top coated with coal tar-epoxy resin of 4 different thickness values. The specimens have been immersed in NaCl solutions for two years. Potential and coating resistance values as well as cell currents between the specimens and external steel electrodes have been measured. Finally the corrosion amount of the steel electrodes and of artificial holidays have been determined. The resistance values measured after 3–6 months are found essentially for the degree of corrosion protection. With decreasing resistance values the formation of blisters within the coating as well as the cell activity increase. Thus, steel at holidays and unprotected steel in contact with coated steel are anodically attacked. Excellent corrosion protection is given by coatings with coating thickness > 400 m?m as well as with Zn-epoxy or Zn-ethyl silicate primers, whereas sodium silicate is unsuitable.     

Über den Einfluß des Flächenverhältnisses auf die Stromdichte in galvanischen Zellen und Belüftungszellen

Influence of the area ratio on the current density in galvanic and aeration cells With a view to corrosion phenomena on conventional metal combinations the corrosion current density has been studied as a function of the cathode: anode area ratio in aeration cells (Fe/Zn, Fe/Fe, Zn/Zn, with Na-sulfate and NaCl as electrolytes) and in galvanic cells (Cu/Fe, Cu/Zn, with Cu? , ammonium and zinc sulfate as electrolytes). It was the aim of the investigation to find out the extent to which the theoretical ideas of Mansfeld and Akimov concerning film rupture and diffusion control may be applicable. It is found that mansfeld's concept must be extended to include the effective electrode potentials in order to allow an interpretation of corrosion current density in aeration cells. In the case of galvanic cells, however, there is a limitation attributable to the cell resistance which is determined by independent resistance measurements. The corrosion behaviour of the metals studied is interpreted in terms of the measured current densities.     

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.     

Ellipsometrische Untersuchungen zur Einwirkung niedermolekularer gesättigter Monocarbonsäuren auf Stahl in Luft hoher Feuchtigkeit

Ellipsometric investigations into the influence of low molecular saturated monocarbon acids on steel in air with high relative humidity The influence of formic and acetic acid in moist air on the corrosion of unalloyed steel (St 38 u 2) was studied with ellipsometric measurements. It was found that formic acid by low partial pressures p_f inhibited the corrosion as the result of adsorption on steel surface. On the other hand by p_f > 2,67 Pa and the relative humidity (RL) = 100% it was observed the formation of solid layer consist of corrosion products and formiate. Acetic acid favoured by low partial pressures in moist air the passivation of steel by means of oxygen in case the relative humidity (RL) < 80%. By (RL) ≥ 80% acetic acid is a stimulator of corrosion. Final the action mechanisms which at the time dominated by the different experimental conditions are discussed and conclusions about the effect of emission products from pine on the corrosion of steel in moist air are deduced.