Untersuchungen zur Korrosionsschutzwirkung von Teer- und Teerpech-Epoxidharz-Beschichtungen auf Stahl in Salzwässern bei kathodischem Schutz

Investigations on Corrosion Protection of Steel In Salt Water by Coatings of Coal-Tar Epoxy or Coal-Tarpitch Epoxy and Cathodic Protection Statistical evaluation of corrosion tests with coatings on steel combined from different primers and coaltarpitch- as well as coaltar-epoxy resins displays a good correlation between the susceptibility for blistering and decreasing values of the coating resistance as well as cathodic polarization. Furthermore, there is a small correlation with adhesion strength and the presence of holidays or defects in the coating. The population of blisters is mostly positioned near these defects which may depend on the coating procedure. The coating quality is determined by a proper coating procedure, a suitable primer or undercoat (no sodium silicate), a sufficient coating thickness (500 μm are preferred) and by a high-quality top-coat material (coaltar epoxy is preferred). In the case of application of cathodic protection the known conventional limit of the protection potential range (0.3 V more negative than the protection potential) should not be exceeded.     

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.     

Untersuchungen zum Einfluß des Stahlgefüges auf die instationäre Wasserstoffpermeation

Investigations on the influence of microstructure of steels on unsteady state hydrogen permeation The effect of microstructure of iron and a low alloyed steel on hydrogen permeation at room temperature is studied by means of the electrochemical permeation method. Hydrogen transport through these materials during charging or effusion processes is affected by microstructural heterogeneities and hydrogen content. The diffusivity as a function of the state of the materials ranges over about five orders of magnitude. In course of non-steady state diffusion dislocations and interfaces decrease the effective diffusivity to values between 10⁻⁷ and 10⁻⁹ cm²/s. At steady state permeation the diffusivity reaches the values of 10⁻⁵ to 10⁻⁴ cm²/s.     

Untersuchungen zum Einfluß des Stahlgefüges auf die stationäre Wasserstoffpermeation

Investigations on the influence of microstructure of steels on steady state hydrogen permeation The effect of microstructure of iron and of a low alloyed steel on steady state hydrogen permeation is studied by means of the electrochemical permeation method adapted to hydrogen gas phase charching at p = 1 bar in the temperature range of 15 to 80 °C. In case of pure annealed iron the permeation coefficient is given by Impurities, oxide inclusions and a high density of lattice defects do not affect steady state hydrogen permeation remarkably. In steel specimens of different microstructure (pearlitic, martensitic, bainitic) hydrogen permeability is decreased by a factor 4 to 8. Carbide precipitates in tempered martensite do not change the permeation coefficient. Also cold deformation by rolling to about 15% shows no effect on steady state permeation. Cold rolling to about 40% or higher degrees decreases the steady state hydrogen flux considerably. In all cases, no essential change in temperature dependence is observed.     

Anwendung der Elektronenmikrosonde zur Untersuchung des Einflusses der Oberflächenvorbehandlung auf den Verlauf der Phosphatierung und der elektrophoretischen Beschichtung

Application of the electron microprobe to the investigation of the influence of surface pretreatment on the progress of phosphatation and electrophoretic coating A general discussion is presented of the possibilities available for analyzing micro regions on solids with the aid of the microprobe. Along the same lines a survey is presented concerning the range of applications of this method of analysis in connection with the chemical pre-treatment processes of metal Surfaces. The principle of action of the electron microprobe, the method of analysis and the specimen preparation are dealt with. It is shown, that the electron microprobe is a useful means for studying the influence of pretreatments on the structure and formation of phosphate and organic coatings. In the case of the analysis Of the phosphating process, however, the can be interpreted more easily when supplemented by results of X-ray structural analysis. The distribution of Fe, P, Mn, Zn and Ni across the section of the coating has been determined and a hypothetical mechanism of phosphating has been formulated thereupon; the ac-of Ni²+ ions has been explained as well. It has been shown, that components of the substrate as well as of the coating are dissolved during the electrocoating process and are incorporated in the organic coating. This process has a great importance with respect to colour and protective properties of the coatings and with respect to the turn-over of the electrolyte.     

Untersuchungen zum Einfluß von Sulfid- und Sulfationen auf die Korrosion des Eisens in alkalischer Lösung

Investigation into the influence of sulfide and sulfate ions on the corrosion of iron in alcaline solution The corrosion behaviour of Armco iron as well as that of a technical high-strength steel was investigated in sulphide - and sulphate-containing electrolytes of pH ～ 12.6. Current density - potential curves show that iron, after successful passivation, remains passive and protected against corrosion in a solution saturated with CaS, CaSO₄ and Ca(OH)₂ at potentials up to 800 mV(EH). Passivation experiments conducted by changing from the active region to various anodic potentials yielded a critical potential region around 300 mV(EH), above which corrosion appeared. Up to E_H = 200 mV complete passivation was observed. The same critical potential region was observed in experiments of repassivation after mechanical damaging of a protective passive layer. Additional tensile stresses of 85%· σ_0,2 caused no stress corrosion cracking at a potential of 500 mV(EH). After damaging the passive layer, through scratching of the stressed wires fracture occured at and above potentials of 300 mV(EH). At 200 mV(EH) repassivation was observed even under tensile load. In a sulphate-free Na₂S/Ca(OH)₂ solution of the same sulphide ion concentration no stress corrosion cracking of the samples occured at any potential up to 800 mV(EH) even after scratching the steel samples. The observed stress corrosion in sulphide - and sulphate-containing electrolytes is to be ascribed to the action of sulphate and not to sulphide ions.     

Wirkung von schwefelhaltigen Inhibitoren auf die Korrosion von Messing 63/37 in Trichloressigsäure

Action of sulphur containing inhibitors on the corrosion of 63/37 brass in trichloroacetic acid Trichloroacetic acid is highly corrosive to brass. Sodium thioglycolate, sodium diethyl dithio carbamate and carbon disulphide have been studied as corrosion inhibitors for brass (63/37) in trichloroacetic acid. The inhibitive power of sulphur-containing organic compounds is due to chelate formation, the chelate adhering strongly to the metal surface. The efficiencies of above stated inhibitors were found in the following order: .     

Ellipsometrische Untersuchungen zur Einwirkung von Luft unterschiedlicher Feuchtigkeit auf unlegierten Stahl

Ellipsometric investigation into the effect of air with various relative humidities on unalloyed steel The thickness of the oxide film formed on the surface of unalloyed steel (St 38) in dry air has been measured with adequate precision by ellipsometric techniques: it amounts to 3.5–4.5 nm. It could be shown in addition that the thickness of this primary oxide increases as the relative humidity is increased. It was possible to show that for any given value of relative humidity there exists a stationary oxide film thickness which depends on the roughness of the substrate surface. The ellipsometric measurements have further shown that during exposion to moist air, water becomes adsorbed to the oxide film; the extent of adsorption depends on the thickness and the composition of the oxide layer.     

Untersuchungen zum Einfluß des gelösten Siliziumdioxids auf die Korrosion von Chemieemail in Salzsäure

Investigations on the Influence of Dissolved Silica on the Corrosion of Chemical Service Glass Enamel in Hydrochloric Acid At high temperatures chemical service glass enamel is being attacked by mineral acids more than expected in regard to the ion exchange theory. Taking as an example the corrosion test results of a glass enamel in 20% hydrochloric acid at 140 °C one can demonstrate that under adverse conditions all glass constituents will be dissolved almost equally during attack. This result is surprising in respect to the glass component silicon-dioxide, however, its solubility in the acid is increased to 70 ppm by the high temperature. This limit essentially determines the degree of the acid attack on the enamel. If the silica concentration of the attacking acid is low and fairly low amounts add because of short reaction times or high volume to surface ratios then the corrosion rate will be high. If the attacking acid already contains higher concentrations of silica the glass enamel corrosion will be strongly inhibited. On the basis of the quantitative results it is possible to recommend a procedure for testing glass-linings at 140 °C in 20% hydrochloric acid. For this application, too, the corrosion situation in the vapor phase and liquid phase of a technical size chemical reactor is being discussed.     

Beitrag zum Problem des Einflusses von Silicium,Stickstoff und Bor auf die Verzunderungsbeständigkeit und Warmfestigkeit austenitischer Chrom/Nickel-Stähle

A contribution to the problem of the influence of Si, N and B on the scaling resistance and high temperature strength of austenitic CrNi steels Laboratory and field rests (up to 5000 hrs in an enamelling stove) into the scaling behaviour of alloyed steels, with a particular view to a possible reduction of the Ni content. From the steels – Cr23Ni18, Cr25Ni20Si2, Cr23Ni13, Cr23Ni13Si2, Cr23Ni13Si2N and Cr23Ni13Si2B – the type Cr25Ni20Si2 has the highest, Cr23Ni13 the lowest oxidation resistance. Addition of Si has a negative effect, in particular on creep resistance at high temperatures, while oxidation resistance is improved. In cases of simultaneous thermal and mechanical loads boron additions are preferable. In cases of alternating temperature changes under mechanical stress alloying with nitrogen appears most promising.     

Untersuchungen über die auf Eisen durch Permanganat erzeugte oxidische Passivschicht

Investigations into the oxidic passive layer produced on iron by permanganate By means of potential measurements on iron electrodes which was passivated by permanganate, and by application of the radiotracer technique the conditions of layer formation could been optimized. From stabil formed layer electrodes the electrode reaction and by registration of the drift of pH value during the immersion in unbuffered electrolyte solutions the isoelectric range of their outside layer component was determined. The galvanostatic cathodic reduction of the layer additional informations about the existence of several layer components was obtained. On the basis of this experiments a model to the qualitative composition of passive layer which formed on iron in permanganate solutions is suggested.     

Kurzzeitprüfmethoden zur Untersuchung des Einflusses von Wärmebehandlung und chemischer Zusammensetzung auf die Korrosionsbeständigkeit martensitischer Chrom-Nickel-(Molybdän)-Stähle mit tiefem Kohlenstoff-Gehalt

Short-duration test for evaluating the influence of heat-treatment and chemical composition on the corrosion resistance of low carbon martensitic chromium nickel (molybdenum) steels The following procedures were examined and compared for their suitability as rapid corrosion tests in comparative investigations on the influence of heat treatment and other production parameters on martensitic chromium-nickel-(molybdenum) steels of low carbon content:

• –Measurement of the mass loss in boiling 20% acetic acid, and in some cases 5% nitric or 1% hydrochloric acid.
• –Immersion in sulphuric acid/copper sulphate solution (modified Strauss test).
• –Current density/voltage curves in 1 N sulphuric acid.
• –Measurement of pitting potential und activation pH in 3% sodium chloride solution (on limited scale).

The test materials employed contained 0.032–0.082% carbon, 11.6–16.4% chromium, 3.8–5.9% nickel and 0.31–1.6% molybdenum. The most suitable testing procedures were selected according to the steel type. Up to a mass loss rate of ≥ 0.05 mg · cm^?2 · h^?1 (materials with resistance inferior to steel type 13-6-1) the acetic acid test provides an excellent basis for comparison. Provided the optimal testing temperature is adopted, current density/voltage curves and immersion in sulphuric acid/copper sulphate solution yield usable results with all steel types investigated. The value of the information yielded by the test procedures is generally enhanced by metallographic characterization of the corroded surfaces; in particular the localization of chromium-depleted structure zones is made possible by this.     

Einfluß des Chloridgehaltes in Trinkwasser auf die Korrosion von unlegiertem Stahl

Influence of chloride content in tap water on the corrosion of unalloyed steel Regarding the effect of neutral salts in tap water on the corrosion of unalloyed steel, little data is available, some of it being contradictory. This applies in particular to chlorides. In the present paper, disks rotating at velocities of from 0–2000 min⁻¹ and pipes through which tap water flows have been used to investigate, for various water supplies (Ludwigshafen, Leverkusen and Berlin tapwater) and as a function of the chloride concentration (0.28–15.5 mol m⁻³) and of the test period (up to 10 000 hours), the area-related linear rates of loss in weight, the fractional corroded surface areas, the through depths and pit depths, and the distribution of elements in the surface layers.     

Untersuchungen über die Einflüsse auf Stromdichte-Potential-Kurven und ihre Reproduzierbarkeit

Investigations into factors having a bearing on current density vs. potential curves and their reproducibility The shape of potentio-kinetic current density/potential curves enables conclusions concerning the corrosion behaviour of a material to be drawn only when the reactions taking place at the surface of the material are known, and when initial potential, holding time prior to potential variation and potential feed are taken into account. Experimental work with Pt in tap water, 0.5 N KCl and 5% H₂SO₄ has revealed primarily a relation between initial potential and current density in the regions of hydrogen ionisation and adsorption. The holding time preceding potential variation comes to bear in water and H₂SO₄ primarily in the hydrogen adsorption region, in KCl, however, in the oxygen adsorption region. Increasing potential feed results in increasing limiting diffusion current, the trend being parallel to that of current density changes.     

Untersuchungen zur Einsetzbarkeit elektrochemischer Rauschmessungen zum Studium des Korrosionsverhaltens von Kupferrohren in Trinkwasserinstallationen

Investigations on the applicability of electrochemical noise analysis to study the corrosion behaviour of copper tubes in potable water installations Experimental evidence is given for the system copper/potable water that the electrochemical noise analysis (ENA) can be successfully applied to monitor the corrosion intensity at copper surfaces with appropriately adapted measuring systems. Medium and materials surface effects on corrosion can be identified in the signal pattern of both potential and current noise. ENA is applicable under stagnation as well as under flow condition.     

Impedanzspektrometrische Untersuchungen zur Wirkungsweise von Inhibitoren und Tensiden bei der CO2-Korrosion von Stahl unter Erdgasförderbedingungen

AC impedance investigations on the performance of inhibitors and surfactants in CO₂ corrosion of steel under natural gas production conditions Inhibition mechanisms of CO₂, corrosion of low alloy carbon steel (38 Mn 6) were studied under production conditions of sweet natural gas (1 M NaCl + 0.1 M CaCl₂; 1 and 5 bar CO₂; 80°C) in the presence of surface active compounds (inhibitors, surfactants) with AC impedance spectrometry. Based on a pore model an equivalent circuit was developed which explains the action mechanisms of the substances tested. Fatty amines and imidazolines inhibit the interface reaction at the bottom of pores in the corrosion product scale due to adsorption. Nonionic surfactants can impair the effectivity of N-containing inhibitors. 1-Octyne-3-ol acts through formation of polymer films and reduces the porosity of the scale. All substances under investigation influence the morphology of the scale and the kinetic of its formation.     

Einfache Methode zur potentiostatischen Bestimmung des Lochfraßpotentials in einem einzigen Versuch

Simple method for the potentiostatic determination of teh pitting potential in one single experiment A simple and fast method is described for the determination of the pitting potential of stainless steels. By using wire electrodes to which a constant DC-potential is applied one may scan potential ranges of any size in one single experiment. Tests with four autenitic steels in 1 N NaCl have shown that addition of Mo and Si displaces the pitting potential to higher values at room temperature; at higher temperature, however, this effect vanishes. Addition of NaBr and NaJ to the NaCl-solution produces a considerable increase of the pitting potential of Mo-free stainless steels. The experimental principle can be used also for the investigation of stress corroison cracking.     

Einfluß einer Feuerverzinkung und PVC-Beschichtung von Bewehrungsstählen und von Inhibitoren auf die Korrosion von Stahl in gerissenem Beton

Influence of galvanizing and PVC-coating of reinforcing steels and of inhibitors on steel corrosion in cracked concrete Cracked concrete beams of concrete quality B15 and B35 with carbonized cracks were exposed in artificial seawater, under frost and deicing salt conditions and in industrial climate. The reinforcement was composed of black steel, galvanized and PVC-coated steel. For the purpose of additional protection the concrete was partly mixed with an inhibitor Ca(NO₂)₂. The concrete cover was 1,5 till 5,0 cm. It was found that the inhibitor protects satisfactorily only in the case of the higher concrete quality, cover 1,5 cm and not to high crack width. A protective effect of galvanizing is given by not to high chloride contents (< 1,5% relative to cement) and crack widths. The chosen PVC-coating failed because of chemical instability in the alcaline medium concrete.     

Der Einfluß des Gefügezustandes auf die Oxydationseigenschaften von Zirkonium-Vanadium-Legierungen

Influence of structure on the oxidation behaviour of zirconium vanadium alloys The oxidation of the alloys ZrV 1 and Zr V 3 has been studied on a comparative basis to zirconium after various mechanical and thermal pretreatements; the aggressive medium was steam of 300°C.It has been shown that recrystallizing annealing after cold deformation has but little influence on the oxidation resistance; a considerable diminution of the oxidation susceptibility has been achieved, however, by grain refining after a cold deformation or annealing of the martensitic structure. This type of treatment has a positive effect in particular on the structure of the protective layer. In view of the fact that the oxidation susceptibility increases with the concentration of the alloying element it may be suggested that the intermetallic compound ZrV₂ has a negative effect. Consequently, the oxidation resistance is improved by quenching from high temperatures which prevents the formation of segregations.