Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen I. Verhalten gegenüber wäßrigen Medien

Investigations into the corrosion behaviour of zirconium alloys I. Behaviour in the presence of aqueous media Extensive corrosion research covering 5O Zr alloys have shown that the good corrosion resistance of pure Zr cannot be improved to any greater extent by alloying. Pur Zr as well as most of its alloys have a high corrosion resistance; even in boiling mineral acids (20% H₂SO₄, HNO₃, and HCl) the corrosion rate is below 0.5 g/m²·d and no attack can be recognized in neutral salt solutions. The metal also resists attack by boiling 2O% KOH. Strong attack, however, it caused bv Fe-III-chloride. The metals do not resist attack by HF, while neutral KF attacks but little, however produces pitting. The effect of alloying additions is due to the structure produces by them: pure grain boundaries or very fine heterogeneous structures show good corrosion resistance. Ti, Hf, Sn and small amounts of Nb have little influence, Mo, W, larger amounts Nb and small pt and Re additions give rise to Local cells, while Fe, Cr and Ni have practically no influence.     

Untersuchungen zum Verhalten von Aluminium bei kathodischer Polarisation

Investigations into the behaviour of aluminium under cathodic polarization Characteristic discontinuities in the cathodic current density-potential curve (traced for high purity Al and Fe-containing Al in buffered Na-chloride solution), relations between the current density and the inflexion point of the curve and the buffer capacity of the electrolyte, as well as the heavy corrosion observed above a critical current density yield the conclusion that a cathodic rupture occurs because of the alkaline reaction of the liquid boundary layer. The cathodic reaction is thereby transferred from the oxide-solution boundary to the metal-solution boundary and the formation of hydroxide takes place not by direct hydration, but via hydroxo complexes which are precipitated at the electrode because of the pH prevailing there and then block the electrode. In the case of the Fe-containing Al there is an enrichment of Al₃Fe which results in increasing hydrogen evolution at constant potential.     

Verhalten von Sintertonerde gegenüber Metallsulfiden und H2/H2S-Gasgemischen

Behaviour of sintered alumina in the presence of metals, sulfides and H₂/H₂S gas mixtures For an investigation into the formation of nonstoichiometric iron sulfide phases an experimental apparatus has been designed the hot zone of which is stable between 300 and 1300°C and resists hydrogen, hydrogen sulfide, solid and molten metals and their respective sulfides. The crucible was made of high purity sintered alumina which is stable up to 1400°C. After each experiment the crucibles were washed in HCl and heated to red heat; they could be used repeatedly up to their accidental breakage.     

Verhalten von thermoplastischen Kunststoffen gegenüber aggressiven Medien – Einfluß der Morphologie am Beispiel von Polyethylen hoher Dichte

Behaviour of thermoplastic materials in aggressive Media – Influence of morphology on the example of high density polyethylene To a certain degree the morphology of thermoplastic intermediate products can be influenced either by using different fabrication techniques (molding, extrusion) or in case of a special technique e.g. by varying the cooling conditions. Plates and pipes produced from unpigmented PE-HD granule of a certain batch, differing in morphology only were exposed to a physically active medium (p-xylene), a chemically active medium (50% chromic acid) and a surface-active medium (2% wetting-agent). Apart from immersion-tests at varying temperatures creep-experiments on plates under constant load were carried out. The registered differences in sorption, creep-compliance, cracking etc. are discussed in context with the different morphological structures (e.g. crystalline phase).     

Untersuchungen über das Korrosionsverhalten von Zirkoniumlegierungen II. Verhalten bei Wasserdampfkorrosion

Investigation into the corrosion behaviour of zirconium alloys. 11. Behaviour under steam corrosion conditions An investigation into the corrosion behaviour of about 50 Zr alloys in high pressure high temperature steam (240 atm, 400°C) and hot air (4OO°C) has revealed a clear correlation between the behaviour in the two media. Alloys characterized by lower scaling susceptibility are also less susceptible to corrosion in steam, while, on the other hand, thicker scale layers tend to reduce hydrogen embrittlement. From the alloying additions studied Sn, Fe, Cr and Ni have a clearly favourable influence and W may have a similar effect. Ti has an outspoken negative influence on the behaviour in steam (spalling off of the scale) and Si, too, is deleterious because the SiO₂ being formed is soluble in steam, so that the scale layers retain their penetrability. Mo cannot be recommended either, while Nb is favourable in particular because of its grain refining effect. The favourable effect of Cu additions has been confirmed. Alloys with Fe, Cr and Ni and single types with Mo, Nb and Cu are superior to pure Zr with respect to steam resistance and are in part superior to Zircaloy 2 with respect to their mechanical strength.     

Untersuchungen zum Korrosionsverhalten von AlLi-Legierungen

Corrosion behaviour of aluminium-lithium alloys The AlLiMgCu alloy 8090 was studied in its texturated fine grained version “A” and in its recrystallized coarse grain structured version “C” in different artificially aged conditions in reference to several other AlLi alloys, each in its heat treatment condition of practical interest, and to the convetional alloy 2024 T3. The subject of research was the general corrosion behaviour of semifinished AlLi products, particularly sheet material, under alternate and permanent immersion conditions in neutral 3.5% sodium chloride solution; the stress corrosion behaviour was studied under constant load in the long transverse direction according to ASTM G44 and G49. The underaged conditions, which are the relevant conditions for technical application of the 8090 “A” and “C” sheets, showed an approximately equivalent or even better corrosion behaviour in comparison to the lithium-free alloy 2024 T3 in the corrosion tests with unloaded specimens. The threshold above which the AlLi alloy 8090 in some heat treatment conditions is attacked by stress corrosion cracking within the 30 days lasting constant load test depends on alloy composition, testing direction, grain size, stretch-forming, artificial ageing condition, surface pretreatment and the specimens' dimensions.     

Untersuchungen zum Emaillieren von Nickelbasislegierungen

Investigations concerning glass lining of nickel base alloys Frequently, handling of highly corrosive products requires the selection of glass-lined equipment in chemical engineering. Normally, carbon steel or low-alloy steel for elevated temperature application is used as base metal. The experience shows, however, that in case of any damage to the glass-lining the base metal will corrode rapidly, thus necessitating an immediate shut-down. Since extreme demands for equipment availability may require a failure-tolerant performance of the equipment I-gal-autoclaves built from various nickel-base alloys were lined with different glass-types and investigated for service performance, especially with regard to mechanical and resistance properties. The paper summarizes the results.     

Zum Einfluß von Heißgaskorrosion auf die Haltbarkeit von Hochtemperaturwerkstoffen

Influence of hot gas corrosion on the life of high temperature materials The study of gas turbine materials shows that behaviour is influenced by stress corrosion cracking even in the creep range. The creep strength is reduced at 1000 °C by 20–50%, depending on the salt concentration in the gas. The influence of the salt concentration is negligible only ≤ 1 ppm salt and then it is possible to base calculations on creep data obtained in air. The influence of hot gas corrosion is particularly critical between 800 and 1000 °C. The influence of general corrosion can be neglected.     

Die Erosionsbeständigkeit von Kupferwerkstoffen gegenüber strömendem Wasser

The erosion resistance of copper base materials in flowing water Following a review of work done so far the erosion resistance of the most common copper tube materials is subjected to a comparative test in a model experiment simulating practical conditions. The apparatus (for simultaneously testing 9 specimens) has been fed with well water which practically contained no solid matter; The water velocity was about 0.5 m/s, the duration of the test more than one year. With smaller tube diameters the zones at the beginning of the tube show serious attack; as to the arrangement according to resistance the following picture is obtained: copper and CuZn30 are practially equivalent, while the ternary special brasses are clearly superior; CuNi10Fe is by far the best material, while CuNi5Fe corresponds about to common special brasses. Aluminium brasses are considerably inferior even to Cu. A striking fact is, that in the case of CuNi10Fe the attack does not at all seem to depend from the flow velocity.     

Untersuchung von Säureinhibitoren hinsichtlich ihrer Wirkung gegenüber H-induzierter Korrosion

Investigation of Inhibitors Regarding Weight Loss Corrosion and Hydrogen Absorption in Acids It is theoretically shown that a relationship between inhibition of weight loss and hydrogen induced corrosion cannot be generally expected. Ten commercial inhibitors for pickling and sour gas service have been investigated. A correlation between the two kinds of corrosion mentioned above does not exist. In all cases the inhibitors were found to decrease the hydrogen absorption rate. This effect depends on the medium without any correlation. From these results one cannot compare inhibition of weight loss corrosion with that of hydrogen absorption. Furthermore, an inhibition of hydrogen-induced corrosion phenomena (HIC, HSCC) can only be evaluated by permeation measurements under service conditions.     

Beitrag zum physikalischen und korrosionschemischen Verhalten von IVa-Metallegierungen

The physical and corrosion-chemical behaviour of IVa metal alloys The stability of titanium in respect of non-oxidant acids can be considerably increased by alloying it with Zr, Hf, Nb, Mo or Re. In the case of Zr, Hf, Nb and Ta, a decisive improvement of the corrosion behaviour can only be attained if the At-percentage of these metals in the alloys exceeds 50 pC. In the case of molybdenum, a content from 20 pC upwards has already a markedly passivating effect. But the improvement in corrosion properties must be bought at the price of poorer machinability. A particularly effective alloying metal, even in small quantities, is Rhenium. An excellent corrosion resistance and, at the same time, good machinability can be attained with ternary Ti-Mo-Ta alloys (with Mo + Ta accounting for some 20 At-pC) and with a Ti-12Mo-1Re alloy. The alloying of titanium with Zr, Hf, V, Cr or Mo is apt to cause, in some cases, a considerable deterioration in the scaling resistance of titanium. Improvements can be obtained by using small quantities of Nb, W and particularly Ta. Ti-Ta alloys with Ta contents up to 10 At-pC still have a good scaling resistance at 900° C.     

Untersuchungen über das Kleben von Blei

Investigations into adhesive lead joints Lead plate thoroughly prepared for adhesive joining can be connected with other materials with the aid of resin-based adhesives. Picked surface yield higher strengths in the adhesive joint than do surface roughened by mechanical action. Hot-curing epoxy-based adhesive on picked surface yield adhesive strengths superior to the cohesive strength of lead as established in the tensile test. Adhesives requiring high compressive loads for curing, or adhesives based on vinyl resins are not suitable for use with lead. Overlapping joints may neutralize just small fractions of the tensile shearing forces. In such cases lead will become detached from the adhesive layer because of its high degree of deformation. At elevated temperatures, however, the adhesive strength of the adhesive on lead is often superior to the shearing strength of the joint; as a consequence thereof, the lead itself will fail. Adhesive joints with lead can bear temperatures up to 70°C for a long time without any loss of strength. Glass fibre roving embedded in the adhesive layer may increase the tensile strength and yield advantages as far as processing technology is concerned. Lead-coated parts may be deformed even after adhesive joining.     

Einzelergebnisse aus laufenden Untersuchungen zum Verhalten von Kupferrohren in Trink- und Brauchwässern und Darstellung des neuesten Standes der Gesamtschadensentwicklung von Kupferrohren

Individual results from current research into the behaviour of copper tubing in potable and industrial waters, and presentation of the most recent state of overall failure evolution of copper tubes The number of corrosion failures, in particular in cold-water systems has decreased despite increasing use of copper as tube material; this fact is attricuted to improved manufacturing techniques. On the other hand it has not been possible to elucidate the mechanism of another type of corrosion sometimes encountered in water of higher temperatures, because in this case the freedom of the surface from carbon films does not seem to be a decisive factor. While in the case of cold-water systems pitting with pits being covered by corrosion products (carbonates, at the pit base chlorides) is the characteristics aspect, pronounced formation of surface layers is encountered in the warm-water systems, the layers being of very variable thickness and covering single pits. In this case the water composition seems to be a dominating factor.     

Vergleichende Untersuchungen über die Aufstickung von niedrig- und hochlegierten Stählen sowie der Legierung NiMo 16 CrW in Ammoniak bei 300 bis 500°C

Comparative investigations into the nitruration between low and high alloy steels and the alloy NiMo 16 CrW in ammonia at 300 to 5OO°C The nitriding behaviour of high temperature high strength steels 13 CrMo 44, 10 CrMo 910 and 17 CrMoV 10, of the high alloy high temperature strength steels X 8 CrNiNb 16 13, the stainless steel Y 8 Cr 17 and nickel base alloy NiMo 16 CrW has been studied in ammonia at 300, 400 and 5OO°C, test durations being up to 1000 hours. The evaluation was based on determination of the nitriding depth preferentially with the aid of microhardness measurements. The structure of nitride layers and the structure changes due to nitrogen adsorption in the material are explained in connection with the time dependence of nitriding. The behaviour of specimens Passivated in air is shown as well as the influence of the surface pretreatment by depassivation or preoxidation and the influence of minor oxidising constituents (air, steam) in ammonia.     

Untersuchungen zum Einfluß von Polyphosphat auf das Korrosionsverhalten von Kupfer in Elektrolytlösungen

Experiments on the effect of polyphosphate on the corrosion behaviour of copper in electrolytic solutions Gravimetric experiments in a circulating equipment were performed on the effect of Graham salt on the corrosion behaviour of copper in electrolytic solutions by means of a high confounded 2^7?4-fractional factorial. The composition of copper samples: 99.7% Cu, 0.002% Bi, 0.005% Sb, 0.01% As, 0.05% Fe, 0.2% Ni, 0.01% Pb, 0.05% Sn, 0.01% S. The aqueous electrolytic solutions contained hydrogencarbonate-, sulphate-, chloride-, nitrate-, manganese-, calcium ions and Graham salt. It appears that Graham salt is unsuitable for the inhibition of copper corrosion. The polyphosphate promotes corrosion. Chloride-, nitrate-, sulphate- und manganese ions also increase corrosion rate whereas it is decreased by hydrogencarbonate ions. Increase of temperature also causes a decrease of corrosion rate. An existing danger of contact corrosion induced by copper cannot be removed by addition of Graham salt if copper and carbon steel, respectively galvanized steel are installed together in equipments of plant water.     

Metallurgische Erkenntnisse aus dem Verhalten von Schweißnähten an unlegierten Stählen gegenüber Korrosion durch verdünnte Laugen und fließendes Meerwasser

Metallurgical conclusions drawn from the behaviour of welds in unalloyed steels toward corrosion by diluted alkaline media and flowing sea water The resistance of welds of unalloyed and low alloy electrodes in contact with alcaline media and flowing aerated sea water increases with the ratio Mn:Si. This ratio should be > 2.4, in this connection, Cu contents should be > 0.3% and the Ni:Cu ratio > 1. Traces of P and As increase the resistance of CrMo low alloy electrodes in alcalic media and of unalloyed acid electrodes in sea water.     

Elektrochemische Untersuchungen zum Korrosionsverhalten von Duplexgusswerkstoffen in Rauchgasentschwefelungsanlagen

Electrochemical investigations on the corrosion behaviour of duplex cast stainless steels in flue‐gas desulphurisation plants This paper deals with results from corrosion examination on duplex cast stainless steels from original components in the flue‐gas desulphurization (FGD) of the VEAG‐power stations Boxberg III and Jaenschwalde under practice and laboratory conditions. In practice the mentioned components have a better corrosion resistance in the FGD medium of the Boxberg power station. The same results were obtained by laboratory examinations, getting a shift in critical potentials of a few hundred millivolts. The tests in a by‐pass of the FGD confirm these results in tendency. However, partially significant differences to laboratory examinations were established on specimens with pre‐damaged original surfaces. This can be traced back to the more severe test conditions in the FGD, like solids and flow. The repassivation behaviour of the materials under investigation was examined by means of electrochemical noise analysis. The values of the free corrosion potentials in the Jaenschwalde power station were higher than potentials, necessary for a safe repassivation of occurring pits. This cause the failures on the components. Remedy steps are discussed in this paper in detail. The free corrosion potential in the Boxberg power station is about 200 mV below the repassivation potential. Because of that, short‐time fluctuations of system parameters leading to enhanced corrosion risk can be tolerated.     

Über das korrosive Verhalten von Eisen in Essigsäure

The corrosion behaviour of iron in acetic acid Experimental investigation with Armco iron in oxygen-free sodium acetate and sodium chloride acidified with acetic and hydrochloric acid respectively; the reaction is assumed to be under cathodic control. According to results obtained so far both acids may function as proton donators; the activation energy for proton formation from acetic acid is probably lower. Proton donations by acetic acid is further enhanced by adsorption of acid molecules to the metal surface. On the other hand the adsorption effects may be compensated by too low a conductivity of the solution. Complex formation by acetate ions seems to play a minor role. As to the mechanism of the corrosion studied the Volmer reaction is assumed to be the partial reaction subject to the most pronounced deceleration; this reaction is divided into two steps, a dehydratation of the proton with pronounced activation hindrance, and subsequent extremely fast breakthrough reaction.     

Untersuchungen zum Umwandlungsverhalten von InSn-Legierungen bei selektiver Korrosion

Investigation of phase transformations induced by the selective dissolution of In from InSn alloys . In the context with the theory of dealloying the selective dissolution of In from InSn alloys has been investigated. As a consequence of their low melting-point the corrosion behaviour of these alloys differs significantly from the behaviour of higher-melting alloys. For the β-InSn phase this is illustrated by the result that a Sn-content of 20 at.%, supported by a porous morphology of the γ-SnIn product phase, does not excert a significant influence on the In-dissolution kinetics. Selective dissolution of In from γ-SnIn and from the β-Sn terminal phase is controlled, however, by solid-state diffusion of In to the electrode surface. Under these circumstances the product phase β-Sn that results from the removal of In from γ-SnIn at room temperature grows with a morphological stable interface and the concentration profiles within the interdiffusion zones can be directly detected by electron microprobe analysis.     

Die Prüfung von Halbzeug aus Kupferwerkstoffen auf Beständigkeit gegenüber Spannungsrißkorrosion

Testing of copper and copper-alloy semis for resistance to stress corrosion The mercurous nitrate test currently used to test the resistance to stress corrosion of copper and copper alloys is problematic. The testing agent is toxic and, moreover, it is not encountered as a corrosive agent. For these materials, the main source of corrosion is ammonia and its compounds. Therefore, a test on this basis is proposed, capable of replacing the mercurous nitrate test for the purposes of quality assurance, as experience has shown for about a year.