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.     

Untersuchung über das Korrosionsverhalten von Zirkoniumlegierungen. IV. Das Lochfraßverhalten Zirkoniumlegierungen

Investigation into corrosion behaviour of zirconium alloys. IV-Pitting behaviour of zirconium alloys Electrochemical investigations into the resistance of a number of Zr-alloys in different solutions against pitting corrosion have shown that additions of Va- and VIa-group metals and in particular Ti improve the resistance of pure Zr. Metals forming local elements decrease pitting corrosion resistance. Minor amounts of Fe, Ni and Cr have practically no influence. The pitting corrosion resistance of Zr and its alloys decreases with increasing concentration of chloride ions in the solutions. Additions of SO₄-ions retard the beginning of the pitting but do not shift the pitting corrosion potential. NO₃-ions on the other hand produce a real inhibition. Newly developed methods for the quick determination of the pitting corrosion potential were very useful for the described investigations.     

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.     

Neuentwicklung von Bleilegierungen aufgrund elektrochemischer Untersuchungen über das Korrosionsverhalten in Schwefelsäure

Development of new lead alloys starting from electrochemical investigations into the corrosion behaviour in sulfuric acid The corrosion of lead in sulfuric acid can take place in two different forms, corresponding to the active and passive state respectively of lead, but allowing for any intermediate stage as well. A surface layer is formed on principle, but it has different structure and effect in the two instances and requires a certain minimum duration of corrosion. Corrosion susceptibility can be substantially reduced, in particular by addition of low solubility in lead and which may thus give rise, as precipitates, to cathodic activity. Cu e.g. has a favorable effect which can be further improved by Sn. The same is true with noble metals – in particular Pd – having high hydrogen overtension. Complex alloys as e.g. PbCuPd yield a further increase in corrosion resistance and simultaneously, mechanical strength; an alloy of the type PbCuSnPd is superior to any other lead alloys as to corrosion and creep resistance.     

Untersuchungen über den Einfluß des Zinks auf das Korrosionsverhalten von Spannstählen

Investigations on the influence of zinc on the corrosion behavior of high strength steels Corrosion and fracture behavior of hot dip galvanized high strength steels with and without damaging zinc layer was studied in deionized water, in tap water, and in saturated calcium hydroxide solution through which nitrogen, air, and carbon dioxide were bubbled separately. Hydrogen permeation measurements have been carried out for steel specimens which were cathodically polarized by means of the zinc layer. It has been observed that the hydrogen activity reached to a maximum of 1-2 in neutral solutions and 4-10 in saturated calcium hydroxide solution or in dilute acid solutions containing carbon dioxide, before decreasing to low values. The decrease of hydrogen activity is due to the formation of surface layers. Constant load tests by application of a load amounting to 100-110% yield strength caused no hydrogen induced brittle fracture within 300-400 h neither with nor without damaging zinc layer. At a constant strain rate of 5· 10^?7/s only 8 mm cold drawn steel wires were found to be almost unsusceptible to hydrogen that was absorbed during the test. Under notched conditions, all the steels investigated showed macroscopic brittle fracture.     

Neuentwicklung von Bleilegierungen aufgrund elektrochemischer Untersuchungen über das Korrosionsverhalten in Schwefelsäure

Development of new lead alloys starting from electrochemical investigations into the corrosion behaviour in sulfuric acid The corrosion of lead in sulfuric acid can take place in two different forms, corresponding to the active and passive state respectively of lead, but allowing for any intermediate stage as well. A surface layer is formed on principle, but it has different structure and effect in the two instances and requires a certain minimum duration of corrosion. Corrosion susceptibility can be substantially reduced, in particular by addition of low solubility in lead and which may thus give rise, as precipitates, to cathodic activity. Cu e.g. has a favorable effect which can be further improved by Sn. The same is true with noble metals — in particular Pd — having high hydrogen overtension. Complex alloys as e.g. PbCuPd yield a further increase in corrosion resistance and, simultaneously, mechanical strength; an alloy of the type PbCuSnPd is superior to any other lead alloy as to corrosion and creep resistance.     

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.     

Neuere Untersuchungen über das Korrosionsverhalten und Korrosionsschutzmaßnahmen von Leichtmetall-Legierungen im Schiffbau und ähnlichen Anwendungsgebieten

Recent investigations into the corrosion behaviour and corrosion protection of light metal alloys in shipbuilding and similar applications The corrosion of Al and its alloys in seawater is due to the high anion defect concentration in the (natural or artificial) oxide skin; this structure facilitates anion adsorption (in particular adsorption of the small chloride ions), so that Al atoms are dissolved from the crystal and pitting corrosion may appear. This danger can be eliminated by Zn coatings on Al or by coupling Al with galvanized steel. This measure results in a certain anodic protection and an enforced general uniform corrosion. Flame-sprayed Zn coatings turn out to be most efficient while Cd coatings are clearly inferior. On the basis of experience gained with the stell/Al couple important variables affecting the corrosion behaviour are potential difference and current density (area ratio) and, in addition, the formation of electrolyte bridges. It is therefore important to prevent the formation of such bridges by careful sealing; it is necessary, however, to take account of the ageing behaviour of the particular sealant.     

Untersuchungen über das Korrosionsverhalten einiger Aluminiumlegierungen in strömendem Wasser bei 240° C

Investigation into the corrosion behaviour of some aluminium alloys in flowing water at 240° C The oxidation rate of certain aluminium alloys in flowing water (3.1 and 3.15 m/sec) has been studied under the following condition: 240°C, 39 kp/cm², PH 5–6. The most suitable âlloy was to be included in an investigation of potential sheathing materials for water-cooled nuclear reactors. The material tested included 5 alloys, one Al,1Ni, 0,5% Fe alloys, one Al, 1% Ni, 0,5% Fe alloy type X 8001 (2 modifications), one Al, 1% Ni, 0.3% Fe, 8–9% Si, and with 0.9% Mg respectively. The corrosion resistance was calculated on the basis of the metal losses determined after electrolytic dissolution of the oxide layer in boric acid. The corrosion rates were 0.03–0.05 mm/year with the alloy Al, 1% Ni, 9.5% Si (the specimens had been pre-oxidized), and 0.07–0.095 mm/year with the two Norwegian AlSi alloys. The highest rates were found with the two modifications of the American type: 0.09–0.13 mm/year and 0.13–0.30 mm/year respectively. Pre-oxidizing (pre-filming) at 240° C reduced the corrsion rates. There has been satisfactory general agreement between the results obtained and the data reported in available literature.     

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.     

Über das Korrosionsverhalten von Zink und feuerverzinktem Stahl in erwärmtem Wasser

Corrosion behaviour of zinc and hot dip galvanized steel in warm water The corrosion rate of zinc and hot dip galvanized steel in continuously flowing tap water is but little influenced by water temperature. The slight decrease of the corrosion rate which has been found at higher temperatures (60°C) can be attributed to the preferential formation of zinc oxide at these temperatures, this oxide being less soluble than the hydroxide formed at lower temperatures. The potential shift toward more noble values at higher temperatures does, however, depend from water composition and may eventually start as early as at 35 °C; in certain critical potential ranges the uniform corrosion may even be changed into pitting. Addition of phosphate to the water may reduce either the corrosion rate or it may restrict the potential shift (in this latter case the appearance pitting is prevented). The measurement of the electrode potential (not of the polarization resistance) thus yields information on the danger of pitting corrosion. The quality of the zinc surface seems to be important in those cases where the ZnFe alloy layer protrudes to the zinc surface.     

Über die Auswirkung von Seigerungen auf das Korrosionsverhalten austenitischer Cr-Ni-Mo-Stähle

Contribution to the Effect of Segregation on the Corrosion Resistance of Austenitic Cr-Ni-Mo-Steels Investigations of segregated austenitic Cr-Ni-Mo-steels by means of the Huey-test showed that even a short annealing at 800°C can reduce the corrosion resistance. Especially for steels having a pronounced segregation this reduction of corrosion resistance can be such that it hinders the practical application of the material. This sensitivity to corrosion can be explained by the formation of intermetallic phases from ferrite which appears in small quantities within the segregated areas. It can be reduced by slightly altering the chemical composition towards a better austenite-stability and by remelting the steels to lower their segregated.     

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.     

Einfluß von Seigerungen auf das Korrosionsverhalten von austenitischem nichtrostendem Schweißgut

Influence of segregations on the corrosion behaviour of austenitic stainless weld metal Fully austenitic stainless weld metal on solidification acquires a segregation structure. The segregation takes place with the participation of the alloying elements responsible for the corrosion behaviour. Regions of low alloy content are preferentially attacked and microelements form between them and more corrosion resistant regions. The progress of corrosion is enhanced by lamellar segregation structures and is inhibited by cellular structures. The corrosion due to segregations is particularly pronounced when the resistance in one medium is a pronounced function of an alloying element prone to segregation. This is demonstrated on the example of weld metal X 2 CrNiSi 1815 having different Si contents. The effect of the base metal/weld metal macro-element is discussed. Corrosion due to segregation takes place only when the weld metal is subject to attack in the vicinity of its resistance limit.     

Untersuchungen über Korrosionsvorgänge an Stahl nach einmaliger Chlorid-Kontamination

Investigations into the corrosion processes on steel after one-time's chloride contamination Investigation of chloride adsorption and desorption on mild steel St 37 (1.0120) and austenitic stainless steel X 5 CrNi 189 (1.4301) showed chloride adsorption layer, determined radiochemically, depends upon the material, the state of metal surface layer, and its pretreatment. Ground surface of St 37 retains comparatively less chloride ions on washing than an unpretreated specimen. On the other hand the chloride could be removed from the austenitic steel by rinsing twice in unagitated washing medium which lowered the chloride content to below the detection level of 0,02 m?g Cl^?/cm². Corrosion behaviour of specimens of 1.4301 in autoclave showed no difference with regards to corrosion in the test cycles of 300 and 400 h at 150 and 200° C whether or not the specimens were contaminated by chloride. Mild steels whose state of surface is similar to St 37 should be guarded against chloride contamination to prevent delayed damage. In case of steel similar to 1.4301 with regards to their surface characteristics cleaning the surface is relatively easy. Long time tests to assess risks of delayed damage are in progress and will be communicated later.     

Betrachtungen über das Eisen als mehrfache Mischelektrode

Iron—considered to be a multiple mixed electrode The system iron/aqueous solution is represented as a multiple mixed electrode with the cathodic potential-dependent electrode reactions The representation is made in a U_H (J_α, J_β, J) Diagram which turns out to be suitable for graphically representing the possible reactions of an iron electrode in the selected system. It is shown that only a limited number of these system can function as mixed electrodes.     

Der Einfluß von Martensit auf das Korrosionsverhalten von 18 Cr-10 Ni-Stahl

The effect of martensite on the corrosion properties of 18 Cr-10 Ni steel The corrosion properties of the martensitic phases formed in an austenitic matrix by (i) cooling to low temperature (-196 and ?269°C resp. ?320 and ?452°F) and (ii) cold working at room temperature was investigated for two chromium-nickel stainless steels of the 18 Cr10 Ni type. Austenite and martensite have the same chemical composition but different lattice structures. In sulfuric acid, both martensitic phases formed at low temperature and by cold working arc preferentially attacked in the active range of corrosion. The effect of potential on the corrosion attack was elucidated by potentiostatically controlled experiments with subsequent light-optical and SEM-investigation of the specimens. Selective corrosion attack of the martensitic phase was found down to a potential being 0.8 V more negative than the cathodic limiting potential of the active corrosion range of a fully austenitic steel, irrespective of the way of the martensite transformation. The preferential attack of martensite may be explained by the supposition that the deposition of cathodically protecting layers possibly consisting of nickel is rendered more difficult at the martensitic surface areas. In sulfuric acid, no differences in the corrosion properties between austenite and martensite were found in the passive and transpassive range. In chloride containing aqueous solutions, the resistance to pitting is not effected by martensite formed at low temperature. From this it is concluded that also martensite formed by cold working does not effect the pitting resistance.     

Untersuchungen über das elektrolytisch-potentiostatische Ätzen von nichtrostenden Stählen in 10 n NaOH unter Anwendung eines Coulometers

Investigations into the electrolytic-potentiostatic etching of stainless steels in 10 n NaOH, using a coulometer Current density/potential characteristics can only provide qualitative indications concerning the phenomena encountered with potentiostatic etching in 10 n NaOH. The process is best carried out in the trans-passive zone. Identification is based, not on the selective dissolution of certain standard components, but on the interference colours which can be observed as a result of the formation of cover layers of different thickness. The charge density/time characteristics also permit quantitative indications of the different phases. Current density/time curves permit a clarification of the mechanism govering the formation of cover layers. A ferritic steel (28 pC Cr) and a NiCr alloy (45 pC Cr) were found to follow a cubic law of growth, whilst CrNi steel 18-8 is initially governed by an approximately logarithmic law, followed by a zone extending over several hours where the growth begins to follow a parabolic law.     

Der Einfluß unterschiedlicher Nitratgehalte auf das Korrosionsverhalten von verzinkten Stahlrohren

The influence of different nitrate contents of drinking water on the corrosion behaviour of galvanized steel pipes At the water works Biblis and Alsbach of Südhessische Gas und Wasser AG, Darmstadt, field tests were performed over a period of 2 1/2 years to describe the influence of different nitrate contents in drinking water and the corrosion behaviour of different qualities of galvanized steel pipes. The results obtained showed, that weight loss and corrosion rate measurements give no information on this subject. Optical inspection and flushing tests could prove, that selective corrosion occurred in the water with higher nitrate content. Galvannealed pipes showed local corrosion attack after a certain exposition time in water with higher nitrate content, depending on flow velocity. Air blown galvanized pipes and galvannealed pipes in water with higher nitrate content additionally produce „Zinkgeriesel”︁ during flushing. The selective corrosion attack also takes place to a very small extent in galvanized steel pipes, where quality is in accordance to the German Standard DIN 2444.     

Einfluß einer Eisenaufmischung auf das Korrosionsverhalten von NiCu30 Fe-Stahlplattierungen

The influence of iron pick-up on the corrosion properties of NiCu30Fe/steel clad materials The influence of iron pick-up on the corrosion properties of overlay and butt weldings of NiCu30Fe/steel cald materials was investigated by electrochemical tests in aerated artificial sea water (ASTM Standard D 1141-75) at 25, 50 und 80°C and by exposure to sea water in a sea water test rig on Helgoland. NiCu30Fe plates with defined Fe contents between 0% and 14% were used for comparison. On the Fe being distributed homogeneously, no negative influence of the iron on the pitting resistance was noted in aerated artifical sea water of 25°C up to an Fe content of 10%. The pitting resistance increases with rising temperature (50 and 80°C) and the Fe influence increases slightly. On exposure to sea water on Helgoland, the corrosion in the subtidal zone is mainly caused by marine growth resulting in the formation of shallow pits. In the tidal zone, Fe contents of more than 6.7% cause rust pittings at very low integral corrosion rates (≤0.002 mm/a). With integral Fe contents of between 0.5% and 3% in the final pass, the overlay welds have the same good corrosion resistance properties as commercial NiCu30Fe plate material. The compound butt welds exhibit slight pitting in the weld metal and the heat-affected zone which cannot be conclusively attributed to Fe pick-up but is rather due to the different free corrosion potentials of the NiCu30Mn(Ti) weld metal and the NiCu30Fe cladding material. In the tidal zone which is the preferential application of NiCu30Fe corrosion rates are less than 0.01 mm/a for all specimens welded by different welding methods. Iron contents of up to 8% which can be met by all welding methods when welded in two layers have no negative effect on the corrosion properties.