The corrosion behaviour of nickel in hydrogen chloride gas and gas mixtures of hydrogen chloride and oxygen at high temperatures

A kinetic investigation of corrosion of nickel in hydrogen chloride gases containing 0–75% oxygen at 400–700°C was carried out by the thermogravimetric method. There was no great difference in the corrosion behaviour of nickel in the hydrogen chloride gas and its mixtures with oxygen because of exclusive formation of NiCl₂ scale, regardless of the gas compositions. The corrosion behaviour showed the mixed reaction mode; that is, NiCl₂ scale formation according to parabolic kinetics and NiCl₂ scale evaporation according to linear kinetics. With increasing temperature above 500°C, linear kinetics became predominant.     

The corrosion behaviour of chromium in hydrogen chloride gas and gas mixtures of hydrogen chloride and oxygen at high temperatures

A kinetic investigation of the CrHClO₂ system at 1 atm was carried out varying the oxygen content from 0 to 75 vol% at 400–800°C by the thermogravimetric method in stagnant gases and by measurements of weight loss and weight of sublimates after corrosion tests in flowing gases. In hydrogen chloride gas the corrosion rate is determined by the rates of formation and evaporation of a CrCl₂ scale: the scale was protective, to some extent, up to 600°C, but rapidly evaporated at still higher temperatures. The addition of oxygen led to suppression of corrosion loss up to about 500°C but to catastrophic corrosion at higher temperatures. The scale formed in the gas mixtures consisted mainly of Cr₂O₃ but vigorous vaporization of CrCl₂ and water occurred at the higher temperatures due to oxy-chlorination.     

High Temperature Corrosion of the Alloy Ni4Mo in a hydrogen chloride atmosphere

Specimens of the alloy Ni₄Mo were tested in a hydrogen chloride atmosphere at temperatures between 400° – 850° C. The corrosion of the alloy was followed by gravimetric analyses and microstructural examinations. It was found that the layer formed on the specimens due to corrosion is adherent but porous, thus allowing the volatilization of some of the corrosion products. The formation of various kinds of oxides and chlorides was observed. The exact composition of the scale depended on the temperature of exposure to hydrogen chloride and on the amount of oxygen present as an impurity in the test apparatus. The formation of a domain structure in the uncorroded alloy affects the morphology of the scale/alloy interface.     

The effect of hydrogen chloride on the corrosion of an FeCrAlY alloy in simulated coal gasifier atmospheres

An iron chromium aluminium yttrium steel was exposed to a simulated coal gasifier atmosphere containing 1000 ppm and 2200 ppm hydrogen chloride at 450 °C. Increasing hydrogen chloride content was found to accelerate reaction rates, and significantly alter the microstructure and composition of the corrosion product. Tentative explanations for these results, involving vapour phase transport of metal chlorides are proposed.     

Hochtemperaturkorrosion von Nickel in Chlor und Chlor-Sauerstoffgemischen

High temperature corrosion of nickel in chlorine and chloride oxygen mixtures Investigation of the chlorination and oxychlorination of nickel in a quartz ap-paratus at 600 to 850°C. In chlorine a surface layer of Ni chloride is formed which adheres well to the metal surface up to 75O°C, while it is damaged by spalling at higher temperatures. The reaction rate depends from temperature, chlorine partial pressure and flow velocity. The kinetic law is parabolic but undergoes a pronounced change at higher temperatures because of the sublimation of nickel chloride. In chlorine-oxygen mixtures there may be processes similar to combustion at chlorine contents as low as about 1.2 Vol.-%. This fact can be attributed to the hinderance by oxy-gen of the normally occurring dissociation of NiCl; this reaction is substituted by another one yielding on the one hand NiO, on the other hand chlorine.     

Sequence of steps in the pitting of aluminum by chloride ions

Corrosion pit initiation in chloride solutions is given by an electrode kinetic model which takes into account adsorption of chloride ions on the oxide surface, penetration of chloride ions through the oxide film, and localized dissolution of aluminum at the metal/oxide interface in consecutive one-electron transfer reactions. A previous model has been extended here to consider that penetration of chloride ions can occur by oxide film dissolution as well as by migration through oxygen vacancies. Pit initiation occurs by chloride-assisted localized dissolution at the oxide/metal interface. The electrode kinetic model leads to a mathematical expression which shows that the critical pitting potential is a linear function of the logarithm of the chloride concentration (at constant pH), in agreement with experiment. The model also predicts that the critical pitting potential is independent of pH (at constant chloride concentration), also in agreement with experiment. Corrosion pit propagation leads to formation of blisters beneath the oxide film due to localized reactions which produce an acidic localized environment. The blisters subsequently rupture due to the formation of hydrogen gas in the occluded corrosion cell. Calculation of the local pH within a blister from the calculated hydrogen pressure within the blister gives pH values in the range 0.85 to 2.3.     

Corrosion of iron–aluminium alloys in gaseous atmosphere containing hydrogen chloride and hydrogen sulphide at 600 and 700°C

Abstract

The corrosion of two binary iron–aluminium alloys was compared in gaseous CO₂–H₂–HCl–H₂S and CO₂–H₂ mixtures at 600 and 700°C. In each environment, the Fe–14Al alloy resisted corrosion due to the formation of a protective alumina scale. The Fe–4Al alloy corroded more rapidly in the CO₂–H₂–HCl–H₂S atmosphere than in the CO₂–H₂ atmosphere at both temperatures. The corrosion products comprised thick outer layers of iron oxide, porous inner layers of mixed iron–aluminium oxide and internal precipitates of aluminium oxide. Sulphur was detected near the scale/alloy interface and the increase in corrosion rate was attributed to the presence of chlorine and sulphur.     

Stress corrosion cracking of Inconel 600 in aqueous solutions at elevated temperature Part II: Effects of chloride and sulphate ions on the electrochemical behaviour of Inconel 600

The influencing effects of temperature, potential and electrolyte composition on the electrochemical behaviour of Inconel 600 in aqueous solutions are presented. Considering these effects the connection between the data have been obtained from chemo-mechanical fracture investigation on CT-samples in Part I of this paper and pitting corrosion are discussed. The results have shown that chloride ions depassivate the surfaces of cracks locally and hinder the formation of a new protective oxide layer on the fracture surfaces. Furthermore, chloride promotes the dissolution of metal and initiates the cracking, respectively. The resulting crevice corrosion promotes an increase of hydrogen absorption by the metal. The increase of the hydrogen content of the metal influences the mechanical fracture behaviour. Contrary, sulphateions inhibit the initiation of corrosion mainly due to a hinderance of chloride ions adsorption on active sites of the fracture surfaces. The initiation of localized corrosion in the crevice region may be stimulated by chromate ions formed by oxidation of chromium from the oxide layer or the base metal in oxygen containing solutions.     

The enrichment of hydrogen and chloride ions in the crevice corrosion of steels

The changes in concentration of hydrogen and chloride ions during corrosion in an artificial crevice on steel were observed from potential changes of Pd-H and Ag/AgCl micro-electrodes inserted in the crevice. Increasing the bulk chloride ion concentration accelerated the rate of pH change and resulted in more acidic conditions in the crevice. Such pH changes were delayed by the addition of inhibitor such as dialkylamines. Though the free chloride ion concentration did not change appreciably, the total concentration of free and complex ions in the crevice increased with continuous dissolution of the steel. Increasing the hydrogen and total chloride ion concentration in the crevice accelerated the anodic dissolution of steels within the crevice.     

The corrosion of pure niobium in oxidizing,sulfidizing, and oxidizing-sulfidizing gas mixtures at 600–800°C

The corrosion of pure niobium has been studied at 600–800°C in various environments as part of a study of the corrosion resistance of its alloys with iron, cobalt, and nickel to atmospheres of low-oxygen and/or high-sulfur activities. The results have shown that not only the sulfidation but also the corrosion in mixed atmospheres and particularly the oxidation under low oxygen pressures of pure niobium are quite slow, with kinetics rather similar in the three types of gas mixtures used. The good corrosion resistance of niobium to attack by oxygen under low pressures is quite interesting because this element is corroded very rapidly by oxygen under high oxygen pressures, due to the formation of the nonprotective highest oxide Nb₂O₅ as a main corrosion product.     

Influence of gas phase composition on the kinetics of chloride melt induced corrosion of pure iron (EU‐project OPTICORR)

Heat exchanger tubes in waste‐fired boilers are usually attacked by aggressive gases like oxygen, HCl and water vapour as well as by solid and molten salts. Especially if the salt deposit is molten, these compounds cause acceleration of the corrosion process. This study focuses on kinetic investigations on the influence of gas phase composition (O₂, HCl and H₂O) on the chloride melt induced corrosion of Fe. Thermogravimetric (TG) tests were conducted on Fe covered by a 50 mol.% KCl/50 mol.% ZnCl₂‐salt mixture at T = 320°C, first in an Ar ‐ O₂ ‐ atmosphere. In these experiments the amounts of salt deposit (15 and 30 mg/cm²) and oxygen (4–16 vol.%) were varied to investigate their influences on corrosion kinetics. The TG curves show three kinetic stages, i.e. an incubation phase, a linear stage and a logarithmic/parabolic stage [1]. Further it could be shown that the duration of the incubation phase and the slope of the linear stage depend on the amount of the salt deposit as well as on the oxygen partial pressure (p(O₂)). The incubation time increases with increasing amount of salt deposit and decreases with increasing p(O₂). Experiments that were carried out in an Ar – O₂ – HCl atmosphere (500–2000 vppm HCl, 4–16 vol.% O₂) yield enhanced mass gain in comparison to TG tests without HCl. In atmospheres containing at least 1000 vppm HCl corrosion starts immediately without going through an incubation phase following a linear rate law. In the next stage the TG curve follows a rate law that is either parabolic or logarithmic. At higher amounts of HCl (2000 vppm, 8 vol.% O₂) the TG curve shows a relative mass loss after about 55 h of corrosion indicating an evaporation of iron chloride. This phenomenon was also observed at 1000 vppm HCl and 16 vol.% O₂ but not in the other experiments presented in this study. Experiments carried out in Ar – O₂ – H₂O are discussed also. In general the TG curves show lower mass gains after some hours of corrosion in comparison to TG tests without H₂O but at the beginning a shortened incubation phase is evident.     

The chloride corrosion of austenitic stainless steels and of an inconel alloy in hot acidic media

Open circuit corrosion testing of austenitic stainless steels, AISI types 304, 310 and 316, and of an Inconel alloy in boiling 5% NaCl solution at pH 2.5 was carried out. The influences of aeration and the introduction of Cl₂ and/or H₂S were also examined. Cl₂ accelerated corrosion, pitting and crack formation whereas H₂S had an inhibiting effect on the corrosion rates and pitting but induced hydrogen attack, which appeared in the form of blisters on the surface specimen. H₂S in the absence of oxygen resulted in the growth of corrosion product on the specimen surface, instead of dissolution, but the cracking tendency also increased due to hydrogen penetration. Addition of trisodium phosphate to the corrosive solution markedly reduced pitting and lowered the corrosion rate by approximately half. Throughout the various tests it was found that the resistance of different alloys to hot chloride corrosion was in the order 310 > 316 > 304 > Inconel.     

Water corrosion studies of AlMg (5154) and AlCuMg (2024) aluminium alloys by gas chromatography

An original method, based on gas chromatography, is used to study the water corrosion of 5154 and 2024 foils. Measurements of volumes of hydrogen evolved by the attack of distilled water on the alloys, subject to a temperature of 70°C in a variable frequency oscillating oven, reveal the importance of erosion-abrasion factors in the corrosion reaction kinetics. This study shows that the presence of oxygen is not significantly involved in the corrosion of 5154 foils, and a corrosion mechanism for this alloy is proposed. Under similar erosion-abrasion conditions, the corrosion rates of the 38 μm 2024 foils are closely comparable to those observed with 28 μm 5154 foils. The reactions stemming from the attack, however, cause the evolution of hydrogen to be accompanied by oxygen absorption. Thus an important factor in the corrosion of 2024 foils is displayed: environment aeration. The corrosion mechanisms of the 2024 rolled foils involves cathodic reactions, with or without hydrogen evolution, leading to the formation of hydroxides. This preliminary study shows that the honeycomb composite structures (i.e. NIDA), widely used in the aircraft industry, can come under strong attack from the water corrosion if they are used without protective coating or if the coating is damaged.     

The anoxic corrosion behaviour of copper in the presence of chloride and sulphide

The Canadian used fuel container for the long-term containment of spent nuclear fuel in a deep geological repository comprises a 3-mm copper corrosion barrier applied directly to a strong carbon steel container. Although a final site for the Canadian deep geological repository has not yet been chosen, the site selection process has narrowed down to two candidate locations with unique groundwater chemistry, particularly with respect to salinity. Therefore, to ensure the long-term integrity of the used fuel container, the effect of a range of groundwater chemistries on copper corrosion must be understood. The primary variables of interest are the influence of chloride concentration and the consequences of the interaction of hydrogen sulphide, naturally present in the groundwaters in very low concentrations, with the copper cladding. An additional aspect that has been investigated is the behaviour of copper in pure water. The anoxic corrosion of copper can be inferred by the very slow release of hydrogen gas. In this paper, new data are presented, which demonstrate an extremely sensitive approach to quantify the very limited hydrogen release at 75°C. Initially, corrosion rates under conditions approximating an anticipated Canadian deep geological repository were significantly less than 0.5 nm/year and they invariably declined over the course of several months/years. The presence of chloride or hydrogen sulphide was found, under specific conditions, to stimulate short-term corrosion behaviour, which was consistent with anion-assisted surface rearrangement, not bulk corrosion.     

Effect of hydrogen sulphide on The corrosion behaviour of titanium

In this paper the effect of hydrogen sulphide on the electrochemical and corrosion behaviour of VT 1–0 commercial titanium has been studied in acidic solutions containing polarization and analytical methods. Neither in the presence of sulphate nor chloride ions hydrogen sulphide affected electrochemical corrosion parameters in less acidic solutions but in 1 M sulphuric and hydrochloric acid where the increase of the corrosion rate can be attributed first of all to the decrease of the hydrogen overvoltage. The interpretation of the results is based on considerations including the role of titanium hydrides formed during the processes.     

The contribution of hydrogen to the corrosion of 2024 aluminium alloy exposed to thermal and environmental cycling in chloride media

This work is focused on the role of hydrogen in corrosion damage induced by the cyclic exposure of 2024 aluminium alloy to chloride media with air emersion periods at room and/or negative temperatures. Various analysis and microscopic observation techniques were applied at intergranular corrosion defects. A mechanism involving the contribution of hydrogen to the degradation of the alloy mechanical properties is presented. Several consecutive stress states appear during cycling, resulting from volume expansion of the electrolyte trapped in the intergranular defects during emersion phases at −20 °C. These stress states lead to hydrogen diffusion, transport and trapping.     

Das Korrosionsverhalten von Eisen,Zink, Aluminium und Chromnickelstahl im System Methanol-Wasser-Chlorwasserstoff

Corrosion behaviour of iron, zinc, aluminium and chromium nickel steel in the system methanol/water/hydrogen chloride The influence of water on the corrosion behaviour of pure iron, zinc, aluminium and normal 18 9 CrNi steel in hydrogen chloride containing methanol has been studied. The immersion tests and the tracing of potential dynamic current density potential curves were carried out at 20°C, oxygen being excluded. Even small quantities of water may give rise to a considerable decrease of corrosion rates. This effect is attributed in the case of iron, zinc and chromium nickel steel to increased hydrogen overvoltage, which exhibits a sudden jump between 0 and 15 Vol.-% water. Heterogenous cathodic limiting reaction currents are observed on iron. In the case of aluminium the change in corrosion rates toward lower values is caused by the inhibited anodic partial reaction. Addition of 5 Vol.-% water gives rise to a displacement of the pitting potential by approx. 400 mV in the positive direction, accompanied by a decreasing corrosion rate by about three orders. Anodic polarization of chromium nickel steel reveals that this steel can be passivated only beyond a critical water content of approx. 50 Vol.-%. A further increase of the water content gives rise to a sudden decrease of the critical passivation current density and the passivity current density. Simultaneously, the passivation potential moves toward more negative values.     

Characterisation and comparison of corrosion products originated in steel pipelines transporting sour gas and crude oil

In this work, X-ray diffraction and Mössbauer spectroscopy techniques were used to characterise and carry out a comparison of the corrosion products obtained during the pigging activities in two sour-hydrocarbon-transporting pipelines located in the Gulf of Mexico: the first one being a gas pipeline and the other one a crude oil pipeline. The results indicate that for these specific conditions, there are differences between the corrosion products formed in each pipeline. Iron sulphides and oxides were the main corrosion products and their presence is directly related to the operating conditions prevailing in the pipelines as well as to the hydrocarbon quality. As for the sour gas pipeline, higher concentrations of greigite and pyrite were observed, whereas more proportions of magnetite, mackinawite and marcasite were found in the sour crude oil pipeline. The most important parameters in the formation of the different types of corrosion products are the water content, hydrogen sulphide concentration and oxygen presence in the system.     

Corrosion of mild steel under heat transfer in high temperature aerated sodium chloride solutions

It is suggested that acidity may be generated at high temperatures by a mechanism analogous to the pitting/crevice corrosion which occurs at room temperature in oxygenated chloride solutions. The corrosion rate of mild steel was monitored in oxygenated and de-oxygenated 100 p.p.m. sodium chloride solutions at temperatures between 200° and 350°C at heat fluxes of 110–260 kW/m². Corrosion rates were measured by determining the hydrogen generated.In de-oxygenated solutions, corrosion rates were low and a thin magnetite film was found on both heated and unheated surfaces. In oxygenated solutions, severe corrosion occurred at heated surfaces forming a thick laminated oxide scale.     

On the use of mercury-coated tips in scanning electrochemical microscopy to investigate galvanic corrosion processes involving zinc and iron

The corrosion processes related to zinc dissolution that take place in an iron–zinc galvanic pair exposed to a chloride solution were investigated by scanning electrochemical microscopy (SECM) using a mercury-coated platinum microelectrode as SECM tip. Both the release of zinc ions and the consumption of dissolved oxygen that occur in separate sites at the iron–zinc galvanic pair were monitored. Zinc ion quantification could be performed by stripping the zinc metal collected at the Hg-coated tip using linear sweep voltammetry.