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.     

Salzschmelzkorrosion gerichtet erstarrter eutektischer CO-Cr-C-Basis Superlegierungen bei hohen Temperaturen

Corrosion of directionally solidified eutectic Co-Cr-C-Superalloys by molton salts at high temperatures The corrosion behaviour of various directionally solidified 73C-class eutectic alloys (Co-Cr₇C₃) and the conventionally cast nickel base alloy IN 738* were investigated using a eutectic sulphate melt (sodium, calcium, and magnesium with 2% sodium chloride). As these materials are designed for high temperature applications, tests were carried out at 900°, 1000°, and 1100°. The additions to 73C were nickel, aluminium, and manganese. Corrosion surface attack for 73C and IN 738 was found to be similar. The grain boundary formation of sulphides and oxides in IN 738 is shown up as a disadvantage when compared with 73C as 73C has no grain boundaries perpendicular to the surface. This could possibly be compensated by directionally solidifying IN 738. A 10% nickel addition to 73C was found to increase the corrosion resistance, a 2% aluminium addition showed a minor improvement, and a 4.7 or 10% manganese addition to 73C to influence the corrosion resistance considerably.     

Corrosion of hot-dip-galvanised steel and zinc alloy-coated steel in ammonia and ammonium chloride

There are many potential causes of corrosion in animal buildings. Animals exhale large quantities of moisture into the air creating high relative humidity in the building if the moisture is not properly vented. High humidity increases the potential for condensation. In addition, ammonia may be found in large quantities in animal buildings. Ammonia is released from manure and urine. In addition, ammonium chloride is used as a nitrogen source in fertilisers. In this study, the atmospheric corrosion of hot-dip-galvanised steel and zinc alloy-coated steel such as zinc–aluminium and zinc–aluminium–magnesium has been studied in atmospheres containing different levels of ammonia. Investigations have also been conducted at different levels of ammonium chloride. The results are discussed in view of the mechanisms of corrosion of zinc and zinc alloy-coated steel in ammonia and ammonium chloride-containing environments.     

Einfluß von Beschichtungen auf das Schwingungsrißkorrosionsverhalten des Chromstahls X20Cr13

Influence of coatings on the corrosion fatigue behaviour of 13% chromium steel The influence of coatings on the corrosion fatigue behaviour of 13% chromium steel has been studied. There have been selected different coating systems: Barrier coating (enamel), diffusion coatings, (aluminizing, chromizing) and anodic coating, (aluminium, zinc, tin, cadmium). The corrosion fatigue limits of coated with uncoated specimens in neutral NaCl-solution are compared. Salt-concentrations were 0,01 and 22% (? 0,38 M) NaCl at 80°C and 150°C. The tests were carried out with alternating tensions and a constant frequency of 50 Hz. Only the use of andic coatings improved the corrosion fatigue behaviour of the chromium steel.     

Die Beeinflussung des Schwingungsrißkorrosionsverhaltens des Stahles X 20 Cr 13 durch einen Molybdänzusatz in chloridhaltigen Medien

Influence on the fatigue corrosion behaviour of the steel X20Cr13 in chloride containing media by molybdenum additions The fatigue corrosion behaviour of a 13% Cr steel (used for turbine blades) has been studied in terms of its dependence on carbide shape and molybdenum additions in aqueous NaCl solutions of various concentrations at temperatures between room temperature and 200°C. Further tests in autoclaves were carried out in order to study the surface layers formed above 150°C without mechanical loads. Addition of 1% molybdenum yields a considerable increase of corrosion fatigue strength at room temperature, while there is no influence attributable to different shapes of graphite precipitations. At 150°C the corrosion fatigue strength is largely independent from sodium chloride concentration (0,1 to 27%); this means that very small quantities of sodium chloride are sufficient to produce heavy corrosion in wet steam at > 106 cycles. A range particularly suitable for such tests is the load range between ± 150 and ± 200 N/mm² at 150°C, because these conditions approach those encountered in practice. The passivating layers are very thin (interference phenomena). Considering the increase of corrosion resistance produced by 1% Mo it is expected that 2.5% Mo will produce a further improvement, in particular with regard to pitting corrosion since rupture generally starts at the pits.     

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.     

In situ synchrotron X-ray diffraction study of scale formation during CO2 corrosion of carbon steel in sodium and magnesium chloride solutions

In situ synchrotron X-ray diffraction was used to follow the formation of corrosion products on carbon steel in CO₂ saturated NaCl solution and mixed NaCl/magnesium chloride (MgCl₂) at 80 °C. Siderite (FeCO₃) was the only phase formed in NaCl solution, while Fe(OH)₂CO₃ was also detected when MgCl₂ was present. The proposed model is that siderite precipitation, occurring once the critical supersaturation was exceeded within a defined boundary layer, caused local acidification which accelerated the anodic dissolution of iron. The current fell once a complete surface scale was formed. It is suggested that MgCl₂ addition decreased the required critical supersaturation for precipitation.     

Correlations between microstructure and surface properties in a high nitrogen martensitic stainless steel

Nitrided and tempered AISI 410S stainless steel was tested under corrosion–erosion conditions and compared to conventional AISI 420 martensitic stainless steel. The corrosion–erosion resistance of the nitrided specimens was higher than that of the AISI 420 steel when tempered at 200 °C, but it decreased with tempering temperature in the range between 200 and 600 °C. The higher corrosion–erosion resistance of the high-nitrogen steel was credited to a more homogeneous distribution of chromium in martensite and a lower number of coarse second-phase particles, especially for tempering temperatures below 550 °C. The hexagonal ϵ-nitride was identified in specimens tempered at 200 °C, while finely distributed cubic CrN nitrides were observed in specimens tempered between 400 and 600 °C. Hexagonal Cr₂N nitrides were observed at 550 and 600 °C. These coarse, high-chromium precipitates were responsible for the drop in corrosion resistance of the nitrided specimens.     

Corrosion of carbon steel underneath a lead/potassium chloride salt mixture

High amounts of lead in waste/recycled wood fuel are known to be a contributing factor to the increased corrosion often related to this type of fuel. In combination with potassium, usually present in the fuel, low‐melting point salt mixtures between lead chloride (PbCl ₂) and potassium chloride (KCl) are expected to form. The purpose of this study is to investigate reactions in the mixed salt of PbCl ₂ and KCl and its interactions with carbon steel P265GH and its oxide. Laboratory exposures were performed in an isothermal tube furnace with a salt mixture of PbCl ₂/KCl (50/50 mol%) put on steel samples. The test duration was 24 hr at either 300°C or 340°C in an atmosphere of 100 ppm HCl and 20 vol% H ₂O in synthetic air. After exposure, the salt mixture consists of distinct areas of KCl and PbCl ₂ but also the compounds K ₂PbCl ₄ and KPb ₂Cl ₅. A general observation is that the oxide thickness increases with temperature and that areas with Pb/K‐mixed salt are frequently found in close connection to more corroded areas. Often the more lead‐rich phase KPb ₂Cl ₅ is located closest to the corrosion product indicating its importance for the corrosion.     

Influence of Step Annealing Temperature on the Microstructure and Pitting Corrosion Resistance of SDSS UNS S32760 Welds

In the present work, the influence of step annealing heat treatment on the microstructure and pitting corrosion resistance of super duplex stainless steel UNS S32760 welds have been investigated. The pitting corrosion resistance in chloride solution was evaluated by potentiostatic measurements. The results showed that step annealing treatments in the temperature ranging from 550 to 1000 °C resulted in a precipitation of sigma phase and Cr₂N along the ferrite/austenite and ferrite/ferrite boundaries. At this temperature range, the metastable pits mainly nucleated around the precipitates formed in the grain boundary and ferrite phase. Above 1050 °C, the microstructure contains only austenite and ferrite phases. At this condition, the critical pitting temperature of samples successfully arrived to the highest value obtained in this study.     

Vergleichende Untersuchungen des SwRK-Verhaltens verschiedener Dampfturbinenschaufelstähle

Comparative investigations into the corrosion fatigue behaviour of different steam-turbine-blade steels Corrosion fatigue tests in NaCl-solution in the temperature range from ambient temperature to 150°C revealed a decrease of the corrosion fatigue strength of the steels X20Cr13 with 1% resp. 2.5% Mo, X4CrNiMo 16 5 1 and X2CrNiMoN 22 5 with increasing temperature; a minimum of the corrosion fatigue strength is reached at 150°C. At temperatures of about 80°C it was found an optimum corrosion fatigue behaviour of the Mo-alloyed steel X20CrMo13 2.5 in comparison with the other investigated steels. It was observed that crack initiation of the ferritic, Mo-alloyed steel is caused by Cl-induced pitting, of the soft martensitic steel by oxide inclusions and of the duplex steel by non metallic, brittle inclusions and/or by grain boundarys of the ferritic/austenitic microstructure. Crack initiation caused by pre-deformation at slip bands was observed on the duplex steel. All materials investigated failed at elevated temperatures. At temperatures higher than 80°C an optimum corrosion fatigue behaviour was not found.     

Solubility of chloride in molten magnesium metal

The solubilities of chloride (Cl) in liquid magnesium (Mg) have been determined from the analysis of quenched samples of liquid Mg equilibrated with NaCl-MgCl₂ melts of different compositions at temperatures in the range 650–790 °C. As an example, the solubility of Cl in liquid Mg in contact with pure MgCl₂ at 735 °C was found to be approximately 18 ppm. The Cl solubility was found to be proportional to the square root of the MgCl₂ activity in the NaCl-MgCl₂ melt, indicating that MgCl₂ dissolved according to the reaction 0.5MgCl₂ + 0.5Mg(l) = MgCl (in Mg). The temperature dependency of the solubility also was measured. Thermodynamic values related to the dissolution of MgCl₂ in liquid Mg have been estimated.     

Effect of Zinc Chloride in Ash in Oxidation Kinetics of Ni-Based and Fe-Based Alloys

Corrosion by molten phases leads to severe corrosion of heat exchangers in waste-to-energy plants. In addition, the presence of heavy metal chlorides in ash deposit increases degradation at low temperature due to the formation of highly corrosive molten phases. In this study, two heat exchanger materials, a low alloy steel (16Mo3) and a nickel based alloy (Inconel 625) were exposed in air to three different synthetic ashes, with various chloride contents, including ZnCl₂ at isothermal temperatures of 450 and 650 °C in a muffle furnace. After the test, thickness and mass losses were evaluated on two separate samples, and metallographic cross sections of the specimens were characterized via SEM/EDX analyses. Both measurement results were in good agreement and showed that the corrosion observed on both materials was higher in the presence of zinc chloride in ash at 450 °C than in ashes without heavy metal chloride at 650 °C.     

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.     

Production of Annealed Cold-Sprayed 316L Stainless Steel Coatings for Biomedical Applications and Their in-vitro Corrosion Response

316L powders were successfully deposited onto Al5052 aluminium substrates by cold spray method. Annealing was treated on the coated samples at 250–1000°C temperatures under Ar atmosphere. The in vitro performances of the coatings have been compared with using electrochemical corrosion test technique in the simulated body fluid (SBF) at body temperature (37°C). A scanning electron microscope (SEM-EDS) and X-ray diffraction (XRD) have been used for microstructural characterization and phases identifications of the coatings, respectively. The results were shown that there are high adhesions at particle and substrate interfaces and between the particles deposited as well. Also, the increasing annealing temperature increases corrosion resistance of the cold sprayed 316L stainless steel coatings. The corrosion susceptibility of the coating annealed at 1000°C was similar that of standard 316L stainless steel implant material in Ringer’s solution. The microstructural observations revealed that corrosion starts between the inter-splat powders and continues throughout the surface not in-depth.     

Effect of small amounts of alloyed tin on the electrochemical behaviour of aluminium in sodium chloride solution

Binary model AlSn alloys containing 30–1000 ppm (by weight) Sn were investigated by electrochemical polarization in 5 wt% chloride solution and subsequent characterization of corrosion morphology. In the homogenized and rolled condition, tin concentration only slightly affected electrochemical behaviour up to 500 ppm, and the pitting potentials were all about −0.8 V_SCE. However, alloy containing 1000 ppm Sn was significantly activated by lowering of the passivity-breakdown potential to −1.38 V_SCE. Annealing at 300 °C caused significant segregation of Sn to the metal surface, and all specimens, independent of bulk Sn concentration, became nearly similarly active with breakdown potentials around −1.2 V_SCE. Corrosion on 300 °C-annealed specimens was uniformly distributed by polarization below the bulk pitting potential of −0.76 V_SCE. Moreover, the activation effect was temporary, and corrosion was significantly reduced as the segregated Sn was etched away from the surface. Thick oxide, formed during water quenching on high Sn concentration samples, containing 500 and 1000 ppm Sn, introduced partial passivation during polarization test. Annealing at 600 °C caused increasing activation with increasing Sn concentration, caused by Sn enrichment at the metal surface by dealloying of aluminium during anodic polarization in chloride solution. Corrosion was localized in the form of grain boundary corrosion for alloyed Sn concentration less than and equal to 500 ppm and pitting following the triple grain boundaries for 1000 ppm.     

Korrosion des Hastelloy C 4 und anderer metallischer Werkstoffe in heißen,konzentrierten Salzlaugen

Corrosion of Hastelloy C4 and different metallic materials in hot concentrated salt brines In a quaternary salt brine saturated at 55°C with magnesium chloride, potassium chloride and sodium chloride, polarization curves were measured in the temperature range from 100°C to 200°C at different materials in order to study their corrosion behaviour. Steels and nickel corrode in the active state. The corrosion current density of an unalloyed steel at 100°C was about 20 μA/cm² corresponding to a removal rate of 0.2 mm/a. Iron-silicon and nickel corrode significantly slower at a rate of a few μA/cm². Steady state corrosion rates of Hastelloy C 4 and of titanium at 100°C are 10 nA/cm² and less than 4.5 nA/cm², respectively. For both materials, the susceptibility to pitting grows with the temperature and with the chloride concentration. The steady state corrosion rates of passive Hastelloy C 4 depend on temperature according to an activation enthalpy of 85 kJ/mol and become about 5 μA/cm² at 200°C. Even at high temperatures steady states are attained rather slowly within about one day. The critical pitting potentials approach the corrosion potentials in deaerated solution at a rate of about 0.8 mV/K. At 200°C the critical pitting potential is only 90 mV positive to the corrosion potential. Thus, Hastelloy C 4 may be used at high temperatures, only if it is cathodically protected.     

腐蚀产物MgO对Fe基合金在固态和熔融NaCl-MgCl2 中高温耐蚀性能的影响

熔融氯化盐是下一代聚光式太阳能热发电站（第3代CSP）候选传热和储热介质,含MgCl₂的熔融氯化盐对金属传热管道和储热容器腐蚀后在其表面形成MgO,MgO对管道耐腐蚀性能影响尚不清楚。通过对比碳钢和3种Fe-Cr-Ni合金在固态（345 ℃）和熔融NaCl-MgCl₂（445和545 ℃）中的腐蚀行为,分析了MgO对4种试样在不同温度下的腐蚀行为机理。结果表明,在固态NaCl-MgCl₂中,碳钢表面MgO壳致密且连续,可以保护试样免受腐蚀。在熔融NaCl-MgCl₂中,4种试样表面也生成了致密的MgO壳,但它因热应力作用而开裂和剥落,熔融盐沿着氧化膜裂纹渗入MgO/基体界面,发生化学-电化学联合腐蚀反应,不能保护试样免受该熔盐腐蚀。     

Laboratory investigation on the condensation and corrosion rates of top of line corrosion in carbon steel: a case study from pipeline transporting wet gas in elevated temperature

A glass cell was designed to simulate the condition for top of line corrosion encountered in wet gas transportation pipelines. Aqueous solution of 3 wt-% NaCl saturated with CO₂ at atmospheric pressure was employed. Effect of temperature gradient in the formation of condensation and its rate was investigated. API 5L Grade X65 carbon steel material was used as the working electrode for the experiment. The condensation rate was measured for the temperature gradient of 20°C, 30°C and 50°C under atmospheric condition for 24?h duration of the experiment. The corrosion rate of the specimens was measured using weight loss and Linear Polarisation Resistance (LPR) techniques. The LPR probe was immersed in the collected condensed water from the experiment to calculate the corrosion rate. The measured corrosion rate from the weight loss technique was in agreement with the corrosion rate measured from LPR. The corrosion rate measurement was repeated with the addition of 1000?ppm of pH modifying agent. This study indicates that the corrosion rate of pipeline and piping when subject to temperature gradient of 50°C and above is very high and alarming.     

Thermogravimetric Study of Oxidation-Resistant Alloys for High-Temperature Solar Receivers

Three special alloys likely to be suitable for high-temperature solar receivers were studied for their resistance to oxidation up to a temperature of 1050°C in dry atmospheres of CO₂ and air. The alloys were Haynes HR160, Hastelloy X, and Haynes 230, all nickel-based alloys with greater than 20% chromium content. The oxidation rate of specimens cut from sample master alloys was followed by thermogravimetry by continuously monitoring the weight change with a microbalance for a test duration of 10 h. The corrosion resistance was deduced from the total weight increase of the specimens and the morphology of the oxide scale. The surface oxide layer formed (scale) was characterized by scanning electron microscopy and energy dispersive x-ray spectroscopy and in all cases was found to be chromia. Oxidation was analyzed by means of parabolic rate law, albeit in some instances linear breakaway corrosion was also observed. For the temperature range investigated, all alloys corroded more in CO₂ than in air due to the formation of a stronger and more protective oxide scale in the presence of air. At 1000°C, the most resistant alloy to corrosion in CO₂ was Haynes 230. Alloy Haynes HR160 was the most oxidized alloy at 1000°C in both CO₂ and air. Hastelloy X oxidized to a similar extent in CO₂ at both 900°C and 1000°C, but in air, it resisted oxidation better at 1000°C than either at 900°C or 1000°C.