Chlorine-induced High-temperature Corrosion Research Articles

Chlorine-induced high-temperature corrosion of the Pt-modified aluminide coating in simulated marine environment

The corrosion behavior of a single phase Pt-modified aluminide coating in the marine environment was investigated through a novel cyclically alternate corrosion test. The results showed that the multilayer oxide scale with loose structure was formed on the coating. NaCl and water vapor were verified to play important roles in enhancing the aggressivity during the corrosion test, in which the presence of NaCl increased cracking and spallation tendency of the oxide scale, and the addition of water vapor accelerated the oxidation rate and promoted internal oxidation to the coating.

Chlorine-induced high-temperature corrosion characteristics of Ni-Cr alloy cladding layer and Ni-Cr-Mo alloy cladding layer

The thickness loss rate was applied to evaluate the chlorine-induced high-temperature corrosion properties of four nickel-based cladding layers. The results indicate that merely increasing the Cr content cannot improve the corrosion resistance, but instead severely aggravates the internal corrosion. The characteristics of laser cladding technology render the role of Mo in enhancing corrosion resistance closely related to its content and distribution. Transverse penetration cracks tend to occur in NiO surrounded by NiCr2O4. However, the generation of short rod-like NbO2 enhances the mechanical properties of the NiO layer, leading to the absence of such cracks.

Influence of water vapor on the chlorine-induced high-temperature corrosion behavior of nickel aluminide coatings

Nickel aluminide coatings were prepared by aluminizing pure nickel at 700 ℃ for 6 h. The corrosion behavior of nickel aluminide coatings was investigated under a KCl deposit environment (95 %N2 +5%O2) alone or with 15 % or 30 % water vapor at 700℃. Without water vapor, the coatings suffered slight surface and intergranular corrosion attack. With water vapor increasing to 30 %, the generation of chlorine is inhabited and reduces the “chlorine-active corrosion”. However, with 30 % water vapor, the oxidation-decomposition reaction becomes more active, so more corrosion products accumulate on the surface and the degradation of coatings was more severe.

Chlorine-Induced High Temperature Corrosion of Inconel 625 Alloy with the Addition of Yttrium at 800 °C

Chlorine-Induced High Temperature Corrosion of Inconel 625 Alloy with the Addition of Yttrium at 800 °C

Effect of Hydrogen Chloride on Corrosion Behaviour of Fe–Cr Alloys in Wet CO2 Gas at 650 °C

Chlorine-induced high-temperature corrosion is a major problem for structural materials used in incinerators because of the release of hydrochloride during waste combustion. In this work, the effect of HCl additions (0.05 and 0.1 vol%) to a N2–10CO2–10H2O gas on the oxidation of binary ferritic Fe—(15, 20, 25 and 30 wt%) Cr alloys was investigated at 650 °C. The addition of HCl significantly increased the rate of weight gain during reaction. Thick multi-layered iron-rich oxide scales formed on Fe-15Cr in all gases. Increasing Cr content increased the tendency for Cr2O3 scale formation, leading to complete protection for Fe-25Cr in HCl-free gas, but a level of 30Cr was required in the presence of HCl. Mechanisms underlying the effect of chlorine on the critical Cr concentration required for protective chromia formation are explored.

Two-step numerical procedure on the removal process of gaseous potassium chloride generated from waste incineration via the injection of sulfate-based additives

Gaseous potassium chloride (KCl) that constitutes a relatively large portion of the combustion gas of municipal solid waste can condense on the surface of boiler heat exchanger tubes, causing severe corrosion attacks. To reduce the chlorine-induced high-temperature corrosion, sulfate-based additives have been used. In this study, a two-step numerical procedure is proposed to quickly predict the effect of the injection of sulfate-based additives on the removal of gaseous KCl. A computational fluid dynamics (CFD) simulation is first carried out to obtain the temperature distribution. Then, the thermal decomposition of sulfate additives, sulfation of gaseous KCl, and condensation of K2SO4 are calculated to predict the species concentration profiles at the temperature conditions given by the CFD simulation. After validation with a laboratory-scale experiment using NH42SO4, the procedure is applied to a pilot-scale boiler to examine the effects of NH42SO4, Fe2SO43, and Al2SO43. The calculation results show that each additive has an optimal injection temperature range: approximately 800 °C for NH42SO4 and 1000 °C for both Fe2SO43 and Al2SO43, which are consistent with the values reported in the literature. The expressions for the stoichiometric KCl removal efficiency of each additive are derived and compared with the calculated efficiencies.

Chlorine-induced high-temperature corrosion and erosion-corrosion of HVAF and HVOF-sprayed amorphous Fe-based coatings

Chlorine-induced high-temperature corrosion and erosion-corrosion behavior of amorphous Fe-based coatings sprayed by high velocity air-fuel (HVAF) and high velocity oxy-fuel (HVOF) techniques were investigated. The coated specimens were first exposed to isothermal high-temperature corrosion at 600 °C in ambient air with and without KCl. The exposed specimens were then subjected to alumina erodent. The as-sprayed HVAF coating showed a more compact and uniform microstructure with a higher hardness leading to higher corrosion and erosion-corrosion resistance. After erosion, all the coatings similarly exhibited a combined brittle/ductile damage to surface oxide scale that previously formed in the corrosive environment. The corrosion and erosion-corrosion behavior of the coatings primarily relied on the uniformity of coatings' microstructure and distribution of alloying elements to form the protective oxide scale in the corrosive environment, which can resist against erodent in the erosive media.

Effect of SiO2 Dispersion on Chlorine-Induced High-Temperature Corrosion of High-Velocity Air-Fuel Sprayed NiCrMo Coating

NiCrMo coatings with and without dispersed SiO2 were deposited using high-velocity air-fuel technique. Thermogravimetric experiments were conducted in 5% O2 + 500 vppm HCl + N2 with and without a KCl deposit at 600°C for up to 168 h. The SiO2-containing coating showed lower weight change as a result of formation of a protective and adherent Cr-rich oxide scale. SiO2 decelerated short-circuit diffusion of Cr3+ through scale’s defects, e.g., vacancies, and promoted the selective oxidation of Cr to form the protective Cr-rich oxide scale. Furthermore, the presence of SiO2 led to less subsurface depletion of Cr in the coating, and accordingly less corrosion of the substrate. The formed corrosion product on the SiO2-free coating was highly porous, non-adherent, and thick.

Chlorine-Induced High-Temperature Corrosion of Boiler Steels Combusting Sha Erhu Coal Compared to Biomass

Chlorine, as the harmful element with high volatility and reactivity existing in certain coal and biofuels, mainly contributes to severe deposit formation and high-temperature corrosion. Sha Erhu (SEH) coal is characterized with high amounts of alkali metal (mainly sodium, Na) and chlorine (Cl) and relatively smaller amounts of sulfur (S), which is close to the characteristics of biomass. However, the proportion of ash and mineral in most biomass is far lower than that in coal, while the volatile and potassium (K) content is typically higher. In light of these distinct corrosive elements, comparative investigation of the high-temperature corrosion characteristics of boiler steels (T91, 12Cr1MoVG, and TP347H) firing high- or low-chlorine coal and biomass is meaningful. A series of 168 h corrosion experiments involving SEH ash, Da Nahu (DNH) ash, straw ash, wood chip ash, and their mixtures were performed on the tube furnace with the designing a new type of double-tube corrosion probe to consider temperatur...

Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings

Chlorine-induced corrosion of HVAF-sprayed Ni21Cr and Ni5Al coatings was investigated in 5 vol.% O2 + 500vppm HCl + N2 with and without KCl at 600 °C up to 168 h. Both coatings were protective in the absence of KCl. With KCl, Ni21Cr degraded through a two-stage mechanism: 1) formation of K2CrO4 followed by diffusion of Cl− through the oxide grain boundaries to yield chlorine and a non-protective oxide, and 2) inward diffusion of chlorine though defects in the non-protective oxide, leading to breakaway oxidation. Cl−/Cl2 could not diffuse through the protective alumina scale formed on Ni5Al, hence the corrosion resistance increased.

Effect of Carbide Dissolution on Chlorine Induced High Temperature Corrosion of HVOF and HVAF Sprayed Cr3C2-NiCrMoNb Coatings

Highly corrosion- and wear-resistant thermally sprayed chromium carbide (Cr3C2)-based cermet coatings are nowadays a potential highly durable solution to allow traditional fluidized bed combustors (FBC) to be operated with ecological waste and biomass fuels. However, the heat input of thermal spray causes carbide dissolution in the metal binder. This results in the formation of carbon saturated metastable phases, which can affect the behavior of the materials during exposure. This study analyses the effect of carbide dissolution in the metal matrix of Cr3C2-50NiCrMoNb coatings and its effect on chlorine-induced high-temperature corrosion. Four coatings were thermally sprayed with HVAF and HVOF techniques in order to obtain microstructures with increasing amount of carbide dissolution in the metal matrix. The coatings were heat-treated in an inert argon atmosphere to induce secondary carbide precipitation. As-sprayed and heat-treated self-standing coatings were covered with KCl, and their corrosion resistance was investigated with thermogravimetric analysis (TGA) and ordinary high-temperature corrosion test at 550 °C for 4 and 72 h, respectively. High carbon dissolution in the metal matrix appeared to be detrimental against chlorine-induced high-temperature corrosion. The microstructural changes induced by the heat treatment hindered the corrosion onset in the coatings.

Chlorine-induced high temperature corrosion of Inconel 625 sprayed coatings deposited with different thermal spray techniques

Ni-based coatings of the type Inconel 625 sprayed with high-kinetic spray processes are applied as protective coatings in many industrial fields where high corrosion resistance is required. High-velocity oxygen-fuel (HVOF) and arc spray are common thermal spray methods used in the industry of power generation. Conversely, high-velocity air-fuel (HVAF) and cold spray are nowadays technologies of rising interest because of their possibilities to create highly dense and low oxidised metallic coatings. This study aims to assess the effect of the different high-kinetic spray systems on chlorine-induced high temperature corrosion protection of Inconel 625 coatings. The coatings were exposed for 168h to the test condition of 550°C under KCl salt deposits in 12% humidity air atmosphere. All the coatings provided effective protection to the substrate with the HVOF and arc sprayed coatings being the most resistant. The coatings were subjected to chlorine induced active oxidation and showed the typical layered structure of the external oxide deposit with chlorine detected at the coating/oxide interfaces. Signs of internal degradation were observed and were attributed to the penetration of chlorine through particle and splat boundaries. Chlorine was detected in some cases up to a depth of 200μm from the surface.

Preventing the chlorine-induced high temperature corrosion in power boilers without loss of electrical efficiency in steam cycles

The installation of combustion plants for waste and biomass with a connected boiler and steam cycle brought forth the problem of high temperature corrosion in the steam generators. This phenomenon originates from the composition of these fuels and in particular from the molar ratio of sulphur to chlorine, which is in the range of 2 and lower. Therefore, it is necessary to observe several demands on the construction and design of steam generators in order to prevent this sort of corrosion. All of these requirements arise from the limitation of the heating surface wall temperature as a function of the corresponding flue gas temperature and the gas velocity at the heat exchanger tube. It is, therefore, paramount to place the heating surfaces in the appropriate boiler areas to meet the temperature limits. The demands on steam generators to prevent high temperature chlorine corrosion are presented in this present work. Furthermore, one possible process design is presented, which in turn offers the possibility to operate a steam cycle at high pressure levels without the risk of high temperature corrosion or exceeding the limit for the final wetness at the steam turbine exit. This comparison points out that the new steam cycle gains the highest electrical efficiency when compared with two conventional cycles that meet the same goals.

The influence of alloying elements on the chlorine-induced high temperature corrosion of Fe-Cr alloys in oxidizing atmospheres

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The influence of alloying elements on the chlorine-induced high temperature corrosion of Fe-Cr alloys in oxidizing atmospheres

The effect of the alloying elements Al, Cr, Mn, Mo, Si and Ti on the corrosion behaviour of ferritic Fe-15Cr model alloys was studied in a N2/He-5 vol.% O2 gas mixture with and without additions of 500–1500 vppm HCl at 600°C. The main corrosion mechanism is “active oxidation”, characterized by the formation of volatile metal chlorides at the metal/oxide interface. Volatilization and subsequent conversion of the chlorides into oxides results in the formation of porous and poorly adherent oxide scales. Large mass gains were observed for Fe-15Cr, Fe-35Cr and Fe-15Cr with additions of 5 wt.% Ti, 10 wt.% Mn or 10 wt.% Mo. The specific morphology of the corrosion products depends strongly on the alloying elements. For the Fe-Cr alloys, a model for the formation of the scales, which are characterized by alternating dense and porous layers, is presented. The addition of 5 wt.% Si or Al to Fe-15Cr leads to much better corrosion resistance by the formation of protective Cr2O3/Al2O3-layers, however in the case of Al addition the behaviour depends strongly on the experimental conditions, as surface treatment and flow velocity. In Fe-15Cr-10Mo preferential removal of the more reactive metals Fe and Cr was observed resulting in a Mo-enriched porous metal zone underneath the metal-oxide interface. The effect of carbon on the corrosion behaviour was examined by addition of 0.3–0.8 wt.% C to the model alloys. Cr-rich M23C6-carbides were attacked preferentially while Mo-rich M6C-carbides are very stable relative to the matrix and the attack occurs in regions surrounding the carbides. Der Einfluß von Legierungselementen auf die chlorinduzierte Hochtemperaturkorrosion von Fe-Cr-Legierungen in oxidierender Atmosphäre Der Einfluß der Legierungselemente Al, Cr, Mn, Mo, Si und Ti auf das Korrosionsverhalten ferritischer Fe-15Cr-Modellegierungen wurde in einer N2/He-5 vol.% O2 Gasmischung mit und ohne Zusatz von 500–1500 vppm HCl bei 600°C untersucht. Der wesentliche Korrosionsmechanismus ist die „aktive Oxidation“, bei der sich flüchtige Metallchloride an der Metall/Oxid-Grenzfläche bilden. Verdampfen und anschließende Umsetzung der Chloride in Oxide führt zu porösen und schlecht haftenden Oxidschichten. Hohe Massenzunahmen wurden beobachtet bei Fe-15Cr, Fe-35Cr und Fe-15Cr mit Zusätzen von 5 gew.% Ti, 10 gew.% Mn oder 10 gew.% Mo. Die spezifische Morphologie der gebildeten Oxidschichten hängt stark von den jeweiligen Legierungselementen ab. Im Falle der Fe-Cr Legierungen wird ein Modell für die Bildung der Oxidschichten, die aus abwechselnd kompakten und porösen Schichten bestehen, vorgestellt. Der Zusatz von 5 gew.% Si oder Al führt zu stark verbesserten Korrosionswiderständen durch die Bildung von schützenden Cr2O3/Al2O3-Schichten; im Falle des Aluminiums ist dies allerdings kritisch abhängig von den experimentellen Bedingungen, wie Oberflächenbearbeitung und Strömungsgeschwindigkeit. Bei Fe-15Cr-10Mo wird eine bevorzugte Reaktion der reaktiveren Metalle Fe und Cr beobachtet, was zu einer Mo-angereicherten porösen Metallzone unterhalb der Metall/Oxid-Grenzfläche führt. Der Effekt von Kohlenstoff auf das Korrosionsverhalten wurde durch Zulegieren von 0,3–0,8 gew.% C zu den Modellegierungen untersucht. Cr-reiche M23C6-Karbide werden relativ zur Matrix bevorzugt angegriffen, während Mo-reiche M6C-Karbide sehr beständig sind und der Angriff bevorzugt in den umgebenden Metallbereichen erfolgt.

Chlorine-Induced High Temperature Corrosion: The Effect of Chlorine on Solid State Diffusion. A Theoretical Approach

Chlorine-Induced High Temperature Corrosion: The Effect of Chlorine on Solid State Diffusion. A Theoretical Approach

Chlorine-Induced High Temperature Corrosion: II. The Tedmon Equation as a Theoretical Approach of the Kinetics

Chlorine-Induced High Temperature Corrosion: II. The Tedmon Equation as a Theoretical Approach of the Kinetics

Chlorine-Induced High Temperature Corrosion: I. Metals and Alloys - A Review

Chlorine-Induced High Temperature Corrosion: I. Metals and Alloys - A Review