Low oxygen environments in biomass gasification and the presence of chlorine in feedstocks can influence the corrosion rate of steel by affecting the formation of protective oxide scales. The effect of KCl on the high-temperature corrosion of low-alloyed steel (13CrMo4-5) under low oxygen partial pressure is investigated by KCl salt spray (0.1 mg·cm−2) and exposure to 3 vol% H2 + 30 vol% H2O + Ar (balance) at 500°C for up to 168 h. Specimens without KCl salt are exposed for reference. Specimens are characterized after exposure by mass change, SEM/EDS, and XRD. KCl-deposited specimens exhibit about 30% lower mass gain after exposure compared to non-sprayed specimens. Their scale shows a porous innermost layer and a denser layer on top. No Fe or Cr chlorides are identified. The specimens without salt exhibit a similar two-layered scale, with a porous inner Fe-Cr oxide, followed by a denser and thicker Fe-oxide above. KCl could potentially protect the surface from further degradation by physically covering the specimen, altering the scale morphology, and forming a less permeable barrier, hindering the transport of species through the scale. 

Firing waste wood in thermal power plants can lead to furnace wall corrosion due to corrosive elements such as chlorine, heavy metals, and alkali metals present in the fuel. This study investigates the influence of lead and chlorine on furnace wall corrosion of a low alloyed steel (16Mo3) and a nickel-based alloy (Alloy 625) during two field exposures using an air-cooled probe. Two two-week long test campaigns firing two different waste wood fuels (higher and lower lead and chlorine content) were carried out, exposing samples having metal temperatures in the interval 350-400 °C. The corrosion rates were determined using thickness loss measurements. The samples were examined using SEM/EDS/WDS and XRD techniques, to characterize the morphology and composition of the corrosion products. The findings suggest that higher lead and chlorine content in the fuel results in a higher corrosion rate for both materials; aggravated further above 370 °C. On 16Mo3 samples, iron oxides and chlorides, and chlorine-rich compounds are observed. Pits are observed on Alloy 625 samples, filled with nickel- and chromium-containing oxides mixed with corrosive species. The presence of lead compounds (e.g. lead molybdate) in connection to pits suggests active participation of lead in the corrosion process above 370 °C. 

Aggressive corrosion can occur when firing waste or bio-based fuels, due to the presence of high concentrations of heavy metals, alkali metals, and chlorides. These deleterious compounds deposit on furnace walls and can form mixtures that can rapidly accelerate corrosion. The effect of salts containing lead had not been studied extensively at temperatures lower than 400 °C in nickel-based materials. This study investigates the effect of the individual salts PbCl2 and KCl and their mixture on the high temperature corrosion of alloy 625 at 340 °C and 380 °C. Samples of alloy 625 were covered with individual salts or a salt mixture and exposed to high temperatures in an atmosphere of synthetic air, 20-vol% H2O, and 100 ppm HCl. The results show that the presence of individual salts does not induce observable corrosion attack on alloy 625 after 168 h at any tested temperature. The salt mixture did cause a severe corrosion attack at 380 °C, observed after 24 h of exposure. It is suggested that the salt mixture induces the formation of lead chromates that may prevent or disrupt the formation of a protective chromia scale. It is believed that a key part of the mechanism is the formation of eutectic melts by the interaction of the scale with the salt mixture. Thermodynamic equilibria calculations show that the first melting temperature of PbCl2 and KCl salt mixture after reaction with oxygen can be as low as about 382 °C, and even lower (357 °C) if chromates are present. 

Three FeCrAl alloys (APMT, EF100 and EF101) from Kanthal® and the reference Ni-Cr Alloy 625 were used as weld cladding materials on tube shields in the evaporator tube bank of a waste-fired combined heat and power plant. For each alloy type, the overlay welded tube shields were placed in both roof and floor positions within the evaporator for 6 months. The metal-loss rate, the microstructure and hardness of the overlay welds before and after exposure and the corrosion products were analysed. The results showed higher metal-loss rates in the welds placed in the roof position, confirming heterogeneities in the evaporator bank environment. Alloys were ranked from higher to lower erosion–corrosion resistance as follows: APMT ≈ Alloy 625 > EF101 > EF100. The analysis of the corrosion attacks showed a significant variation among the alloys, from a primarily homogeneous corrosion attack on APMT to intergranular corrosion in EF100 and pit formation in EF101. 

Copper is the intended canister material for the disposal of spent nuclear fuel in Sweden. At repository depth the groundwater may contain dissolved sulfide. The main goal for this work is to study the tendency for stress corrosion of copper in sulfide solutions and examine the influence of various experimental parameters on stress corrosion. Slow strain rate testing was performed on copper test rods in solutions with 1.0 mM sulfide. The pH was kept near neutral with phosphate or borate buffer. The test matrix included variations in temperature, strain rate, and duration of the tests as well as salt and buffer concentrations. Cross-sections of the specimens after testing were investigated using scanning electron microscope/energy dispersive X-ray spectroscopy detector. Stress–strain curves do not reveal any signs of stress corrosion. However, intergranular corrosion in the shape of crack and pit-like features developed in all tests with 1.0 mM sulfide. The length of the deepest features in all these tests was of the same order of magnitude (10–20 µm). The suggested mechanism proposes that crack-like features originate at the surface of the copper metal from the oxidation of grain boundaries that behave as slightly less noble. © 2023 The Authors.