Corrosion of cast iron sections of gas-collecting bells of EcoSoderberg electrolyser

Abstract

The article presents results of the research of high-temperature gas corrosion of sections of EcoSoderberg electrolyzers’ gas-collecting bells (GSB) made of high-strength VCh50 cast iron with spherical graphite. The gravimetric method was used to study the specific mass losses of the sections due to corrosion. The microstructure of cast iron, structure, chemical and phase composition of corrosion products were studied using optical, electron microscopy and electron microprobe analysis. It was established that the specific weight loss of the sections during operation reaches 0.36 – 0.46 g/(cm2·month). Corrosion of cast iron sections of EcoSoderberg electrolyzers’ GSB is characterized by high unevenness by area. There are cases of decommissioning sections due to local through “burnouts” with a weight loss of 19 – 24 kg. With relatively uniform corrosion, the maximum allowable weight loss of the sections is 25 – 30 kg. To make predictive estimates based on experimental data, dependence of the sections’ mass loss on the operating time was obtained. It was found that the corrosion products of the sections consist of iron oxides and alloying elements of cast iron. Most samples are characterized by increased content of C, S, F, K, Al, and Na. Corrosion products have a pronounced layered structure and contain a large number of defects in the form of pores and cracks. The layers differ in chemical, phase composition, and macrostructure. All the studied samples are characterized by cyclic alternation of relatively dense layers of iron oxides Fe2O3 and Fe3O4 and more porous layers between them. The layers are characterized by increased content of C and F. Sulfur is evenly distributed over the thickness of corrosion products. The studied samples of corrosion products have high defectiveness, friability, large number of pores, cracks, discontinuities, and low adhesion to the surface of cast iron. This is due to the presence of phases and compounds with different coefficients of thermal expansion. The mechanism of corrosion products layers formation was established and scientifically proved.