JUSTIFICATION FOR THE SELECTION OF A HIGH-SILICON IRON- BASED ALLOY FOR THE MANUFACTURE OF RECTIFICATION COLUMN SECTIONS. REVIEW
DOI:
https://doi.org/10.15407/plit2026.02.039Keywords:
high-silicon cast iron, ferrosilicide, ЧС15, sulfurous acid, corrosion resistance, passivation, silicon dioxide, spheroidal graphite, molybdenum, nickel alloyingAbstract
Operation of distillation columns in sulfur dioxide drying plants is accompanied by extreme corrosive effects of concentrated sulfuric acid (H2SO4) and anhydrides at temperatures up to 100-120 °C. Conventional stainless steels in such conditions demonstrate unsatisfactory resistance, which leads to frequent emergency shutdowns. The use of high-silicon cast irons (ferrosilicides) is technologically justified, but requires strict justification of the composition and structure due to their high fragility. It has been established that for the formation of a continuous protective film of silicon dioxide SiO2 capable of self-healing, the silicon content in the ferruginous matrix should be 14.5–15.5% (grade ЧС15). A lower silicon content leads to pitting corrosion, a higher one to critical embrittlement of castings. It has been proven that traditional lamellar graphite is the main factor in premature destruction of the tsarg due to the «wicking effect» (capillary penetration of acid deep into the metal). It is recommended to switch to point or spherical graphite by modifying the melt, which reduces the corrosion rate by 3–5 times. To stabilize the passive state during temperature fluctuations and work with «dirty» technical acids, the feasibility of alloying with 1% Mo and 1% Ni (Fe15Si) has been substantiated. Molybdenum strengthens the oxide layer against the action of chlorides, and nickel refines the grain, improving the mechanical strength of flange joints. The introduction of an alloyed high-strength alloy instead of basic grades allows you to increase the equipment overhaul interval from 4 to 8–10 years. Despite the increase in raw material costs by 25–30%, the total cost of ownership is reduced by 35% due to the absence of emergency downtime and a decrease in the number of replacements of expensive column sections.
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