Corrosion state of oil cracking reactors as the main factor of fire and explosion safety during their operation

Abstract

The corrosion and mechanical properties of the oil catalytic cracking reactor vessel made of stainless steel Y1-T (1X18N9T) after its operation for more than 60 years have been determined. The chemical composition of the reactor metal meets the requirements of GOST and involves the isolation of non-metallic inclusions of manganese sulfide in its structure, which cause the development of pitting, and chromium carbides, which are responsible for the propensity to intergranular corrosion. After long-term operation, the mechanical characteristics of the metal (tensile strength σb, yield strength σt, elongation δ, relative contraction Ψ), determined using cylindrical samples at a temperature of 20 °C (GOST 1497-84) and at an operating temperature of 465 °C (GOST 9651), on the breaking machine TC 110M-50, correspond to the standard values. Metallographic studies carried out using an optical microscope “Axio Observer Z1m « at magnifications of X25, X75, x125, X200, X250, X400, X500, x1000, X2000 showed that long – term operation of the metal at a temperature of 375…425 °C with periodic overheating up to 550…650 °C leads to the release of excess phases, namely, chromium carbides and titanium carbonitrides. The metal grain boundaries are enriched with Cr23C6 carbides, which cause a loss of resistance against intergranular corrosion. Corrosion pitting and weakened metal grain boundaries are promoters of the occurrence of corrosion cracks. The most dangerous areas of large-size equipment are welded joints and zones of thermal influence. A mandatory condition for fire and explosionproof operation of the refinery is periodic diagnostics of the corrosion state of the equipment in order to identify and timely eliminate potentially dangerous areas, the probability of which breaching with subsequent spillage and fire of oil and petroleum products is the highest.