We study the changes in the properties of 09H2S + 08Kh13 bimetal from the K-6 and K-2 columns of the 'LYNYK' Closed Joint-Stock Company after operation for 27 and 12 yr, respectively. At 20 and 200°C, the mechanical properties of 09H2S steel after operation are compared with the properties of the metal in the as-delivered state. It is shown that, the most informative parameters among the mechanical characteristics of the metal are σ, σ, and δ, and the complex quantity σ /σ. The relative narrowing ψ and impact toughness are insufficiently informative due to the significant spread of the data of measurements. The long-term operation of the bimetal results in the pitting corrosion of the inner surface of the column, corrosion cracking in the heat-affected zone of welded joints, and knife-line corrosion. It is shown that the theory of dislocations adequately explains the causes and mechanism of hardening of steels operating in corrosive media. [ABSTRACT FROM AUTHOR]