This paper presents results from a series of experiments involving the intermittent exposure of several steels to a CO-based gas mixture containing 0.1% H2S for periods of up to 1000 hours. The flow of the gas was maintained at a rate sufficiently high to prevent equilibration of the mixture occurring at the reaction temperature of 550°C, thereby simulating conditions found in commercial coal gasification plants.
Five materials were selected for this study, i.e. three commercial alloys containing 9, 12 and 20% Cr and two specially cast 12%Cr “model” alloys with additions of 1% and 2% Si. Several specimens of each alloy were exposed at the same time; some samples were also coated with a Cl-containing ash mixture prior to exposure in order to study the influence of fly-ash deposits upon degradation. In addition, afler intermittently cooling the samples to room temperature, half were desiccated dry whilst
the remainder were placed in moisture-saturated air at 30°C in order to simulate conditions arising during periods of plant down-time, i. e. down-time corrosion (DTC). Corrosion kinetics are presented in terms of weight change and metal loss measurements indicating the significant improvement accompanying the addition of 1-2% Si to the basic 12%Cr
composition. The contributions of ash deposits and periods of moist down-time are also discussed. Kevwords: corrosion, alloy steels, Si-content, non-equilibrium gas, ash-deposits, down-time periods