Corrosion of 12% Cr alloys with varying Si contents in a simulated dry-feed entrained slagging gasifier environment

Abstract

12%Cr steels are used in coal gasifiers for heat exchangers but because of their limited resistance to corrosion in low-oxygen, sulphur-containing atmospheres, their application is limited to the lower temperature regions and therefore any method of improving the resistance of this class of material would be well-received by industry. This paper gives details of a joint EPRI/IAM-JRC-Petten study in which a series of “model” alloys based on the 12%Cr class of material, with Si additions of 1.3 to 4%, have been exposed at 450°C in a reducing gas simulating that found in a dry-feed entrained slagging gasifier. Examination of corroded specimens has enabled the nature and morphology of the surface scales to be established as well as metal losses due to internal attack to be quantified. Further, initial results arising from tests concerned with the influence of Cl-containing ash deposits on selected alloys exposed to the same gas at 400°C are discussed, including the additional influence of both dry and moist down-time periods.

Keywords:

• 12%Cr steels
• Si additions
• heat exchangers
• reducing atmospheres
• corrosion
• sulphidation attack
• down-time corrosion