High temperature corrosion of iron-chromium alloys in sulfur-containing atmospheres

Technical Report · Mon Jul 01 00:00:00 EDT 1985

OSTI ID:5275812

Choi, S H

The corrosion behavior of iron-chromium alloys in sulfur-containing environments has been studied in controlled oxygen and sulfur partial pressures. The partial pressures were chosen to simulate the sulfur and oxygen activities in low-oxygen partial pressure locations such as those in fluidized bed combustors. The high-temperature metal surfaces are covered with a calcium sulfate deposit. It was found that the calcium sulfate coupled with local low oxygen activities induces sulfidation/oxidation corrosion. Although the sulfur activity in the atmosphere is important in determining whether or not sulfidation/oxidation corrosion took place, the development of the attack is much more sensitive to the actual SO/sub 2/ partial pressure. Discrete internal Cr-rich sulfide particles were formed in the underlying alloy below an inner Cr-rich oxide layer. The development of internal sulfides is followed by in-situ internal oxidation of the sulfides, instability of the interface between the scale and alloy, leading to the incorporation of fragments of the more noble metallic constituents in the scale, and finally the destruction of the ability of the alloy to regenerate the protective oxide. The reaction kinetics associated with this morphological development are of the breakaway type. Sulfidation/oxidation is a breakaway process. After breakaway, the metal oxidizes to form a non-protective characteristic two-layer oxide scale. It is shown that the breakaway can be correlated with the develoment of a ''critical microstructure''. The potential benefit of such an identification is that the prospect of breakaway can be identified by microstructural studies of specimens corroded for relatively short times, and may allow for quantitative modelling of breakaway.

• Research Organization: Lawrence Berkeley Lab., CA (USA)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5275812
• Report Number(s): LBL-20011; ON: DE85017655
• Resource Relation: Other Information: Portions of this document are illegible in microfiche products. Thesis
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
CHROMIUM ALLOYS
CORROSION
FLUIDIZED-BED COMBUSTORS
IRON ALLOYS
CALCIUM SULFATES
CHEMICAL REACTION KINETICS
OXIDATION
SCALING
SULFIDATION
SULFUR
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
CALCIUM COMPOUNDS
CHEMICAL REACTIONS
COMBUSTORS
ELEMENTS
KINETICS
NONMETALS
OXYGEN COMPOUNDS
REACTION KINETICS
SULFATES
SULFUR COMPOUNDS
360105* - Metals & Alloys- Corrosion & Erosion