Preoxidation for the protection of high-temperature alloys in environments of high sulfur and low oxygen potentials pertinent to gasification processes

Conference · · TMS (The Metallurgical Society) Paper Selection; (USA)

OSTI ID:5465615

Stott, F H; Chong, M F; Stirling, C A ^[1]

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1. UMIST, Manchester (England)

In many fossil-fuel gasification environments, which can be complex and of low oxygen but high sulfur and carbon potentials, the normally protective Al{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} or SiO{sub 2} scales on high-temperature alloys may not be able to form or may fail soon after formation, enabling severe, often catastrophic sulfidation corrosion to take place. An investigation of behavior in equilibrated H{sub 2}/H{sub 2}O/H{sub 2}S environments at 750 to 900 C has shown that preoxidation to develop substantial oxide scales can improve significantly the subsequent sulfidation resistance of such alloys. These oxide scales act as a barrier to the environment and the initial rate of metal degradation is low. However, penetration of the scale by sulfur-containing species results eventually in breakdown and subsequently more rapid attack. The period of protectiveness is influenced markedly by a number of factors, particularly the type of oxide scale, with Al{sub 2}O{sub 3} being much more effective than Cr{sub 2}O{sub 3}, the aggressiveness of the environment and the adhesion and mechanical integrity of the scale. In this paper, the relative performances of several Cr{sub 2}O{sub 3} - and Al{sub 2}O{sub 3}-forming alloys in the aggressive environments are considered and related to the possible mechanisms of oxide scale breakdown and to the conditions of preoxidation and pre-treatment. Eventual breakdown of the oxide scales results from sulfur penetration through localized paths, and the progressive development of less-protective sulfide ducts from the alloy/scale interface to the scale/gas interface. These ducts provide easy diffusion paths for metal ions to the scale/gas interface, leading to development and rapid growth of sulfides at the surface.

• OSTI ID: 5465615
• Report Number(s): CONF-840909--
• Conference Information: Journal Name: TMS (The Metallurgical Society) Paper Selection; (USA) Journal Volume: 56
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
010404* -- Coal
Lignite
& Peat-- Gasification
36 MATERIALS SCIENCE
360105 -- Metals & Alloys-- Corrosion & Erosion
ADHESION
ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
COAL GASIFICATION
COATINGS
CORROSION RESISTANCE
CORROSION RESISTANT ALLOYS
CORROSIVE EFFECTS
DECOMPOSITION
ELEMENTS
ENERGY SOURCES
FLUIDS
FOSSIL FUELS
FUELS
GASES
GASIFICATION
HYDROGEN
HYDROGEN COMPOUNDS
HYDROGEN SULFIDES
NONMETALS
OXIDATION
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PROTECTIVE COATINGS
SCALING
STABILITY
SULFIDATION
SULFIDES
SULFUR
SULFUR COMPOUNDS
TEMPERATURE DEPENDENCE
THERMOCHEMICAL PROCESSES
TRANSITION ELEMENT COMPOUNDS
VAPORS
WATER VAPOR