Mechanisms of simultaneous sulfidation and oxidation of FeCr and FeCrNi-alloys and of the failure of protective chromia scales

Lobnig, R. E.; Grabke, H. J.

doi:10.1016/0010-938x(90)90211-m

Cited by 51 publications

(21 citation statements)

References 26 publications

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“…Such spinel appears to be permeable for carbon since the carbon signal stays high throughout the oxide into the metal phase. Such spinel also is permeable for sulfur [51] as shown by tracer studies, probably due to pores and channels.…”

Section: Protection By An Oxide Scalementioning

confidence: 99%

Metal dusting

Grabke

2003

Materials & Corrosion

178

120

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This introductory review paper summarizes shortly the research on metal dusting, conducted in the MPI for Iron Research during the last dozen years. Metal dusting is a disintegration of metals and alloys to a dust of graphite and metal particles, occurring in carburizing atmospheres at a C > 1 and caused by the tendency to graphite formation. The cause of destruction is inward growth of graphite planes into the metal phase, or in the case of iron and low alloy steels into cementite formed as an intermediate. The kinetics of metal dusting on iron and steels was elucidated concerning dependencies on time, temperature and partial pressures. High alloy steels and Ni-base alloys are attacked through defects in the oxide scale which leads to pitting and outgrowth of coke protrusions, after initial internal formation of stable carbides M 23 C 6 , M 7 C 3 and MC. A dense oxide layer prevents metal dusting, but formation of a protective Cr-rich scale must be favored by a fine-grain microstructure and/or surface deformation, providing fast diffusion paths for Cr. Additional protection is possible by sulfur from the atmosphere, since sulfur adsorbs on metal surfaces and suppresses carburization. Sulfur also interrupts the metal dusting mechanism on iron and steels, causing slow cementite growth. Under conditions where no sulfur addition is possible, the use of high Cr Nickelbase-alloys is recommended, they are largely protected by an oxide scale and if metal dusting takes place, its rate is much slower than on steels. Definition of metal dustingMetal dusting is a disintegration of metallic materials into a dust of fine metal particles and graphitic carbon. In the case of chromium steels and Ni-base alloys the corrosion product (coke) may also contain carbides and oxides. This corrosion phenomenon occurs in carburizing atmospheres, containing CO and/or hydrocarbons, at carbon activities a C > 1 which means that a tendency for graphite formation prevails (in equilibrium with graphite a C ¼ 1). Susceptible are metals and alloys which dissolve carbon, i.e. Fe, Ni and Co and their alloys. The carbon is transferred from the atmosphere and dissolved into the metal phase, at a C > 1 to oversaturation, leading to growth of graphite which destroys the materials. In the case of iron and steels, cementite is formed as an intermediate into which the graphite grows [1 -5]. Nickel and Ni-base alloys are disintegrated by direct inward growth of graphite [6 -9].Fe and Ni and low alloyed materials are attacked uniformly. In the most critical temperature range 400 -800 8C mostly chromia forming steels and Ni-based alloys are used, on these materials metal dusting starts locally, where the oxide scale fails, and leads to pitting and hole formation [3, 8 -12], see Fig. 1a. The corrosion product "coke" is growing out from the pits and holes, and mostly carried away in the fast flowing process gases, but observed in laboratory studies as outgrowing protrusions (Fig. 1b). Typical for Cr-steels and alloys is the zone with internal carbides (Fig. 1c...

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Section: Protection By An Oxide Scalementioning

confidence: 99%

Metal dusting

Grabke

2003

Materials & Corrosion

178

120

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“…[43][44][45][46] Heterogeneous noncatalytic coke formation is the most important coking mechanism since it operates practically over the entire cracking run. Coke formation via the homogeneous noncatalytic mechanism, so-called gas-phase coking, [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] can be neglected when light feedstocks are cracked.…”

Section: Influence Of Si Additives On Coke Formation 311 Influencmentioning

confidence: 99%

Influence of Silicon and Silicon/Sulfur-Containing Additives on Coke Formation during Steam Cracking of Hydrocarbons

Wang

Reyniers

Geem

et al. 2008

Ind. Eng. Chem. Res.

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The influence of the combination of two Si-containing additives, BTMS and TEOS, with DMDS on coke formation during steam cracking has been evaluated both on a laboratory scale and in a pilot plant unit. Under the optimal presulfidation conditions (T ) 1023 K, H 2 O ) 20 g h -1, DMDS in H 2 O ) 750 ppm wt, duration ) 1 h), the combination of Si pretreatment + presulfidation + continuous addition of 2 ppm wt DMDS results in a decrease in the rate of coke formation up to 40% when hexane is cracked in the lab-scale unit. Under similar conditions in the pilot plant the coke formation is decreased by 70%, while the CO production decreases by more than 90%. Moreover, the suppressing effect on coke formation remains significant even after several coking/decoking cycles. Simulations of an industrial ethane cracker indicate that the application of Si-and S-containing compounds as additives for the suppression of coke formation can potentially double the run length of industrial steam crackers.

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“…For the 25Cr alloy, the creep strength in N 2 -0.1SO 2 is increased by pre-oxidation in Ar (gas condition (3)) similar to the test result in Ar (gas condition (2)). For Fe-25Cr-20Ni, however, the creep strength in gas condition (3) is lower than in the Ar-only condition (gas condition (2)). This difference is due mainly to the degradation of the pre-formed oxides during creep in N 2 -0.1SO 2 .…”

Section: The Influence Of Pre-oxidation On Mechanical Strengthmentioning

confidence: 82%

“…[1][2][3][4][5][6] The protectiveness of the oxide scales depends greatly on features of the scales, such as the amount of spinel oxides contained in the oxide layer and the adherence of the oxide scales. [2][3][4][5][6] Corrosion progresses rapidly when the preformed oxides are fractured by the deformation of the alloy substrates. 5 The fracture of pre-formed oxide scales, such as cracking or spalling, under mechanical loading are important features of high-temperature alloy industrial applications, where mechanical loads are applied to the alloy at elevated temperatures.…”

Section: Introductionmentioning

confidence: 99%

Influence of Pre-oxidation on the Corrosion and Mechanical Strength of Fe–25Cr and Fe–25Cr–20Ni Alloys at 973 K

Sohn

Narita

2006

Oxid Met

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The influence of pre-oxidation on the corrosion and mechanical strength of Fe-25Cr and Fe-25Cr-20Ni alloys was investigated in N 2 -0.1SO 2 at 973 K with and without mechanical loadings. About 0.1lm-thick Cr 2 O 3 scales formed on the Fe-25Cr alloy by pre-oxidation in Ar. However, spinel oxides of (Fe,Cr) 3 O 4 remained on the Cr 2 O 3 and voids formed at the oxide/metal interface on Fe-25Cr-20Ni after pre-oxidation in Ar. The preformed oxides are very effective in preventing corrosion of the alloy surfaces. The preformed oxides are also beneficial to increase the strength of the alloys in corrosive environments. The effects of pre-oxidation on Fe-25Cr are stronger than those of Fe-25Cr-20Ni due to the different characteristics of the preformed oxides.

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Mechanisms of simultaneous sulfidation and oxidation of FeCr and FeCrNi-alloys and of the failure of protective chromia scales

Cited by 51 publications

References 26 publications

Metal dusting

Metal dusting

Influence of Silicon and Silicon/Sulfur-Containing Additives on Coke Formation during Steam Cracking of Hydrocarbons

Influence of Pre-oxidation on the Corrosion and Mechanical Strength of Fe–25Cr and Fe–25Cr–20Ni Alloys at 973 K

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