Initial Stages in the Metal-dusting Process on Alloy 800

Röhnert, Daniel; Phillipp, F.; Reuther, H.; Weber, Till; Wessel, E.; Schütze, M.

doi:10.1007/s11085-007-9075-9

Cited by 18 publications

(28 citation statements)

References 23 publications

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“…(14)), the volume lost per unit area of the sample, V L /S, can be expressed as: (19) To obtain the volume of all the pits per unit area, V tot L /S, both sides have to be considered since their pitting kinetics were observed to be different:…”

Section: Model I: Growth Of N 0 Pits With a Spherical-cap Morphologymentioning

confidence: 99%

“…An alloy which can form such an oxide scale will be corroded when the scale fails to protect the material, due to cracks, spalls or other defects. The alloy will be degraded locally, via a pitting-type mechanism [4,8,9,19]. Even if pitting is always noticed, only few studies focus on this phenomenon [19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

“…The alloy will be degraded locally, via a pitting-type mechanism [4,8,9,19]. Even if pitting is always noticed, only few studies focus on this phenomenon [19][20][21][22][23]. Moreover, as far as the authors know, the kinetics of metal dusting by pitting has never been modelled, despite existing modelling efforts in other type of pitting corrosion in aqueous environments [24].…”

Section: Introductionmentioning

confidence: 99%

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Modelling of the kinetics of pitting corrosion by metal dusting

et al. 2015

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a b s t r a c tCommercial 800HT alloy was exposed to 49.1%H 2 -12.8%CO-3.1%CO 2 -1.6CH 4 -33.4%H 2 O gas at 21 bars and 570 • C up to 5000 h. Metal dusting attack by pitting was observed. The kinetics parameters were identified to be the incubation time, pit density and individual pit growth rate. These parameters were introduced in a nucleation-growth model to simulate the pitted surface area kinetics. This model was then extended to the volume considering several geometrical hypotheses. Considering only surface coalescence of the pits without their volume coalescence allowed to correctly reproduce the experimental mass loss kinetics. An even simpler conservative model was proposed for an easy lifetime modelling.

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Section: Model I: Growth Of N 0 Pits With a Spherical-cap Morphologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modelling of the kinetics of pitting corrosion by metal dusting

et al. 2015

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“…At low oxygen potentials and unit carbon activity, cast heat resisting alloys can form mixed scales of chromium oxide and carbide [89]. At higher carbon activities, mixtures of chromium-rich oxide and graphite are formed in the early stages of reaction observed [90] on Alloy 800.…”

Section: The Influence Of Surface Oxides On Metal Dustingmentioning

confidence: 99%

Recent advances in understanding metal dusting: A review

Young

Zhang

Geers

et al. 2011

Materials & Corrosion

127

101

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Recent experimental investigations have widened the understanding of metal dusting significantly. Microscopic observations have been used to dissect dusting mechanisms. Iron dusts by growing a cementite surface scale, which catalyses graphite nucleation and growth. The resulting volume expansion leads to cementite disintegration. Cementite formation on iron can be suppressed by alloying with germanium. Nonetheless, dusting occurs via the direct growth of graphite into the metal, producing nanoparticles of ferrite. This process is faster, because carbon diffusion is more rapid in a-Fe than in Fe 3 C. Austenitic materials cannot form cementite, and dust via formation of graphite at external surfaces and interior grain boundaries. The coke deposit consists of carbon nanotubes with austenite particles at their tips, or graphite particles encapsulating austenite. TEM studies demonstrate the inward growth of graphite within the metal interior. It is therefore concluded that the dusting mechanism of austenitic materials like high alloy Cr-Ni steels and Ni base materials is one of graphite nucleation and growth within the near surface metal. In all alloys examined, both ferritic and austenitic, the principal mass transfer process is inward diffusion of carbon. Alloying iron with nickel leads to a transformation from one mechanism with carbide formation to the other without. Copper alloying in nickel and high nickel content stainless steels strongly suppresses graphite nucleation, as does also an intermetallic Ni-Sn phase, thereby reducing greatly the overall dusting rate. A surface layer of intermetallic Ni-Sn Fe-base materials facilitates the formation of a Fe 3 SnC surface scale which also prevents coking and metal dusting. Current understanding of the roles of temperature, gas composition and surface oxides on dusting rates are summarised. Finally, protection against metal dusting by coatings is discussed in terms of their effects on catalysis of carbon deposition, and on protective oxide formation.

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“…Carbon monoxide from the gas atmosphere reacts at the metallic surface to form atomic carbon, which diffuses into the substrate. The metallic substrate supersaturates in carbon and therefore decomposes into a mixture of graphite, oxidic, carbidic, and metallic particles (“metal dust”) . This leads to the formation of pits and possibly loss of containment …”

Section: Introductionmentioning

confidence: 99%

The influence of alloying elements on metal dusting behavior of nickel chromium alloys and their statistical correlation

Hattendorf¹,

Hermse²,

IJzerman³

2019

Materials & Corrosion

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The focus in this study is on very metal dusting resistant nickel chromium alloys with a high content of chromium (in the range of 22 to 33 wt.%), additions of aluminum (between 0 and 3 wt.%) and variable iron content (between 0.1 and 15 wt.%). All samples were exposed up to 5693 h at 600 °C in a 37 vol.% CO, 7 vol.% CO2, 46 vol.% H2, 9 vol.% H2O atmosphere at a total pressure 20 bar. The differences between the samples in terms of mass loss, pit depth and incubation time to first pit are evaluated by a statistical analysis and discussed in dependence of alloy composition. Only samples with combined chromium plus aluminum content of about 30 wt.% or more and an iron content of 0.6 wt.% or less do not show any pit formation during the exposure time, even on the edges. In contrast, samples with a similar combined chromium plus aluminum content, but with a higher iron content, do show pit formation due to metal dusting corrosion.

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Initial Stages in the Metal-dusting Process on Alloy 800

Cited by 18 publications

References 23 publications

Modelling of the kinetics of pitting corrosion by metal dusting

Modelling of the kinetics of pitting corrosion by metal dusting

Recent advances in understanding metal dusting: A review

The influence of alloying elements on metal dusting behavior of nickel chromium alloys and their statistical correlation

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