Scale stresses during protective and breakaway corrosion of iron and rimming steel in CO2

Modelling carburisation in 9Cr-1Mo ferritic steel tube substrates in experimental CO2 atmospheres

“…In the early stages, the tubes are protected by a duplex oxide layer [6,7] consisting of an outer Fe 3 O 4 (with some Fe 2 O 3 at the gas-oxide interface), and inner Cr-rich mixed metal oxide which has a spinel structure. These layers have approximately the same thickness which is explained by the available space model (void-induced duplex oxide growth mechanism) [6][7][8][9][10][11][12][13][14][15][16][17][18] According to this model, the outer magnetite layer grows as the Fe ions, which are generated at the scale/metal interface, diffuse through the duplex layer to react with CO 2 at the scale/gas interface as follows 3Fe + 4CO 2 → Fe 3 O 4 + 4CO…”

“…The carburisation process, therefore, should be affected by gas transport through scale and reaction rate inside the voids at the scale/metal interface, and its progress is observed to increase with CO 2 partial pressure in the gas [23]. If carbon is released at a faster rate than can be absorbed by the metal, it will be trapped in the inner oxide increasing its porosity [9,10]. Young et al [26] found that in martensitic steels P92 and VM12 reacted with Ar-50 % CO 2 at 550…”

“…• C, no steady-state local equilibrium was established at scale/substrate interface up to 150 h, and the carbon concentration continued to rise there with time. Gibbs et al [10] suggested that in mild steel, breakaway begins when the metal surface becomes able to catalyse the Boudouard reaction (4) which occurs when sufficient amount of carbon concentrate at the oxide/metal boundary. When this stage is reached, gas composition at the interface becomes similar to the outside gas, and a rapid oxidation phase follows leading to breakaway.…”

Processing, Microstructure, and Oxidation Behavior of Iron Foams

“…The parabolic rate constant of the oxidation of the current Fe foam is calculated to be 5.0 9 10 À12 g 2 cm À4 sec À1 , which is comparable to those reported in other studies: 2.7 9 10 À11 and 2.0 9 10 À11 g 2 cm À4 sec À1 . [37,38] IV. SUMMARY AND CONCLUSIONS…”

“…9-Kinetics of static air oxidation at 823 K (550°C) for Fe foam; the dotted line represents the parabolic fit with the rate constant (k p~5 .0 9 10 À12 g 2 cm À4 sec À1 ) displayed in the figure. [37] 2:7 Â 10 À11 823 K (550°C), Wet CO 2 [38] (~20 vpm H 2 O) 2:0 Â 10 À11…”