Role of Conductive Corrosion Products in the Protectiveness of Corrosion Layers

Abstract

In carbon dioxide (CO 2

Analysis of the corrosion scales formed on API 5L X70 and X80 steel pipe in the presence of CO2

“…These differences affect not only the mechanical properties of the steel but also its corrosion rate 4,12,17 . The literature indicates that growth of an FeCO 3 film is facilitated in steels with a ferrite-pearlite structure due to better anchorage of the carbonate deposits which adhere to the metal surface 5,[23][24][25][26] . The explanation is based on the fact that ferrite located within the pearlitic matrix is dissolved and the deposit of carbonate is thus anchored between the remaining plates of cementite exposed at the surface.…”

“…Within those areas for which the corrosive medium was deposited from the vapour, the CO 2 corrosion process would occur by the mechanisms described by Li et al 5 and Crolet et al 23 . The results of the present study indicate, however, that the quantity of solution present on the metal surface was insufficient to permit the formation of protective iron carbonate layers.…”

“…Dissolved HCO 3 -ions are dominant depolarizers, and deprotonated to form the 23 , at pH 6, the transport capacity of acidity via the highly mobile H + (or H 3 O + ) ions is negligible compared to the indirect effect of diffusion of quantities of mM/L of dissolved CO 2 , even though mobility of the latter is low and the kinetics of the final hydration of CO 2 and dissociation of H 2 CO 3 are slow. Thus, to conserve a realistic physical meaning for each solubility product, they are written systematically in terms of the majority independent species, which can be transported directly.…”

“…Crolet et al 23 showed that a thin, porous ("empty") layer of the Fe 3 C in contact with the steel (analogous to the "skeletal" structure of undissolved cementite mentioned above) is sufficient to cause so-called internal acidification, thereby increasing the corrosion rates due to the formation of a non-protective FeCO 3 film on the steel. If a sufficiently high iron concentration exists in the test solution when the steel sample is immersed, then the FeCO 3 can readily precipitate on the metal, and the resulting layer is protective in nature.…”

Corrosion in the Oil and Gas Industry: An Increasing Challenge for Materials

“…The solubility depends on the solution pH, CO 2 partial pressure, and temperature. [43][44][45][46] This precipitate can act as a protective layer that reduces the uniform corrosion rate of the steel. However, under certain environmental conditions, when the FeCO 3 protective layer is partially destroyed, localized corrosion can take place:…”