
Full text loading...
Category: Applied and Industrial Microbiology; Environmental Microbiology
Microbial Corrosion in the Oil Industry: A Corrosionist's View, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817589/9781555813277_Chap08-1.gif /docserver/preview/fulltext/10.1128/9781555817589/9781555813277_Chap08-2.gifAbstract:
In view of the scientific and technical challenges as well as the considerable economic stakes (amounting to millions of U.S. dollars), this chapter focuses on the recent developments on the corrosion of steel by sulfidogenic anaerobes. The corrosion layer is an active membrane where a looped interaction between the corrosion electrochemistry and the chemistry and transport of reactants and reaction products may significantly alter the composition of the local electrolyte at the corroding metal surface. A conductive layer is thus a corrosion layer containing a continuous network of an inert electronic conductor galvanically coupled to the metallic substratum. In the case of FeS and microbial corrosion, this merely electric effect is not thought to be decisive, since (i) all iron sulfides are more or less conductive and (ii) the most conductive one, pyrite, is also commonly associated with the best level of protectiveness, whereas corrosive layers usually contain mackinawite (formerly kansite), which is one of the less conductive sulfides. The mechanism of pitting corrosion has been widely documented for stainless steels in chloride media or other passive metals like Al or Ti alloys. However, since the protectiveness of corrosion layers is sensitive to an applied polarization, an equivalent process also exists for carbon and low-alloyed steels. A widespread ecological niche also includes all the low-temperature oil reservoirs where indigenous bacteria have survived, possibly since the original deposition of the biomass. Sulfate-reducing bacteria (SRB) thrive in many deaerated and sulfate-bearing environments, and in a latent state under aerated conditions.
Full text loading...
Physical structure of metals and aqueous solutions and illustration of anodic and cathodic reactions. (a) Transfer of metallic cations; (b) transfer of electrons.
Physical structure of metals and aqueous solutions and illustration of anodic and cathodic reactions. (a) Transfer of metallic cations; (b) transfer of electrons.
Distribution of electric charge ρ (a) and electric potential U (b) across the metal-solution interface.
Distribution of electric charge ρ (a) and electric potential U (b) across the metal-solution interface.
(a) Individual polarization curves; (b) notion of oxidizing power.
(a) Individual polarization curves; (b) notion of oxidizing power.
Experimental polarization curves for activation polarization (black curves) or diffusion polarization (grey curves) at OCP.
Experimental polarization curves for activation polarization (black curves) or diffusion polarization (grey curves) at OCP.
Sketch of the three families of corrosion layers: soluble (a), IC (b), and IA (c). In panel a, arrows indicate that corrosion products are transported mainly in the solid state. The dotted arrow in panel c indicates the precipitatable anion HS-.
Sketch of the three families of corrosion layers: soluble (a), IC (b), and IA (c). In panel a, arrows indicate that corrosion products are transported mainly in the solid state. The dotted arrow in panel c indicates the precipitatable anion HS-.
Pitting mechanism on carbon and low-alloy steels by a self-amplified protectiveness contrast between anodic and cathodic areas (a), with, respectively, an increase of the Fe2+ and HS- release on anodic (b) and cathodic (c) areas (as an example of a cathodic reaction fed by H2S only).
Pitting mechanism on carbon and low-alloy steels by a self-amplified protectiveness contrast between anodic and cathodic areas (a), with, respectively, an increase of the Fe2+ and HS- release on anodic (b) and cathodic (c) areas (as an example of a cathodic reaction fed by H2S only).
Field morphologies of pits (a) and pit nucleation (b).
Field morphologies of pits (a) and pit nucleation (b).
Illustration of the full sequence of pit initiation (A), pit nucleation (B), and final pit growth (C). The shadowing geometry is very similar on convex and concave surfaces, which may give an initial false impression of protruding hemispheres instead of hemispherical pits.
Illustration of the full sequence of pit initiation (A), pit nucleation (B), and final pit growth (C). The shadowing geometry is very similar on convex and concave surfaces, which may give an initial false impression of protruding hemispheres instead of hemispherical pits.
Electrochemical models of pit nuclei using coplanar (a) and face-to-face (b) electrodes.
Electrochemical models of pit nuclei using coplanar (a) and face-to-face (b) electrodes.
Relevant orders of magnitude for steel corrosion in various units
Relevant orders of magnitude for steel corrosion in various units