Dissolution of iron during the initial corrosion of carbon steel in aqueous H₂S solutions

Abstract

PARAM H . TEWARI and ALLAY B. CAMPBELL. Can. J. Chem. 57,188 (1979). The dissolution of iron from carbon steel in aqueous H,S solutions has been studied as a function of time and temperature at 0.1 MPa H,S pressure using the rotating disc technique. The iron sulfide film formed on the disc surface has been identified by X-ray diffraction analysis. The solubility and dissolution rate of synthesized mackinawite, FeS,,_,,, have also been determined to help establish the mechanism of release of iron from carbon steel corroding in aqueous H2S solutions.The rate data have been analysed by an equation for a joint chemical and transport controlled process. At 22°C and 0.1 MPa H2S, the maximum rate of release of Fez+, obtained by extrapolating the data to infinite rotation speed, is 7.4 i 0.5 ~m o l / m 2 s. This is similar to the dissolution rate determined for synthesized mackinawite powders, but is 20 times faster than the rate of dissolution for troilite and more than 1000 times faster than the dissolution rates for pyrrhotite and pyrite. Thus, troilite and iron sulfide phases that form subsequently are not major contributors to Fe2+ release during the corrosion of carbon steel.At 22'C the diffusion coefficient for the FeSH+ ion is (1.4 i 0.2) x 1 0 m2/s and the activation energy of the diffusion process is 25 i 7 kJ/mol. The chemical reaction occurring at the surface has a n activation energy of 77 +_ 14 kJ,'mol.It is concluded that the release of iron from corroding carbon steel is governed by the dissolution rate of mackinawite, the initial corrosion product. This dissolution is controlled by the chemical reaction between mackinawite and H + and by the transport of the complexed FeSH' from the interface to the bulk solution.PARAM H . TEWARI et ALLAK B. CAMPBELL. Can. J. Chem. 57, 188 (1979). Faisant appel a la technique du disque rotatif, on a etudie la mise en solution du fer d'aciers au carbone dans des solutions aqueuses de H2S en fonction du temps et de la temperature, a une pression de 0.1 MPa de H,S. Gr2ce a une analyse par diffraction de rayons-)<, on a identifie le film de sulfure de fer qui se forme a la surface du disque. On a aussi determine la solu- jusqu'a une vitesse de rotation infinie est egal a 7.4 + 0.5 ynlol/mz s. Cette valeur est semblable au taux de dissolution determine pour des poudres de mackinawite rnais elle est 20 fois plus rapide que celle determinee pour la dissolution de la troilite et plus de 1000 fois plus grande que les valeurs correspondantes pour la pyrrhotite et la pyrite. Donc les phases du troilite et de sulfure de fer qui se forment subsequemment ne contribuent pas d'une f a~o n importante a la mise en liberte du Fe2+ au cours de la corrosion des aciers au charbon.A 22"C, le coefficient de diffusion de I'ion FeSH+ est (1.4 + 0.2) x m2/s et I'energie d'activation du processus de diffusion est 25 +_ 7 kJ/mol. L'Cnergie d'activation de la reaction chimique se produisant a la surface est 77 i 14 kJ/mol.On en conclut que la mise en liberte du fer par un acier au charbon soumis a u...

The Corrosion of Steel by Aqueous Solutions of Hydrogen Sulfide

“…Evidently, at high solution velocities (> ~ 2 msec -1) the scale is more readily sloughed off leading to enhanced apparent corrosion rates in some instances. These results complement those of Tewari and Campbell (24,25) who studied the corrosion of carbon steel using the rotating disk technique. In the laminar flow regime at 22~C, PH2S "--1 arm, these authors reported corrosion rates in the order of 10 gm -2 day -1, and concluded that the corrosion rate was controlled by the rate of the chemical reaction between mackinawite and hydrogen ion and by the transport of FeSH + ions to the bulk solution.…”

Magnetic sulfide-modified nanoscale zerovalent iron (S-nZVI) for dissolved metal ion removal

“…S9). The hydroxyl radicals may further favor the break of FeeS bonds in Fe 7 S 8 , as observed by a peak of FeSH þ at around 320 nm (Tewari and Campbell, 1979). The derived FeSH þ can react with Cd 2þ in solution (Eq.…”

H2S corrosion inhibition of an ultra high strength pipeline by carboxyethyl-imidazoline

“…thus, inversely proportional to the corrosion rate I corr , but with the necessary condition that a trend removal applied over an average baseline, as previously established [16]. It has been demonstrated that the noise signal provides information about the dynamics that occur on the surface of the electrode and about the type of corrosion that is occurring, either uniform or localized.…”

“…On the other hand, the lowest R p was obtained for the blank solution and with the addition of either 5 or 100 ppm of carboxyethyl-imidazoline. In solutions containing H 2 S, the corrosion of steel is generally accompanied by the formation of iron sulfide film [16,17]. The fact that R p decreased with time, suggests the non-protective nature of the corrosion products film.…”

“…However, after 4 h approximately, the semicircle diameter decreased as time elapsed, indicating an increase in the corrosion rate. In H 2 S-containing solutions, the corrosion process of iron and steel is generally accompanied by iron sulfide film formation [16,17]. Thus, the increase in the impedance is due to the growth of iron sulfide film.…”