Corrosion and Hydrogen Permeation in H2S Environments with O2 Contamination, 1: Tests on Pure Iron at High H2S Concentration

Abstract

Materials selection in the oil and gas industry relies on engineering standards, such as NACE TM0177 and NACE TM0284, which stipulate that oxygen pollution should be avoided during materials testing in H 2 S-containing media. In this paper, we explore the manner in which traces of oxygen can modify the test solution chemistry and the corrosion of/ hydrogen permeation across iron membranes in H 2 S-containing solutions. Oxygen pollution is shown to strongly influence solution chemistry, through the introduction of sulfur-oxygen reaction products resulting in bulk acidification. Weight loss, electrochemical methods, and solution chemistry measurements conclude that iron corrosion rates in the presence of oxygen pollution are doubled, when compared against the control system (without oxygen pollution). Unexpectedly, despite a lower pH and higher corrosion rates in the oxygen-polluted H 2 S-containing solutions, the hydrogen permeation rate decreases monotonically, relative to the control. We discuss how this observation is most likely related to a disruption of sulfur adsorbates involved in hydrogen entry promotion.

Corrosion and Hydrogen Permeation in H2S Environments with O2 Contamination, Part 2: Impact of H2S Partial Pressure

“…The validity of its usage in such experiments is outlined in Part 1. 5 For the studied conditions, it is observed that average permeation currents diminish with decreasing P H 2 S (i.e., lower [H 2 S] aq and [H + ] aq ). Quite remarkably, and as already observed in the previous article, permeation efficiencies are close to 100% for all tests without O 2 contamination, albeit more scattering appears at 0.1 kPa H 2 S. For this test condition (0.1 kPa H 2 S without O 2 ), it is believed that corrosion current densities were overestimated, due to insufficient influence of the charge transfer resistance in the frequency range of impedance measurements (Figure 4[g]).…”

“…The relevant preparation and experimental procedures are detailed in Part 1. 5 Pure H 2 S (>99.5% H 2 S) and H 2 S/N 2 gas cylinders (10% H 2 S/balance N 2 ), (1% H 2 S/balance N 2 ), and (0.1% H 2 S/balance N 2 ) were used to establish the different partial pressures of 10 kPa, 1 kPa, and 0.1 kPa, respectively, in the tests. The partial pressure of water vapor at 24°C being 3 kPa, a strict calculation of H 2 S partial pressures leads to a 4% decrease in the reported values.…”

“…A more complex model, including a porous film contribution, had to be used to analyze EIS data obtained at 100 kPa H 2 S, as explained in details in previous articles. 5,14 From the charge transfer resistances determined from the EIS data above, it is then possible to present the evolution of instantaneous corrosion rates, with the application of the Stern and Geary relationship (B = 40 mV/decade used here) and Faraday's law. The results obtained are illustrated in Figure 5.…”

“…4 In the first paper of this series, it was shown how traces of oxygen exacerbate the corrosion of, but diminish the hydrogen permeation across, iron membranes exposed to 35 g/L NaCl saturated with H 2 S at 24°C and atmospheric pressure (partial pressure of hydrogen sulfide gas = 100 kPa) as a function of time over 3 to 4 weeks. 5 In this second paper, with the pH-P H 2 S diagram of ISO 15156 in mind, the study parameters are extended to lower applied P H 2 S , i.e., how the same O 2 contamination influences phenomena in solutions containing lower dissolved H 2 S. As done in the first paper, only model systems are considered here, with pure iron as the test material, the use of unbuffered test solutions, and H 2 S or H 2 S/N 2 mixtures used to control the acid gas concentration (no CO 2 ). As before, this study follows the evolution of the solution chemistries, and the effect on Fe corrosion and hydrogen uptake, as a function of time.…”

Corrosion and Hydrogen Permeation in H2S Environments with O2 Contamination, Part 3: The Impact of Acetate-Buffered Test Solution Chemistry

“…With regards the test gas, either pure H 2 S (> 99.5% H 2 S), or a pure H 2 S + O 2 mixture (using a separate O 2 gas line to mix in an appropriate amount to provide a dissolved oxygen concentration [O 2 ] aq of 300 parts per billion (ppb or µg/L) by weight) were used to represent 'O 2 -free' and 'O 2 -polluted' testing scenarios respectively. 7 All tests were conducted at atmospheric pressure at a temperature of T = 24°C for a period of 720 h.…”