Hydrogen damage is a severe problem that refers to the degradation of mechanical properties of a metal caused by the presence of, or interaction with, hydrogen. The reduction of hydrogen ions is a source of atomic hydrogen. Hence, corrosion reactions, the application of cathodic protection and electroplating, etc., are major sources for introducing hydrogen into metals. During these hydrogen-generating processes, some of the reduced hydrogen may be absorbed on the metal surface and diffuse into the metals. [1][2][3][4][5] The presence of hydrogen in metals has a significant influence on the mechanical properties and electrochemical behavior of metals. For instance, increased hydrogen content results in the low stress fracture and plastic reduction of steels. 6,7 Dissolution of hydrogen in metals was proven to affect the general corrosion of metals 1,8 and to induce stress corrosion cracking 9,10 and pitting corrosion. 11,12 It is known that the nature of passive films on metals and alloys is an ultimate factor which controls their corrosion behavior. 13,14 Therefore, knowledge about electronic structure of the passive film is required for better understanding of the corrosion process. For this reason, much work has been devoted to the study of the electronic properties and chemical composites of passive films on metals and alloys. 13,[15][16][17][18][19] Most passive films formed on stainless steels behave like semiconductors. Based on the fact that the potential-dependent transpassive dissolution varies with the electronic properties of the passive film, Sato 20 proposed a breakdown mechanism of the passive film on metals: the electrochemical stability of a passive film strongly depends on the electron energy band structure in the film. Bohni, et al. 21 studied the semiconductive properties of the passive films on 304 SS using Mott-Schottky analysis and photoelectrochemical methods. They found the coincidence of the onset potential for pit nucleation with the flatband potential of passive film. Bianchi et al. 14 concluded that the high susceptibility of stainless steel to pitting nucleation was connected to n-type conductivity of the oxide film. Nevertheless, the reason for the existence of this correlation is still not clear, and little research has been done to investigate the effect of hydrogen dissolved in metals on electronic structures of passive films on metals. 22 In this work, the new experimental results on the reversion of the electronic properties of passive film induced by hydrogen dissolved in AISI 310 SS were presented. The experimental results were analyzed by taking into account the susceptibility of specimens to pitting corrosion with or without hydrogen and were interpreted by the band model of different conductivity types of passive films. ExperimentalThe test material was commercial 310 SS foil, 0.01 cm thick. The main composition (wt %) was 23.5 Cr, 18.4 Ni, 1.76 Mn, 0.70 Si, 0.15 Mo, 0.16 Cu, 0.09 Ti, 0.02 Nb, 0.06 C, 0.02 P, 0.02 S, and Fe in balance. The solution for hydrogen charging wa...

No abstract

No abstract

No abstract

CUI (corrosion under insulation) is among the key concerns for the integrity of process equipment and pipelines. Various measures to detect and fix the damages from CUI pose significant maintenance expenditures in hydrocarbons processing facilities. The key reason behind CUI is the limitation of thermal insulations to absorb the moisture and soak the underneath metal from wicking action. Other than CUI, trapped moisture in the soaked thermal insulations causes heat loss from process systems, thereby posing the risk of additional damage mechanisms and increased operating expenditures. This study addresses the impact of robust drain openings and insulation stand-offs on the CUI rate of carbon steel under four different testing conditions namely isothermal wet, isothermal wet-dry, cyclic wet, and cyclic wet-dry, respectively. Corroded specimens were further characterized using surface topography and scanning electron microscope. The impacts of temperature and moisture cycling on the corrosion attributes were also characterized using the linear polarization resistance method followed by an investigation of corrosion modes via optical microscopy. Insulation stand-offs in conjunction with robust drain opening resulted in the lowest corrosion rate. With insulation stand-offs and drain openings, the cyclic temperature conditions caused higher metal loss than that in isothermal conditions.

No abstract

Fluctuations of the corrosion potential (E corr ) and the corrosion current were analyzed in the time domain for type A516-70 carbon steel (UNS K02700) exposed to 0.5 M sodium bicarbonate (NaHCO 3 ) solutions containing sodium chloride (NaCl) of different concentrations. Fluctuations of E corr and current observed for pitting-type corrosion had a distinctly different pattern from those associated with crevice corrosion for this type of carbon steel exposed to these solutions. Sharp potential and current fluctuations with amplitudes approaching several millivolts and several tens of microamperes, respectively, were detected during the pitting process. The fluctuation of potential produced during pitting occurred around E corr , which was ≈ -250 mV SCE to ~ -280 mV SCE . As crevice corrosion proceeded, E corr slowly decreased from -250 mV to ~ -280 mV to ~ -480 mV. The corrosion current increased simultaneously. Then, E corr dropped sharply to values ~ -760 mV and remained at this value, while the coupling current from Working Electrode 1 to Working Electrode 2 rapidly decreased. Then, the current flowing direction reversed, and the current finally decayed to zero. The time dependence of E corr and current was explained by the crevice corrosion mechanism.

The effect of tempering conditions on the carbides in P110 casing steels with two different Cr compositions was studied. Local Mo and Cr concentrations varied from the nominal compositions by ≈± 0.05 wt-% Mo and ≈± 0.07 wt-% Cr. The size of the fine (<20 nm) MC carbides remained relatively unaffected by tempering. Fe-based carbides exhibited a large increase in mean log-normal size from 65 to 102 nm when tempered at 650 and 715°C for 45 min, respectively. This rapid carbide coarsening is attributed to the dissolution of M23C6 carbides at 715°C. Associated with this significant increase in carbide size was an increase in the rate of hardness reduction with increasing Hollmon-Jaffe parameter for temperatures above 650°C.