Permeation Current Research Articles

Hydrogen permeation behavior of X80 pipeline steel under alternating wet-dry environment in the South China Sea

The riser sections of offshore pipelines are subject to cathodic potentials, alternating wet-dry (AWD) cycles and stresses in the service environment. The hydrogen permeation of X80 offshore pipeline with different cathodic potentials, dry/wet ratios, and constant tensile stress in AWD environment were investigated by the self made experimental equipment, which includes the three modules, i.e., the constant stress loading, the two-component cell hydrogen permeation, and AWD environment. Results showed that hydrogen permeation current fluctuates with the AWD, which is different from that in the bulk solution. In one AWD cycle, the permeation increases in the wetting stage and decreases in the dry stage. The smaller the dry/wet ratio, the longer the hydrogen permeation current keeps high level which is caused by the dense corrosion product layer. The hydrogen permeation currents in the elastic stress are greater than those in the plastic deformation, and unstressed conditions is the smallest.

Enhanced resistance to electrochemical degradation and hydrogen permeation by grain boundary and strain engineering in cobalt-graphene oxide composite coatings

Cobalt (Co) and cobalt-graphene oxide (Co-GO) coatings were electrodeposited on mild steel. The Co-GO coating with an optimum volume fraction of GO (Co-GO-3) displayed significantly reduced corrosion current density (5.3 μA/cm2) compared to pristine cobalt coating (21.4 μA/cm2) in 3.5 wt% NaCl solution. Formation of a stable CoO passive oxide layer and a higher proportion of low energy grain boundaries (low-angle grain boundaries and CSL boundaries) contributed to the enhanced anti-corrosion properties. The Co-GO-3 coating also exhibited the lowest hydrogen permeation current, attributed to its higher fraction of relatively closed grain boundaries and presence of compressive strain within the coating.

Degradation study and diagnostic technology for Nafion membrane

Developing a fast diagnostic technology for membranes and accurately predicting the lifetime of membranes that can effectively reduce the manufacturing cost and overcome the technical barriers of proton exchange membrane fuel cell (PEMFC) lifetime. This paper focuses on developing an ex-situ accelerated chemical degradation method and investigating the impact of chemical degradation on membrane structure and fuel cell performance. The results show that voltage drop and hydrogen permeation current can detect the state online and predict the remaining lifetime of membrane electrode assembly (MEA). The aging rate is faster by three orders of magnitude than that of the published results by the established aging way. This study provides an additional decision for evaluating performance degradation and fuel cell system optimization, which could potentially lead to further improvements in the efficiency and durability of PEMFC systems.

Hydrogen Diffusion and Trapping Behaviour in DP Steels: An Electrochemical Hydrogen Permeation Study

Advanced high-strength steels (AHSSs) are widely used in the automotive industry as they possess high strength-to-weight ratio. This allows designing light vehicles with better passenger safety, lower fuel consumption, and CO2emissions. Dual-phase (DP) steels are very attractive among the AHSSs because of their optimal combination of high tensile strength (up to 1.2 GPa), high ductility (10 % or more), and good formability due to their two-phase microstructure (ferrite and martensite). However, the use of DP steel is associated with an increased risk of mechanical degradation in the presence of hydrogen environment, i.e., hydrogen embrittlement (HE). The HE susceptibility of DP steel is mainly determined by hydrogen entry, diffusion, and trapping events in the microstructure (i.e., hydrogen interaction with metal). There are various methods to study the above mechanism in metals like hydrogen charging-tensile test, thermal desorption spectroscopy, silver decoration, scanning kelvin probe microscopy, electrochemical hydrogen permeation, etc. Among these, electrochemical hydrogen permeation using Devanathan - Stachurski (DS) cell is a simple and most widely used technique.In this work, electrochemical hydrogen permeation was used to understand the role of microstructural features on hydrogen diffusion and trapping behaviour in DP-980 steel. It was identified that the phase fraction and its morphological features influence the hydrogen diffusion behaviour. The challenges in layout, design and integration of conventional DS cell into a tensometer and the effect of pre-strain (ex-situ) and tensile stress (in-situ) loading on hydrogen diffusion and trapping in DP-980 will be discussed. The applied elastic stress (i.e., 50 % of YS) during the permeation test resulted in a slight increase in Dapp from 5.4 ± 0.1 × 10- 7 to 5.9 ± 0.69×10-7 cm2s-1 and a slight reduction in NT from 1.08 ± 0.01 × 1021 to 1.0 ± 0.13× 1021 sites cm-3 compared to the no-stress condition. At 110 % of YS, the highest value of iss is 169 ±10.6 (µAcm-2) and a significant increase in the value of Capp to 3.6 ± 0.3 × 10-4 (molHcm-3 ), whereas no significant change in values of Dapp and NT were observed at 110 % YS compared to no stress and 50 % of YS. This could be due to the elastic deformation of martensite at 110 % of YS. The lattice expansion of martensite under elastic tensile stress can accommodate more interstitial hydrogen, thereby higher steady-state permeation current is observed. At 125 % of YS, the value of Dapp (2.86×10-7 cm2s-1) is approximately 50 % less compared to the value observed for the un-stressed specimen (5.4 ± 0.1×10-7 cm2s- 1). The value of NT (2.11×1021 cm-3) is approximately two times higher than that of the value (1.08×1021 cm-3 ). Plastic deformation of both ferrite and martensite results in increased dislocation density (hydrogen trap sites) at 125 % of YS. The sample failed during the hydrogen permeation test and when it is subjected to 125 % YS. It exhibited distinct fractographic features along the thickness of the sample. Quasi-cleavage and intergranular cracks were observed near the cathodic surface. Whereas, dimples and microvoids which are complete ductile features, were observed near the anodic surface. At 125 % of YS a significant decrease in the value of DL 0.6×10-6 cm2s-1 was observed. Whereas the value of NTrev increased to 4.0 ± 0.2×1019 cm-3 from 3.0 ± 0.15×1019 cm-3.An attempt was made to study the hydrogen transport behaviour at the local spot by appropriate modification of conventional DS cell. The fabrication challenges and the potential application of such an instrument will be elucidated.

The mechanism of inhibitive effect on hydrogen permeation of X70 steel by lanthanum microalloying: Enhanced kinetics of desorption

In this work, electrochemical hydrogen permeation tests were carried out to obtain the steady-state hydrogen permeation current of X70 pipeline steel in acid environment and alkaline electrolyte with applied cathodic overpotentials simulating the service conditions of pipelines. It is shown that La-microalloying can efficiently reduce the steady-state hydrogen permeation current density while maintaining the same mechanical performance. The experimental permeation data were fitted with Iyer-Pickering-Zamanzadeh (IPZ) and surface effect model to analyze the inhibitive mechanism on hydrogen permeation, and the results depicted that La element on the material surface greatly facilitates the desorption process of hydrogen atoms. In addition, the calculated hydrogen diffusion coefficient was found smaller after La microalloyed, which can be ascribed to the larger hydrogen trap density. It is suggested that La-microalloying can mitigate hydrogen damage of X70 pipeline steel in both acidic environment or under cathodic protection.

Effects of La3+ on the hydrogen permeation and evolution kinetics in X70 pipeline steel

The inhibitory effect of La3+ on the hydrogen permeation of X70 pipeline steel was investigated via steady-state hydrogen permeation current (i∞) through electrochemical hydrogen permeation tests. The experimental permeation data were fitted with a constant concentration model and Electrochemical Impedance Spectroscopy (EIS) tests were conducted to characterize the activity of Hydrogen Evolution Reaction (HER) after the optimization of electrochemically active surface area. Additionally, the kinetics of HER and the adsorption/desorption process is calculated by Iyer-Pickering-Zamanzadeh (IPZ) and surface effect models, of which the results demonstrate that the La3+ in the corrosion products could effectively reduce the rate of Volmer reaction and hydrogen adsorption process, and accelerate the process of hydrogen atom desorption, thus leading to the remarkable decrease in C0.

Ultra-thin h-BN doped high sulfonation sulfonated poly (ether-ether-ketone) of PTFE-reinforced proton exchange membrane

The high proton conductivity of proton exchange membrane under low humidification must be maintained. In this work, an ultra-thin reinforced membrane was prepared by using hexagonal boron nitride nanosheets (h-BN), high sulfonated poly (ether-ether-ketone) (sPEEK, DS = 81.4%), and expanded polytetrafluoroethylene (ePTFE) for low-humidification proton exchange membrane fuel cell (PEMFC). A sPEEK/PTFE-reinforced membrane was prepared using reasonable designing and processing methods without requiring special treatment for ePTFE. The [email protected]/ePTFE-reinforced membrane showed good proton conductivity, low hydrogen permeation current, and high cell performance. SEM confirmed the uniform h-BN dispersion in the ePTFE matrix membrane. Among the prepared samples, 0.5%[email protected]/PTFE-reinforced membrane exhibited the highest proton conductivity with 0.283 S/cm at 60 °C. Its peak power density was 567.7 mW/cm2, which was 16.6% higher than that of Nafion 212 (486.7 mW/cm2) under the same testing condition. All these results indicate that the [email protected]/PTFE composite membrane prepared with ultra-high sulfonation degree sPEEK has broad application potential in low-humidity PEMFC.

The effect of H2S and NaCl concentration on hydrogen permeation in high strength low alloy carbon steel C110

ABSTRACT The sulphide stress cracking of high strength low alloy (HSLA) carbon steel C110 is related to the hydrogen absorption process. The objective of this research is to evaluate the effect of adsorbed H2S and Cl− on hydrogen permeation in C110, by studying the responses of hydrogen permeation current and characteristic inductance under environment with different H2S activities and NaCl concentrations using electrochemical methods, including hydrogen permeation method and electrochemical impedance spectroscopy (EIS). The hydrogen permeation current measured in Devanathan–Stachurski cell suggests that the enhance effect of the adsorbed H2S on the hydrogen absorption follows an adsorption isotherm behaviour as a function of H2S activity in solution. The inductive response of EIS under different H2S activities shows consistency with hydrogen permeation results. The EIS results also indicate that the coverage of H2S was suppressed by Cl−. A good correlation about the effect of adsorbed Cl− is found between inductive response and hydrogen permeation current.

Effect of Surface Microstructure on the Hydrogen Permeation Behavior of Plasma-Nitrided AISI 4135 Steel

Hydrogen embrittlement is a serious problem for high strength steels. The reduction of hydrogen uptake by the formation of surface layers with low hydrogen diffusivity is thought to be effective in preventing hydrogen embrittlement. We reported that the plasma-nitrided surface layer composed of ε-Fe2-3N and γ’-Fe4N phases strongly inhibited hydrogen diffusion into the pure iron matrix.1) In this study, we controlled the microstructure of surface nitrided layers of an AISI 4135 steel by plasma nitriding, and investigated the hydrogen permeation behavior.AISI 4135 steel sheets of 1 mm in thickness were used as the specimens. Prior to plasma nitriding, the specimen surfaces were polished using a diamond past down to 1 μm. The plasma nitriding treatments were conducted in nitrogen-hydrogen atmospheres at 600 Pa for 3.6 ks. The temperature of the specimen surface was kept at 450 °C. Two types of nitrogen compound layers were formed on the specimen surface by changing the mixing ratio of nitrogen and hydrogen gases. One was composed of ε-Fe2-3N and γ’-Fe4N phases (specimen A), and the other was done of only γ’-Fe4N phase (specimen B). The compound layers of specimen A and B were 10 μm and 1 μm in thickness, respectively. In addition, the thicknesses of the nitrogen solid solution layers of specimen A and B were estimated to be ca. 270 μm and 210 μm, respectively.To investigate the effect of the surface microstructure on the hydrogen permeation through the specimens, the hydrogen permeation test using a conventional Devanathan-Stachurski cell was carried out. The nitrided surface was arranged in the hydrogen detection side. A Pd thin film was deposited on the specimen surfaces in the hydrogen detection side. The hydrogen detection side was polarized at 0.18 V vs. SHE in 0.1 M NaOH fully deaerated by pure Ar gas. The hydrogen entry side was polarized at −0.4 V vs. SHE in 0.1 M H2SO4. The hydrogen permeation test of specimen A reveals that the rise transient of the hydrogen permeation current was delayed and the steady state permeation current was significantly reduced. On the other hand, the hydrogen permeation behavior of specimen B was almost similar to that of the as-polished specimen. These results indicate that the nitrogen compound layer composed of ε-Fe2-3N and γ’-Fe4N phases inhibits the hydrogen permeation. Particularly, the existence of ε-Fe2-3N phase with the hcp structure is thought to be effective in preventing the hydrogen permeation.1) Y. Sugawara, I. Muto, and N. Hara, ECS Trans, 75(29), 43 (2017).

Effects of Ammonium Thiocyanate and pH of Aqueous Solutions on Hydrogen Absorption into Iron under Cathodic Polarization

To evaluate the susceptibility of steels to hydrogen embrittlement, it must be hydrogen charged and have its hydrogen content controlled before any mechanical testing. In this study, hydrogen permeation tests of an iron sheet were performed during potentiostatic hydrogen charging in various solutions containing ammonium thiocyanate to obtain a guideline for efficient hydrogen charging for a wide range of hydrogen contents. As the polarization potential shifted in the negative direction, the hydrogen permeation current increased before becoming almost constant. In all cases, besides when an aqueous sodium hydroxide solution was employed, the hydrogen permeation current increased due to the addition of ammonium thiocyanate. The effect of adding ammonium thiocyanate was enhanced as the aqueous solution pH was decreased. The hydrogen permeation current under various hydrogen charging conditions obtained in this study can be used as a reference for hydrogen charging of steels.

Influence of iron oxides and calcareous deposits on the hydrogen permeation rate in X65 steel in a simulated groundwater

The hydrogen permeation behavior of X65 steel was studied in a simulated Canadian groundwater (NS4) using a Devanathan-Stachurski cell. In the absence of a palladium coating on the detection side of the steel membrane, the hydrogen permeation current was suppressed by the growth of an oxide film on the steel. When a palladium coating was applied it was necessary to first remove the air-formed oxide from the steel surface which would otherwise control the permeation behavior due to its low hydrogen diffusivity. On the charging side of the membrane the deposition of CaCO3 and Mg(OH)2 enhanced hydrogen absorption into the cell leading to an enhanced permeation current.

(Invited) Effect of Rust on Hydrogen Uptake into Exposed Steels during Drying of NaCl Droplets

In recent years, high-strength steels have been widely used in many industrial fields such as automobiles and construction. However, hydrogen embrittlement (HE) of high-strength steels has been a great concern because HE susceptibility of the steels strongly relates to the strength of them. Since the steels are often used in atmospheric environments, hydrogen atoms generated by corrosion reaction are absorbed into steels and can cause HE. Therefore, to use the high strength steel safety, it is needed to clarify hydrogen absorption mechanism into steels in atmospheric environments. However, in atmospheric environments, corrosion reaction is considered to occur under wet/dry cyclic conditions. Especially, since corrosion product layers consisting of iron rust is formed during steel corrosion, they can affect the rates of both corrosion reaction and hydrogen uptake. In this study, the effect of rust on hydrogen uptake into steels is discussed based on the results of hydrogen permeation current and corrosion potential.A sheet of plain carbon steel (0.020 % C, 0.01 % Si, 0.018 % Mn, 0.015 % P, 0.007 % S, Bal. Fe) was used as a material. The size of steel sheet was 150 mmw x 75 mml x 0.8 mmt. Both surfaces of the sheet were ground with SiC papers down to P500 grit and then degreased. The steel sheet was exposed for 1 month at Choshi exposure test site of Japan weathering test center (Chiba, Japan). It was located about 4 km far from the coast.The steel sheet after the exposure test was covered with iron rust completely. The sheet was cut into small coupons of 25 mmw x 25 mml x 0.8 mmt. One side of coupon surfaces working as hydrogen-detection side was ground with SiC papers down to P1200 grit to remove iron rust. Then this side was electroplated with Pd ca. 400 nm in thickness. For other side of the coupon surfaces for hydrogen-entry side, iron rust was removed partly. This side of the steel surfaces was subjected to a wet/dry corrosion test. A sample was finally prepared after both surfaces were cleaned with Milli-Q water (18 MW cm at 25 oC). The exposed surface area of the sample was fixed about 1 cm2 for both hydrogen-entry and hydrogen-detection sides by coating with rubber-type masking agent.Hydrogen uptake behavior of rusted steel was investigated by Devanathan-Stachurski method [1]. A coupon of rusted steel was set in this cell. Test solution filled in the hydrogen-detection-cell was 0.1 M NaOH. In this cell, Pd-electroplated surface was polarized at a constant potential of +0.1 V vs. Ir wire. On the opposite side of steel surfaces for hydrogen-entry side, a 30-mL droplet of 10 mM NaCl was placed on the rusted steel to measure hydrogen permeation current. During the drying of the droplet, corrosion potential for the rusted steel coupon was measured with a home-made Kelvin probe (KP) simultaneously with hydrogen permeation current [2-4].On the exposure test at Choshi, iron rust was formed on the whole steel surface. XRD and FT-IR analysis revealed that the iron rust consisted mainly of a- and g-FeOOH. In addition, amorphous rust may be involved in the rust.Hydrogen uptake behavior of the rusted steel with various percentages of the rusted area was observed during the drying of NaCl droplet. The amount of hydrogen entry was calculated by integrating the transient of hydrogen permeation current during the drying. The amount of hydrogen entry, N H depended on the percentage of rusted area were . For N H of 0 % of rusted area a bare steel before exposure test was used. The N H was increased with decreasing the percentage of rusted area. When the percentages of the rusted area were 90 and 98 %, corrosion potentials during drying of a NaCl droplet were more negative than that of 100 %. The change of corrosion potential may affect the increase of N H. A.V. Devanathan, A. Stachurski, Proc. Roy. Soc., A270, 90 (1962).Stratmann, H. Streckel, Corros. Sci., 30, 681 (1990).Stratmann, H. Streckel, Corros. Sci., 30, 697 (1990).Stratmann, H. Streckel, K. T. Kim, S. Crockett, Corros. Sci., 30, 715 (1990)

The dependence of anti-corrosion behaviors of iron sulfide films on different reactants

As the product of hydrogen sulfide corrosion, iron sulfide compound can be used as hydrogen permeation barrier. In this study, chemical vapor deposition was used to synthesize iron sulfide films on the surface of X80 steel with different sulfur sources, and the effects of different sulfur sources on the products were studied. The film was characterized by its morphology, composition and performance. The results show that the hydrogen resistance of our product and the bonding degree between the substrate and the film are strongly relevant with the compactness of the films. When we used TBDS as sulfur source, the highest impendance and the smallest hydrogen permeation current (0.53 μA/cm2) was obtained, which is due to the better adhesion and dense structure compare to the other two sulfur sourses.

Inhibition of Hydrogen Entry into Pure Iron By Formation of Nitrogen Solid Solution Layer in the Surface

Hydrogen embrittlement is a serious problem for steels such as high strength steels. In order to prevent hydrogen embrittlement, the inhibition of hydrogen entry into the steel matrix is one of important subjects. The formation of surface layers with low hydrogen diffusivity is thought to be effective in inhibiting the hydrogen entry into the steel matrix. In this study, we formed nitrogen solid solution layers containing iron-nitrogen martensite and retained austenite phases on the surface of pure iron specimens by plasma-nitriding and subsequent quenching, and investigated the hydrogen permeation behavior. Pure iron sheets of 1 mm in thickness were used as the specimens. Prior to the nitriding treatment, the specimen surfaces were polished using a diamond past down to 1 μm. The plasma nitriding treatments were carried out in a nitrogen-hydrogen atmosphere at 370 Pa for 600 s. The temperature of the specimen surface was kept at 873 K by controlling the supplied DC voltage. After the plasma nitriding, the specimens were quenched from 1073 or 1273 K for 180 s. In the case of the quenching from 1273 K, an iron-nitrogen martensite phase was formed in the surface. The thickness of the surface layer was over 100 µm. Iron-nitrogen martensite and retained austenite phases were formed in the surface of the specimen quenched from 1073 K. The thickness was ca. 50 µm. To investigate the effect of the nitrogen solid solution layers on the hydrogen permeation behavior through the specimens, a hydrogen permeation test using a conventional Devanathan-Stachurski cell was carried out for 3.6 ks. The nitrided surface was arranged in the hydrogen entry side. Pd of 200 nm in thickness was deposited on the specimen in the hydrogen detection side. The hydrogen detection side was polarized at 0.2 V vs. SHE in 0.1 M NaOH fully deaerated by pure Ar gas. The specimen in the hydrogen entry side was polarized at −0.8 V vs. SHE in 0.1 M H2SO4. The hydrogen permeation tests reveal that the permeation current of the specimen quenched from 1273 K was smaller than that of as-polished one. The surface martensite phase seems to suppress the hydrogen permeation. In addition, no permeation current of the specimen quenched at 1073 K was detected. This is because the hydrogen diffusivity in the austenite phase is much lower than the ferrite phase due to high solubility limit in the austenite phase. The surface layer containing the austenite phase is found to be effective in inhibiting the hydrogen entry into the matrix.

Combined effect of cathodic potential and sulfur species on calcareous deposition, hydrogen permeation, and hydrogen embrittlement of a low carbon bainite steel in artificial seawater

Calcareous deposition, hydrogen permeation, and hydrogen embrittlement of E690 steel in thiosulfate-containing artificial seawater (ASW) under cathodic polarization are investigated. Sulfur species in acidic ASW eliminate the aragonite precipitation, attributed to the variation of cathodic reaction, favorable adsorption of HS− and enhanced hydrogen evolution. The maximum permeation current was achieved at −850 mVSCE due to the change of interfacial pH and promotion ability of sulfur species. Hydrogen embrittlement susceptibility increases linearly with logarithm increase of hydrogen concentration, while the preferential cracking pathway evolves from lath boundary separation at low hydrogen concentration to prior austenite grain boundary failure at high concentrations.

Hydrogen diffusion in low alloy steels under cyclic loading

Abstract The aim of this work is to analyze hydrogen transport in a low alloy steel by applying the electrochemical permeation technique to matrices subject to cyclic loading conditions, up to the yield strength and beyond this limit. The results indicate that, with an increase in the applied maximum stress, a decrease in the apparent diffusivity takes place, along with a marked and instantaneous reduction of diffusing hydrogen in the lattice and an increase in hydrogen solubility. An effect on the permeation current was observed, together with a variation of hydrogen diffusion kinetics ascribable to the activation on new trapping sites, with an appreciable effect under cyclic loading already at 55% of the yield limit, which becomes more relevant in the plastic domain.

Cracking mechanism in API 5L X65 steel in a CO2-saturated environment

Hydrogen charging in low alloy steels poses a significant problem in the oil and gas industry. Detrimental hydrogen effects are not commonly expected in CO2 aqueous environments. However, the acid nature of these environments and the high corrosion rates expected justify the assessment of cracking susceptibility of carbon steel in a CO2-saturated environment as presented in this work. The focus of this investigation is to understand how different surface films/corrosion products influence the hydrogen permeation and cracking mechanism of an API 5L X65 carbon steel in a saturated CO2 environment. The experiments were carried out to assess hydrogen permeation at open circuit potential on steel samples which were either wet-ground, or pre-filmed with iron carbide (Fe3C) rich or iron carbonate (FeCO3) layers. Tafel measurements were also performed to determine the effect of the surface composition on the cathodic reactions. Slow strain rate tests (SSRT) were conducted in order to evaluate the effects of hydrogen on the cracking mechanisms of the steel in this sweet environment. Results indicated that at open circuit conditions, Fe3C was able to increase the steady state hydrogen permeation current due to accentuation of the cathodic hydrogen-evolution reaction. Although FeCO3 suppressed the cathodic reaction at the steel surface, the development of the protective and densely packed crystalline layer increased hydrogen uptake marginally from that of the ground steel reduced. SSRT indicated a very moderate loss of ductility in wet-ground and FeCO3 steel surface conditions. However, a more significant reduction in area was observed in the tests carried out on Fe3C rich samples. These results imply that a corroded API 5L X65 steel surface in a CO2 rich environment can enhance the hydrogen embrittlement (HE) susceptibility and as such, hydrogen permeation susceptibility needs to be considered in material selection.

Hydrogen Absorption Behavior of Pre-Rusted Steels under an NaCl Droplet

In this study, we investigated the hydrogen absorption behavior of pre-rusted steel in an NaCl droplet by measuring the hydrogen permeation current and corrosion potential. To prepare the pre-rusted steel, a 30-μL droplet of a 0.1-mol/dm3 NaCl solution was placed on the surface of steel and exposed to wet-dry cyclic conditions by changing the relative humidity (RH) repeatedly from 40% to 95% at a constant rate of 27.5%/h and 298 K. The hydrogen permeation current and corrosion potential of the pre-rusted steel were measured during the drying of an electrolyte droplet using an electrochemical hydrogen permeation test and the Kelvin probe (KP) technique, respectively. The corrosion potential of the pre-rusted steel shifted in the negative direction simultaneous with the evolution of the hydrogen permeation current during the drying of the droplet. The hydrogen permeation current increased with the number of wet-dry cycles in the early stages of the rusting process, which related to the negative shift in corrosion potential. As the whole surface of the steel was covered with iron rust in the later stages of the rusting process, the corrosion potential shifted in the positive direction and the hydrogen absorption current decreased gradually.

Novel Methodology for the Selection, Dosing and On-Line Control of Corrosion Inhibitors for Industrial Acid Pickling

A novel methodology based on electrochemical hydrogen permeation tests is proposed to study the efficiency of commercial inhibitors for industrial acid pickling of iron and mild steels. Weight loss measurements and hydrogen permeation tests have been carried out in order to compare the sensitivity of different techniques to variations of low inhibitor dosages. It has been found a close dependence between low amounts of filming inhibitors and hydrogen uptake in the metallic surface with related permeation currents. The high sensitivity of permeation currents may be very useful to establish and also control the optimum amount of active substances in industrial pickling baths, with related cost savings. The implementation of the proposed methodology to improve the control of industrial pickling plants is also envisaged, since it would be possible to improve both sensitivity and time response of experimental permeation curves.

Hydrogen Entry into Steel Exposed in an Outdoor Environment

Introduction In recent years, high-strength steels have been widely used in many engineering fields such as automobiles and construction. However, hydrogen embrittlement (HE) of high-strength steels has been a great concern because HE susceptibility of steels strongly relates to the strength of them. Especially, high-strength steels are often used in atmospheric corrosion environments and hydrogen atoms are generated by corrosion reaction. Some of the generated hydrogen atoms are absorbed into steel and they relate to occurrence of HE. In atmospheric corrosion environments, steel corrosion proceeds with forming iron rust on the surface. The rust layer may affect hydrogen entry behavior into the steel. Therefore, it is needed to investigate the effect on rust layer on hydrogen entry behavior into steel. In this study, hydrogen entry behavior into steel exposed in an outdoor environment is discussed based on the results of hydrogen permeation current and corrosion potential. Experimental Hydrogen permeation current for steel exposed in an outdoor environment was measured by Devanathan-Stachurski method1. A sheet of plain carbon steel (0.020%C, 0.01%Si, 0.18%Mn, 0.015%P, 0.007%S, bal. Fe) was used as a material. The steel sheet was exposed at Choshi exposure test and research center (Chiba, Japan). The exposure test started at August, 2016 and the exposure period was changed from 1 to 6 months. After the exposure test, the steel sheet was cut into a small coupon of 25 mmw x 25 mml x 0.8 mmt. The exposed steel surface was washed with Milli-Q water (18 MΩ•cm). One side of the steel surface facing to the air was used as a hydrogen-entry side and the opposite surface of the steel was used as a hydrogen-withdrawal side for hydrogen permeation tests. The hydrogen-withdrawal side was polished and electroplated with Pd ca. 400 nm in thickness before hydrogen permeation test. A 30 μL of Milli-Q water was placed on steel to measure hydrogen permeation current. During drying of the water droplet, corrosion potential for the steel was measured with a Kelvin probe simultaneously with hydrogen permeation current. Results and Discussion In this study, hydrogen entry into steel exposed in an outdoor environment was investigated with hydrogen permeation current and corrosion potential measurements. It was found from the results of hydrogen permeation current and corrosion potential that hydrogen entry into steel after the exposure test was observed during drying of a water droplet. Therefore, hydrogen absorption reaction into the exposed steels occurs with corrosion. Figure shows change of the amount of hydrogen entry for the exposed steels in the test environment. The amount of absorbed hydrogen into steel was calculated by time-integral of hydrogen permeation current during drying of the water droplet. The plots at 0 month are obtained from the hydrogen permeation data for a bare steel. As shown in the figure, the amount of hydrogen entry into the exposed steel decreases significantly after one-month exposure and then it keeps almost constant independent of exposure period. After one-month exposure, the steel surface was wholly covered with iron rust. These results indicate that the formation of iron rust affected the amount of hydrogen entry into steel. Reference M. A.V. Devanathan, A. Stachurski, Proc. Roy. Soc., A270, 910 (1962). Figure 1