Effect of tensile stress on the hydrogen permeation of MS X65 pipeline steel under sulfide films

The effect of the tensile stress on the hydrogen permeation of MS X65 pipeline with sulfide films was investigated through measuring the steady-state hydrogen permeation current (I_∞), permeability (J_∞L) and apparent diffusivity (D_app) and quantitatively analysing the hydrogen-permeable resistance factor (HPRF) of single tensile stress HPRF (stress), single sulfide film HPRF (film) and the two together HPRF (stress-film). The results indicated that J_∞L and sub-surface hydrogen concentration (c_o) greatly increase and that D_app decreases as the elastic stress increases. When applying plastic stress, J_∞L and D_app all reduce, while c_o continues to increase without the film but decreases with the film. While single tensile stress can promote hydrogen permeation, with the sulfide film, the value of HPRE (stress-film) is not a simple addition of the value of the HPRE (stress) and the HPRE (film), and the interaction results in the blocking effect of hydrogen permeation. The surface morphology of the sulfide films changes caused by tensile stress should be responsible for the HPRE (stress-film) reducing as tensile stress increases but increasing with plastic tensile stress.     

Effect of tensile stress on the hydrogen adsorption of X70 pipeline steel

The effect of stress on the cathodic hydrogen evolution behavior of X70 pipeline steel was investigated by electrochemical tests, tensile tests, and microstructural characterization. The results indicated that the tensile stress enhanced the activity of hydrogen adsorption sites on the metal surface, which was considered as the dominating factor a?ecting generation, adsorption, and permeation of hydrogen atoms. The subsurface hydrogen atom concentrations quantified by Cyclic voltammetry (CV) tests and the data calculated by hydrogen permeation experiments showed a good correspondence. The results indicated that the tensile stress enhanced the adsorption of hydrogen atoms on the surface and an inhibitory effect on the Tafel and Heyrovsky reaction, thereby leading to the increase of the subsurface hydrogen atom concentration, enhance the hydrogen embrittlement susceptibility of the X70 steel material as demonstrated by plasticity loss in the tensile tests.     

Effects of surface oxide films on hydrogen permeation and susceptibility to embrittlement of X80 steel under hydrogen atmosphere

Hydrogen embrittlement (HE) induced by hydrogen permeation is a serious threat to the hydrogen transmission pipeline. In this study, oxide films were prepared on X80 steel by applying high-temperature oxidation, blackening treatment and passivation in concentrated H₂SO₄, and their effects on hydrogen permeation and HE susceptibility of X80 substrate were studied by conducting hydrogen permeation tests and slow strain rate tension (SSRT) tests. A numerical diffusion model was established to quantitatively determine the resistance of these oxide films to hydrogen permeation. Results showed that the oxide film prepared by high-temperature oxidation presented the highest resistance to hydrogen permeation with the ?_m/?_f value of 3828, and the corresponding HE index decreased from 38.07% for bare X80 steel to only 4.00% for that covered with oxide film. The characteristic of the corresponding fracture surfaces changed from brittle features such as quasi cleavage facets and secondary cracks to typical ductile dimple feature.     

Mathematical modeling,numerical simulation and experimental comparison of the desorption process in a metal hydride hydrogen storage system

A two-dimensional axisymmetric model is developed to study the hydrogen desorption reaction and its subsequent discharge in a metal hydride canister. Experimental tests are performed on an in-house fabricated setup. An extensive study on the effects of the metal properties and boundary conditions on discharging performance is carried out through non-destructive testing (NDT). Results show that the desorption process is more effective if the activation energy for desorption (E_d) and the reaction enthalpy (ΔH) decrease, and when the desorption rate coefficient (C_d) and the external convection heat transfer coefficient when the bottle is being heated (h) increase. Furthermore, porosity (ε) can be useful for the design of hydrogen storage systems, with a trade-off between charge/discharge time and storage capacity. Numerical and experimental results are compared achieving a good agreement. These results can be used to select metal hydride materials and also for the future evaluation of metal hydride degradation.     

Alloying effects of Ru and W on hydrogen diffusivity during hydrogen permeation through Nb-based hydrogen permeable membranes

The hydrogen permeability have been measured for pure niobium and Nb-5 mol%X (X = Ru and W) alloys in order to investigate the alloying effects of ruthenium and tungsten on the hydrogen diffusivity during hydrogen permeation. The hydrogen diffusion coefficient during hydrogen permeation is estimated from a linear relationship between the normalized hydrogen flux, J·d, and the difference of hydrogen concentration, ΔC, between the inlet and the outlet sides of the membrane. It is found that the addition of ruthenium or tungsten into niobium increases the hydrogen diffusion coefficient during the hydrogen permeation. On the other hand, the activation energy for hydrogen diffusion in pure niobium under the practical permeation condition is much higher than the reported values measured for dilute hydrogen solid solutions. It is interesting that the activation energy for hydrogen diffusion is decreased by alloying of ruthenium or tungsten into niobium.     

Study of the plasma and heating effect on hydrogen permeation through Pd0.60-Cu0.40 membrane in a micro-channel plate reactor

The diffusion of hydrogen through palladium and palladium-copper alloys membrane have been provided the highest hydrogen selectivity and permeance. In this study the composite Pd_0.60-Cu_0.40 wt% membrane foil with thickness 20 μm was measured in the micro-channel plate reactor (MPR) with gap length 4.5 mm. The hydrogen permeation flux was measured at atmospheric feeding pressure for 100% H₂ concentration in the temperatures range of 423–573 K under heating only and plasma-heating experiments. The plasma firing high voltage source ranges of 10–18 kV are tested. The hydrogen permeation flux and hydrogen permeability have been calculated according to Fick's and Sieverts combining laws with power exponent n-value 0.5. It was found that the maximum hydrogen flux, hydrogen permeability and Permeation rate percent of the heating only experiment at MPR heating temperature of 573 K and flow rate 0.1 l/min. In the plasma heating experiment, it was observed that the maximum hydrogen flux, hydrogen permeability, and permeation rate percent at MPR heating temperature of 573 K and plasma firing voltage of 14 kV. Also, the hydrogen permeation rate percent decreased due to the hydrogen reverse reaction even though the plasma firing voltage increased to 16 kV and 18 kV. The results also reveal that the activation energy and Pre-exponential constant factor decreased with increasing the feeding H₂ flow rate while the linear regression R² decreased with increasing H₂ feeding flow rate that in the heating only experiment, in contrast, the plasma-heating experiment showed non-linearity values. A comparison between both experiments showed the hydrogen permeation flux of the plasma-heating experiment is higher than that obtained from the heating only experiment, additionally; the plasma effect increased at low hydrogen flow rates. In contrast, the energy efficiency of heating only experiment was higher than that obtained from the plasma-heating experiment due to the total energy consumption of plasma experiment is high.     

Reversible hydrogen absorption in sodium intercalated fullerenes

The hydrogen absorption of sodium intercalated fullerenes (Na_xC₆₀) was determined and compared to pure fullerenes (C₆₀). Up to 3.5 mass% hydrogen can reversibly be absorbed in Na_xC₆₀ at 200 °C and a hydrogen pressure of 200 bar. The absorbed amount of hydrogen is significantly higher than for the case when only the sodium would be hydrogenated (∼1 mass% for x = 10). At 200 bar the onset of hydrogen absorption is observed at 150 °C. At a pressure of 1 bar hydrogen the major desorption starts at 250 °C and is completed at 300 °C (heating rate 1 °C min⁻¹). This absorption and desorption temperatures are significantly reduced compared to pure C₆₀, either due to a catalytic reaction of hydrogen on sodium or due to the negatively charged C₆₀. The hydrogen ab/desorption is accompanied by a partial de/reintercalation of sodium. A minor part of the hydrogen is ionically bonded in NaH and the major part is covalently bonded in C₆₀H_x. The sample can be fully dehydrogenated and no NaH is left after desorption. In contrast to C₆₀, where the fullerene cages for high hydrogen loadings are destroyed during the sorption process, the Na_xC₆₀ sample stays intact. The samples were investigated by X-ray, in-situ neutron powder diffraction and infrared spectroscopy. Na_xC₆₀ was synthesized by reacting sodium azide (NaN₃) with C₆₀ (molar ratio of Na:C₆₀ is 10:1).     

Improvement of desorption performance of Mg(BH4)2 by two-dimensional Ti3C2 MXene addition

Magnesium borohydride (Mg(BH₄)₂) is an attractive materials for solid-state hydrogen storage due to its high hydrogen content (14.9 wt%). In the present work, the dehydrogenation performance of Mg(BH₄)₂ by adding different amounts (10, 20, 40, 60 wt%) of two-dimensional layered Ti₃C₂ MXene is studied. The Mg(BH₄)₂-40 wt% Ti₃C₂ composite releases 7.5 wt% hydrogen at 260 °C, whereas the pristine Mg(BH₄)₂ only releases 2.9 wt% hydrogen under identical conditions, and the onset desorption temperature decreases from 210 °C to a relative lower temperature of 82 °C. The special layered structure of Ti₃C₂ MXene and fluorine plays an important role in dehydrogenation process especially at temperatures below 200 °C. The main dehydrogenation reaction is divided into two steps, and activation energy of the Mg(BH₄)₂-40 wt% Ti₃C₂ composite is 151.3 kJ mol⁻¹ and 178.0 kJ mol⁻¹, respectively, which is much lower than that of pure Mg(BH₄)₂.     

Insight into the mechanism of hydrogen permeation inhibition by cerium during electroplating: Enhanced kinetics of hydrogen desorption

In our previous work, we found that hydrogen permeation can be noticeably reduced during Ni–Cu electroplating by the addition of Ce salt to the plating solution. The mechanism of hydrogen permeation inhibition via Ce salt was further studied in the present work. Through the Iver–Pickering–Zamenzadeh (IPZ) model fitting of the kinetic of hydrogen evolution reaction, we found that the trace Ce salt that precipitated during electroplating could improve Tafel reaction kinetic parameters and reduce the strength of the Ni–H and Cu–H bonds due to its abundant d/f electrons and enough d/f orbitals. Meanwhile, Ce can provide electrons for the Heyrovsky reaction. These effects promoted surface electron migration and thus led to the desorption of adsorbed hydrogen atoms (H_ads) and the decreased diffusion of H_ads into the Ni–Cu coatings. The accuracy of the IPZ model fitting results was verified by hydrogen evolution rate experiments during the electroplating process. Hence, Ce salt can effectively inhibit hydrogen permeation and reduce the dehydrogenation annealing time, thereby showing great potential for energy saving and emission reduction in the electroplating industry.     

Effects of stress concentration on the mechanical properties of X70 in high-pressure hydrogen-containing gas mixtures

This study aims to investigate the mechanical properties of X70 pipeline steel under the synergistic influence of hydrogen and stress concentration. Slow strain rate tensile tests and low-cycle fatigue tests were performed on the specimens with different stress concentration factors (Kt) in 10 MPa nitrogen/hydrogen mixtures. Results show that the degradation degree of the ductility and fatigue life of X70 steel induced by hydrogen increases with the increase of Kt, and as the hydrogen partial pressure in mixtures increases, the influence of Kt on hydrogen-induced degradation increases as well. In addition, finite element analysis was performed via a modified hydrogen diffusion/plasticity coupled model to study the effect of Kt on hydrogen distribution in the specimens, which can influence the mechanical properties of X70. The maximum hydrogen concentration consistently appears at the notch tip of the specimen and increases with the increase of Kt, which is proposed to be one of the reasons for the severe hydrogen embrittlement of the specimens with large Kt. As the axial tensile force on the specimen increases, the maximum hydrogen concentration at the notch tip begins to be dominated by hydrogen in the normal interstitial lattice sites and, subsequently, in the trapping sites.     

Analysis of hydrogen diffusion coefficient during hydrogen permeation through pure niobium

The hydrogen solubility and the hydrogen permeability of pure niobium at high temperature are investigated in order to analyze the hydrogen diffusion coefficient during the hydrogen permeation. It is shown that the hydrogen dissolution reaction into niobium metal does not follow the Sieverts' law at the practical hydrogen permeation pressures. The hydrogen diffusion coefficient during the hydrogen permeation through pure niobium at high temperature is evaluated from the linear relationship between the normalized hydrogen flux, J·d, and the hydrogen concentration difference, ΔC. It is found that the hydrogen diffusion coefficient under the practical condition is much lower than the reported values measured for dilute hydrogen solid solutions. Surprisingly, the hydrogen diffusion is found to be faster in Pd–Ag alloy with fcc crystal structure than in pure niobium with bcc crystal structure at 773 K during the hydrogen permeation.     

Exergy and energy analysis of hydrogen production by the degradation of sodium borohydride in the presence of novel Ru based catalyst

Chemically possible hydrogen storage material of the most important and widely used metal hydride compound is sodium borohydride. A current research issue is the development of systems that allow regulated hydrogen generation employing appropriate catalysts for the creation of hydrogen gas from the hydrolysis of sodium borohydride (NaBH₄). In this study, controlled hydrogen production from alkali solution of NaBH₄ was aimed. On hydrogen generation rate (HGR), the effects of NaBH₄ and alkaline solution concentrations, catalyst quantity, and temperature were examined. Considering the energy and exergy analysis, which have gained importance in the international arena in recent years, in this study, the exergy energy analysis of the environment in which the sodium borohydride solution is located was performed. The best one of the Ru-based catalysts synthesized in different atomic ratios was determined as 90:10 RuCr. The surface characterization of the obtained catalyst was carried out using scanning electron microscope (SEM-EDX) and X-ray diffractometer (XRD). In the kinetic calculations, the activation energy was calculated as 35,024 kj/mol and the reaction ordered n was found to be 0,65. By applying exergy and energy analysis to the hydrogen production step, the energy and exergy efficiency of the system were found to be 24% and 7%, respectively.     

Hydrogen permeation behavior of X70 pipeline steel simultaneously affected by tensile stress and sulfate-reducing bacteria

The hydrogen permeation behavior of submarine pipelines buried in anoxic sea mud and protected by cathodic potential is affected by both sulfate-reducing bacteria (SRB) and tensile stress. In this study, the individual and simultaneous effects of SRB and tensile stress on hydrogen permeation parameters were investigated using an electrochemical hydrogen permeation method together with mechanical tensile tests. Cathodic potentiodynamic polarization and surface morphology investigations were also conducted. Both elastic and plastic stresses were considered. Results showed that SRB enhanced the sub-surface hydrogen concentration significantly but had little influence on the diffusion coefficient. Elastic stress had a minimal effect on the hydrogen permeation behavior of X70 steel. Plastic stress reduced the diffusion coefficient and increased the sub-surface hydrogen concentration. The lattice trap produced by plastic deformation was responsible for the impact of plastic stress on hydrogen permeation. SRB and plastic stress not only enhanced the sub-surface hydrogen concentration independently, but also had synergistic effects accelerating the hydrogen accumulation on a steel surface.     

Oxygen permeability and stability of dual-phase Ce0.85Pr0.15O2-δ-Pr0.6Sr0.4Fe0.9Al0.1O3-δ membrane for hydrogen production by water splitting

A series of dense xCe_0.85Pr_0.15O_2-δ (CP) -(100-x) Pr_0.6Sr_0·4Fe_0·9Al_0·1O_3-δ (PSFA) (x = 30, 40, 50, 60, 70) dual-phase oxygen transport membranes were successfully synthesized by sol-gel method. The feasibility of xCP-(100-x) PSFA membranes for hydrogen production by thermochemical water splitting was explored by testing in the thermochemical stability, oxygen permeability, hydrogen production efficiency, and performance degradation mechanism of these membranes. The results show that the thermochemical stability of xCP-(100-x) PSFA membranes is improved with the CP content increasing. The oxygen permeation model demonstrates that appropriate CP content is beneficial to reduce the permeation resistance of xCP-(100-x) PSFA membranes, and the reaction of surface exchange plays a major role in the oxygen transport process at 925 °C. The formation of Fe(SiO₃) and Sr₃Fe₂O₇ on the sweep side leads to the decline in hydrogen production rate. The 60CP-40PSFA membrane showed the best comprehensive performance with a hydrogen production retention rate of 90% and a stable hydrogen production rate of 0.99 ml cm^?2 min^?1 in the 100-h test cycle.     

Hydrogen diffusion and hydrogen influenced critical stress intensity in an API X70 pipeline steel welded joint – Experiments and FE simulations

An API X70 pipeline steel has been investigated with respect to hydrogen diffusion and fracture mechanics properties. A finite element cohesive element approach has been applied to simulate the onset of hydrogen-induced fracture. Base metal, weld simulated heat affected zone and weld metal have been investigated. The electrochemical permeation technique was used to study hydrogen diffusion properties, while in situ fracture mechanics testing was performed in order to establish the hydrogen influenced threshold stress intensity. The average effective diffusion coefficient at room temperature was 7.60 × 10⁻¹¹ m²/s for the base metal, 4.01 × 10⁻¹¹ m²/s for weld metal and 1.26 × 10⁻¹¹ m²/s for the weld simulated heat affected zone. Hydrogen susceptibility was proved to be pronounced for the heat affected zone samples. Fracture toughness samples failed at a net section stress level of 0.65 times the yield strength; whereas the base metal samples did not fail at net section stresses lower than the ultimate tensile strength. The initial cohesive parameters which best fitted the experimental results were σ_c = 1500 MPa (3.1·σ_y) for the base metal, σ_c = 1800 MPa (3.0·σ_y) for weld metal and σ_c = 1840 MPa (2.3·σ_y) for heat affected zone. Threshold stress intensities K_Ic,HE were in the range 143–149 MPa√m.     

Effect of nickel on hydrogen permeation in ferritic/pearlitic low alloy steels

Nickel offers several beneficial effects as an alloying element to low alloy steels. However, it is, in the oil and gas industry, limited by part 2 of the ISO 15156 standard to a maximum of 1 wt% due to sulfide stress cracking resistance concerns.Hydrogen uptake, diffusion, and trapping were investigated in research-grade ferritic/pearlitic low alloy steels with Ni contents of 0, 1, 2 and 3 wt% by the electrochemical permeation method as a function of temperature and hydrogen charging conditions.Qualitatively, the effective diffusion coefficient, D_eff, decreased with increasing Ni content. The sub-surface lattice hydrogen concentration, C₀, decreased with increasing Ni content in all charging conditions while the trend between the sub-surface hydrogen concentration in lattice and reversible trap sites, C_OR, and Ni content varied with the charging conditions. Irreversible trapping, evaluated by consecutive charging transients, was not observed for any of the materials. Lastly, the possible influence of an increasing fraction of pearlite with increasing Ni content is discussed.     

Electrochemical determination of niobium cathode as an efficient electrocatalyst for hydrogen generation in acidic media

Hydrogen gas (H₂) is notified as a renewable energy carrier. It is wanted to discover a low-cost electrocatalyst for the hydrogen evolution reaction (HER) to substitute the high-cost Pt in electrolysis cell. Niobium electrocatalyst nominated to substitute noble materials for electrocatalytic H₂ production and its electrochemical manner was estimated in H₂SO₄ acid of various concentrations utilizing a steady-state polarization and electrochemical impedance spectroscopy (EIS). The influences of acid concentration, cathodic potential and temperature on the H₂ creation were examined. The outcomes display that HER on Nb electrode proceeds by the Volmer-Heyrovsky mechanism. EIS tests, under open circuit and under cathodic polarization, were performed and the fitting has been done utilizing a suggested model for the electrode/electrolyte interface. Apparent activation energies (E_a) were estimated to be ca. 10.5 kJ mol^?1 for the HER on Nb. Thus, Nb is a good electrocatalyst for the cathodic H₂ manufacturing.     

Catalyst-free low temperature conversion of n-dodecane for co-generation of COx-free hydrogen and C2 hydrocarbons using a gliding arc plasma

In this study, plasma reforming of n-dodecane for the co-generation of CO_x-free hydrogen and C₂ hydrocarbons at low temperature and ambient pressure has been investigated in a gliding arc discharge (GAD) reactor. The selective synthesis of H₂, C₂H₂ and C₂H₄ and the energy efficiency for n-dodecane conversion can be tuned by changing different processing parameters including the gas flow rate, n-dodecane concentration and input voltage. The highest selectivities of H₂ (76.7%), C₂H₂ (41.4%) and C₂H₄ (12.0%) were achieved with an n-dodecane conversion of 68.1%. The generation of mixed hydrogen, acetylene and ethylene offers the possibility for in-situ hydrogenation to enhance the selectivity of light olefins (e.g., ethylene) without prior gas separation. The plausible reaction mechanism and pathways in the plasma cracking of n-dodecane have been discussed through plasma emission spectroscopic diagnostics coupled with a comprehensive analysis of gas and liquid products. A strong correlation between the yield of C₂ hydrocarbons and the relative intensity of C₂ Swan bands was found, which suggests that C₂ Swan bands could be used as a valuable probe to understand the generation of C₂ hydrocarbons in the plasma reforming of hydrocarbon oils.     

Investigation of hydrogen generation from sodium borohydride using different cobalt catalysts

Effective Co/Cu, CoB/Cu, and CoBM (M = Mo,Zn,Fe)/Cu catalysts were prepared on the copper surface by a simple electroless deposition method using a morpholine borane as a reducing agent in the glycine solution. The activity of the deposited catalysts was investigated for hydrogen generation from an alkaline sodium borohydride solution. It was determined that these synthesized catalysts demonstrated the catalytic activity for the hydrolysis reaction of NaBH₄. The lowest obtained activation energy (E_A) of the hydrolysis reaction of NaBH₄was 27 kJ mol^?1 for the CoBMo/Cu catalyst. The hydrogen generation rate of 15.30 ml min^?1 was achieved using CoBMo/Cu catalysts at 313 K and it increased ~3.5 times with the increase of temperature to 343 K. The highest hydrogen generation rate obtained by CoBMo/Cu films may be related to the hierarchical cauliflower-shaped 3D structures and the high roughness surface area. Moreover, the CoBMo/Cu catalyst showed an excellent reusability.     

Hydrogen adsorption on Li decorated graphyne-like carbon nanosheet: A density functional theory study

Motivated by novel graphyne-like carbon nanostructure C₆₈-GY, spin-polarized DFT calculations with dispersion-correction were performed to investigate the hydrogen adsorption capacity of Li decorated C₆₈-GY nanosheet. The binding energy between Li and C₆₈-GY was larger than the cohesive energy of bulk metal, indicating Li atoms would prefer to separately attached on C₆₈-GY. The ab initio molecular dynamics simulation has been performed to confirm the stability of Li/C complex. When five Li atoms decorated on C₆₈-GY, 14H₂ molecules were captured. The maximum hydrogen storage density was 8.04 wt% with an average hydrogen adsorption energy of −0.227 eV per H₂. The positively charged Li atoms aroused electrostatic field and induced the polarization of H₂. It was notable to observe strong hybridization between the main peak of H-1s orbitals with Li below Fermi level, which was responsible for the enhancement of hydrogen binding energy, indicating its potential application on hydrogen storage.