Increasing Hydrogen Content Research Articles

Optimization of membrane thickness for proton exchange membrane electrolyzer considering hydrogen production efficiency and hydrogen permeation phenomenon

Reducing the membrane thickness of Proton exchange membrane (PEM) electrolyzer was found to efficiently promote the hydrogen production rate. However, it can also aggravate the phenomenon of hydrogen permeation, leading to an increased hydrogen content on the anode side and posing a risk of explosions. Thus, optimal design of the membrane thickness of PEM electrolyzer systems is crucial to ensure both safe and efficient hydrogen production. In this paper, we propose two optimization problems for the membrane thicknesses, aiming at achieving a balance between the hydrogen content on the anode side and the hydrogen production rate under constant and varying power input conditions. First, the theoretical model of a PEM electrolyzer is established, and a photovoltaic-PEM electrolyzer system is considered to provide varying power input conditions. Then, the two optimization problems are formulated and resolved using the sequential quadratic programming (SQP) and particle swarm optimization (PSO) algorithms, respectively. Our results reveal that the optimal membrane thickness decreases as the constant input power increases. This suggests that high/low power inputs require thin/thick membranes. For varying power input, we collected one year of solar radiation intensity data from four different regions in China. The findings demonstrate that the selection of the optimal membrane thickness depends not only on the average solar radiation intensity but also on its seasonal variations. By applying these strategies, we effectively optimize the membrane thickness in PEM electrolyzer systems, thereby enhancing the efficiency and safety of hydrogen production. The outcomes provide valuable insights for selecting the appropriate membrane thickness in regions with varying solar radiation intensities and accounting for seasonal variations in solar radiation.

The investigation on exploring rare earth hydrides superconductors

This review provides a comprehensive overview of the challenges and potential solutions in the quest for high-temperature superconductivity using hydrogen-rich materials. Traditional superconductors often face limitations in terms of critical transition temperatures (Tc) and stability under high pressures. However, hydrogen-rich compounds offer promising avenues due to their strong electron-phonon coupling, elevated Debye temperatures, and high electronic density. Recent discoveries, such as H3S, have further invigorated the field. While an excess of H2-like units can adversely affect Tc, clathrate structures like CaH6 and YH6 present viable alternatives by fostering high symmetry. Rare earth hydrides, notable for their electron-donating capabilities, have undergone extensive testing. Isotope effect studies, as exemplified by LaH10 and LaD10, highlight the critical role of hydrogen vibrations in superconductivity. Ternary superhydrides incorporating dopant elements aim to reduce the pressure requirements for stability, with LaBeH8 emerging as a promising candidate, exhibiting a Tc of 110 K at 80 GPa. The review concludes by outlining future research directions, such as the incorporation of small-radius atoms to increase hydrogen content, a deeper understanding of the role of symmetry, and addressing challenges related to vibrational modes and structural stability.

Quantitative analysis of local plasticity accompanying hydrogen-related fracture in low-carbon martensitic steel

In this study, the local plasticity accompanying hydrogen-related fracture in a low-carbon martensitic steel was quantitatively investigated by correlative microscopy analysis combining digital image correlation technique and electron backscatter diffraction. The results revealed that strain localization occurred mainly in the bulk of martensite blocks and at prior austenite grain boundaries, both with and without the presence of hydrogen. Moreover, hydrogen enhanced strain localization during deformation and facilitated crack nucleation and propagation. The quantitative analysis showed that the hydrogen-related quasi-cleavage cracking was closely related to the local plastic deformation, and increasing hydrogen content decreased the local strain level required for quasi-cleavage cracking. It was found that strain localization also occurred around the intergranular cracks, suggesting that hydrogen-induced intergranular cracking was not a classical simple decohesion process and strain localization was involved in the sequence of hydrogen-induced intergranular cracking. These findings shed light on the understanding of the intrinsic nature of hydrogen embrittlement.

Hydrogen embrittlement behavior of two mining chain steels by slow strain rate test

Two mining chain steels 23MnNiMoCr5-4 and 0.3C0.2Si0.3Mn4.2(Cr+Ni+Mo) with tensile strengths of 1200 MPa and 1250 MPa, respectively, were employed to investigate their hydrogen embrittlement behaviors by slow strain rate tests combined with thermal desorption analyses. It is shown that at initial stage the fracture stress decreases linearly as the hydrogen content increases, and the turning points occur at hydrogen content of 1.2 wppm for 0.3C0.2Si0.3Mn4.2(Cr+Ni+Mo) and 0.26 wppm for 23MnNiMoCr5-4. The fractured surface observation suggests that the ratio of intergranular fracture area to quasi-cleavage area increases dramatically at the turning points. The maximum hydrogen contents resulting from the corrosive HCl solutions with pHs of 2 are approximately 0.6 wppm 0.3C0.2Si0.3Mn4.2(Cr+Ni+Mo) and 0.11 wppm for 23MnNiMoCr5-4, corresponding to the activation energies for hydrogen desorption are 21.57 kJ/mol and 14.53 kJ/mol, respectively.

Hydrogen storage of high entropy alloy NbTiVZr and its effect on mechanical properties: A first-principles study

In recent years, high entropy alloys (HEAs) have demonstrated remarkable potential for hydrogen storage applications. Although extensive experimental studies have been conducted, a detailed understanding of the hydrogenation process at the atomic level is still lacking. In this study, first-principles calculations were employed to explore the microstructural evolution during hydrogen absorption in NbTiVZr as well as the mechanical characteristics of hydrides. The results indicate that a phase transition from BCC to FCC occurs in the hydride when the hydrogen content reaches 0.05 wt%. Hydrogen tends to occupy the octahedral interstitial sites in the BCC hydrides, while the preferred hydrogen sites in FCC hydrides undergo a transition from octahedral sites → tetrahedral + octahedra sites → tetrahedral sites as the hydrogen content increases. The highest hydrogen storage capacity of NbTiVZr was predicted by the phonon spectra of hydrides to be 2.94 wt%. Vanadium (V) is discovered to play a crucial role in hydrogen absorption capacity by causing significant lattice distortion and forming stronger bonds with hydrogen. Additionally, all hydrides exhibit great mechanical properties and thermal stability. Our research reveals that NbTiVZr has an excellent capacity for storing hydrogen and has the potential for applications in hydrogen storage materials.

Flame evolution and pressure dynamics of methane-hydrogen-air explosion in a horizontal rectangular duct

This work is aimed at exploring flame evolution and pressure dynamics of methane-hydrogen-air explosion experimentally and numerically by changing equivalence ratio and hydrogen content. For the flame evolution, the smooth distortion vanishes at equivalence ratio of Ф = 1.4, the prominent cellular structure and distorted tulip flame start to form with increasing hydrogen content. For the pressure dynamics, as the equivalence ratio increases, both maximum explosion overpressure and maximum pressure rise rate increase and then decrease, and both of them continue to increase with increasing hydrogen content. H + O2 = O + OH is the main elementary reaction with positive effect on the laminar burning velocity. The main elementary reactions with negative effects are H + O2(+M) = HO2(+M) and CH3 + H(+M) = CH4(+M). H radical always dominates on the rich side or the lean, stoichiometric side with high hydrogen content. As the hydrogen content increases, the main oxidation pathways of CH4 undergoes the transfer from CH4 → CH2(S) → CH2 → CO to CH4 → CH2(S) → CH2 → CH → CO → CO2. The research results are helpful to improve combustion efficiency of internal combustion engine and ensure process safety of hydrogen doped natural gas pipeline transportation.

Experimental study on jet fire characteristics of hydrogen-blended natural gas

Blending hydrogen into natural gas can increase fuel reactivity and the risk of jet fires in case of pipeline leakage though it is an effective delivery method. In this work, horizontal jet fires of hydrogen-blended natural gas at various operating pressures and hydrogen content were investigated experimentally. The flame temperature, lift-off distance, and flame length were measured for the scenarios with 0%–50% hydrogen content (in volume fraction) and 200–800 Pa. Results show that with the increase of hydrogen content, the flame temperature rises while the lift-off distance and flame length decrease. The flame length is slightly affected when the hydrogen content is less than 10% and a maximum reduction in flame length is 13.7% as the blended hydrogen content increases to 50%. Further theoretical analysis suggested the dimensionless correlations of the temperature distribution along the jet axis, lift-off distance, and flame length with different hydrogen content, respectively. The research results may provide reference for the risk assessment of hydrogen-blended natural gas pipelines.

Study on flame propagation and inherent instability of hydrogen/ammonia/air mixture

To improve the safety and reliability of hydrogen energy, this paper studied the flame propagation and instability characteristics of hydrogen/ammonia/air mixture under different hydrogen contents, equivalence ratios and initial pressures. The results show that three typical phenomena are observed in the premixed hydrogen/ammonia/air flame propagation process under different experimental conditions. In a stable flame, the roughness of the flame surface does not increase, while during unstable flame expansion, the cracking of the flame surface splits and increases. In addition, under the condition of low equivalence ratio and hydrogen content, significant flame uplift is observed. With the increase in hydrogen content, the flame thickness and critical instability radius of the hydrogen/ammonia/air mixture decrease monotonously. The increase of hydrogen content mainly strengthens the hydrodynamic instability, leading to the weakening of flame stability. With the increase of the equivalence ratio, the Markstein length and the critical instability radius increase monotonically. The minimum value of flame thickness appears at the equivalence ratio of 1.0. The Lewis number is always less than 1 for poor combustion and greater than 1 for rich combustion. An increase in the hydrogen content only moves the Lewis number further away from 1. In rich burn, the thermal-diffusion is beneficial to flame stability, and the flame thickness increases with the increasing equivalence ratio. Under the combined effect of thermal-diffusion and hydrodynamic instability, the overall stability of the hydrogen/ammonia/air flame gradually increases with the increasing equivalence ratio. With the increase of initial pressure, the flame thickness decreases gradually. The critical instability radius and Markstein length both decrease rapidly with the increase of initial pressure.

Impact of Hydrogen in Ga‐Doped Silicon on Maximum LeTID Defect Density

Many studies suggest that hydrogen is an important factor for light and elevated temperature‐induced degradation (LeTID) in p‐type c‐Si solar cells. The exact mechanism of this defect is still unknown. Here, Ga‐doped Si wafers fired with an SiN x :H layer present were used to establish a correlation between the initial concentration of GaH pairs and H2 dimers on one and the maximum defect density evolving during degradation on the other hand. Degradation of all samples is performed at constant excess charge carrier injection. The correlation to LeTID defect density is found to be linear in the case of [H2], hence, a direct involvement of H2 in the defect formation is expected. In contrast, the correlation between GaH pairs and defects is found to scale with the fraction of GaH on total hydrogen concentration. This fraction is not constant but rather decreases with an increase in total hydrogen concentration. In addition, changes in [GaH] and lifetime are examined under different degradation conditions with either fixed injection up to and temperatures up to 180 °C. Under these conditions, LeTID evolves but no dissociation of [GaH] takes place. The effective activation energy of LeTID defect formation is determined to be 0.76(17) eV.

The effect of pipeline sudden contraction structure on the deflagration characteristics of hydrogen-methane-air

Based on the visualized gas cloud explosion pipeline test platform, the influence of the sudden contraction structure on the deflagration characteristics of the hydrogen-methane-air gas cloud is investigated. The results show that the changes of flame propagation velocity, explosion overpressure, and flame temperature after deflagration of the premixed gas cloud all present three stages: rapid increase, rapid decline, and secondary acceleration caused by the sudden contraction of pipeline structure. The equivalence ratio significantly affects the hydrogen-methane-air detonation process in the sudden contraction of the pipe structure. As the hydrogen content increases, the flame propagation becomes faster and the explosion impact becomes greater. The formation of “Tulip” flame is closely related to the flame propagation speed. During the process of flame propagation, inertia dominates, causing the flame propagation speed to reach its first peak at the abrupt contraction structure.

Characteristics of Explosion Hazards in Methane–Air Mixtures Diluted by Hydrogen

The combustion efficiency of methane can be effectively enhanced with the occurrence of hydrogen. However, the combustion characteristic of premixed methane/hydrogen/air is not fully understood. In this study, the effect of the amount of hydrogen addition on the explosion risk of premixed CH4/air combustion was fully investigated through experiments and simulations. The explosion overpressure of premixed CH4/air combustion with various hydrogen additions was measured in a standard 20 L spherical closed vessel. Meanwhile, the microscopic flame structures for the same cases were simulated using 2022 Chemkin-Pro software. The results showed that hydrogen could increase the explosion risks of premixed CH4/air combustion. The rate of key elementary reactions R38: H + O2 <=> O + OH and R84: OH + H2 <=> H + H2O in the system could be accelerated by hydrogen. The peak explosion overpressure in the closed chamber is boosted and the arrival time of peak overpressure rise rate is shortened, which raises the danger. Especially under lean and rich combustion conditions, hydrogen could potentially lead to more dangerous situations. With the increase in hydrogen concentration, the reaction rate of key elementary reactions accelerates faster, the peak explosion overpressure increases more, and the peak overpressure rise rate arrives earlier.

Magnetoresistance in Pd–Co/Cu/Pd–Co trilayer under hydrogen–nitrogen gas mixture

The magnetoresistance of three Pd–Co(1)/Cu/Pd–Co(3) trilayers with different Pd–Co(3) thicknesses were evaluated in a H2–N2 gas mixture. The resistance of Pd–Co/Cu/Pd–Co increased with increasing hydrogen concentration in the gas phase, which is similar to the behavior observed in the Pd metal. The peak structure was shown in the magnetoresistance under a nitrogen atmosphere and was associated with magnetic scattering at the interface between the Pd–Co and Cu layers. In the H2–N2 gas mixture, the peak position and width in the resistance profiles were independent of the hydrogen concentration for all the prepared trilayers, and the peak intensity decreased with increasing hydrogen concentration for the trilayer containing a 4.2 nm thick Pd–Co(3) layer. The decrease in intensity was due to the reduction in magnetization in the Pd–Co layer after hydrogen absorption. The change in the resistance ratio by hydrogen absorption in the trilayer was larger under a high external magnetic field of 170 mT than under a low magnetic field of 10 mT. These results confirmed that the multilayered structure of the Pd–Co/Cu enhances the resistance response to hydrogen under a high magnetic field.

The Reduction Step and Mechanism Analysis of the NiO-8YSZ Anode Affected by the Hydrogen Concentration

The reduction of the NiO-YSZ anode has a direct bearing on the performance of the solid oxide fuel cell, and the hydrogen concentration is a significant condition during the reduction process. Hydrogen at different concentrations were used to reduce the NiO-YSZ anode and the initial performances of the solid oxide fuel cells were tested to reveal the influence of the hydrogen concentration on the reduction of the NiO-YSZ anode. The experimental results suggested that four stages of the open circuit voltage exist during the reduction of the NiO-YSZ anode, namely rapid increase period, temporary stasis period, slow increase period and final stable period successively. The rates of the rapid increase period and the slow growth period showed significant positive correlations with the hydrogen concentration of the reduction while there was a negative correlation between the duration of the temporary stasis period and the hydrogen concentration of the reduction. The values of the temporary stasis period were 0.83V approximately, which were irrelevant to the hydrogen concentration of the reduction. During the final stable period, the variation of the open circuit voltage is less than 1mV/h, which were close to the theoretical open circuit voltage. After the reduction of the NiO-YSZ anode, the ohmic resistance of the solid oxide fuel cell was about 0.31Ω /cm2 and did not reveal a clear correlation with the hydrogen concentration of the reduction. The polarization resistance showed significant negative correlation with the hydrogen concentration of the reduction on open circuit. But under the on-load condition, the same phenomenon only occurred in low hydrogen concentration of the reduction and then the polarization resistance remained largely the same with the increasing hydrogen concentration of the reduction. There was a direct correlation between the initial performances of the solid oxide fuel cell and the polarization resistance under the on-load condition that the initial performances can be improved with the increasing hydrogen concentration during the reduction process of the NiO-YSZ anode when the hydrogen concentration was low and then the initial performances remained constant basically with the continuing increasing hydrogen concentration. The abovementioned phenomena demonstrate that the resistance on open circuit represent nothing to the performances of the solid oxide fuel cell under the on-load condition. Previous researches about the NiO reduction by hydrogen, especially the shrinking core model can be used to explain the abovementioned phenomena. The reduction of the NiO is a volume reduction process. The reaction interface of the Ni/NiO moves inwards during the reduction, forming an unreacted NiO core surrounded by a rim of metallic Ni with much porous structures finally. The H2O produced in the reduction is absorbed onto the surface of the unreacted NiO core, improving the apparent activation energy and limiting diffusion of the Ni atoms to appropriate nucleation centers. Thus, the reduction process is retarded, forming the temporary stasis period. The absorbed H2O removes out through the porous structures of the rim of the metallic Ni. Meanwhile the H2 penetrates deeper and continues to reduce the unreacted NiO core, which is the mechanism of the slow increase period. According to the shrinking core model, higher hydrogen concentration can make the unreacted NiO core smaller, lessening the H2O absorbed onto the surface. Thus, the time needed for the absorbed H2O removal is shorten, leading the duration of the temporary stasis period showed significant negative correlation with the hydrogen concentration. The previous researches attribute the activation of the solid oxide fuel cell to the coarsening of the Ni particle or the further reduction of the unreacted NiO core. In this experiment, the performance of the solid oxide fuel cell with the NiO-YSZ anode reduced by 5% hydrogen concentration was lowest, and thus its potential of the activation was highest. In the first 20 hours of the operation, its performance kept improving and achieved that of the solid oxide fuel cells with the NiO-YSZ anodes reduced by higher hydrogen concentration. But the performance of the solid oxide fuel cells with the NiO-YSZ anodes reduced by higher hydrogen concentration did not significantly improve in the first 20 hours of the operation. The comparison showed that the cause of the activation of the solid oxide fuel cell is quite possible the further reduction of the unreacted NiO core.

Direct steam reforming of the product gas from ethanol gasification with supercritical water

A continuous process for producing hydrogen from the gasification of ethanol with supercritical water (SCWG) is investigated, which involves a fixed bed steam methane reforming (SMR) reactor downstream of the SCWG reactor. Increasing temperature and decreasing space velocity in the SMR reactor resulted in increased hydrogen concentration and methane conversion. The catalyst activity was more affected at low than high pressures, presumably due to the kinetics of the SMR reaction. The significant increase in total hydrogen yield based on ethanol in the feed showed the importance of installing the reformer after gasification. The excessive steam from the SCWG reactor helped to prevent carbon formation, but it might have resulted in the sintering of the active metal. A long-time experiment proved the stability of the catalyst up to 49 h of time on stream (TOS) with a minor decrease in methane conversion from 84% to 78%.

The influence of hydrogen on phase stability, mechanical and electronic properties of B2–ZrCu compound from first-principles

The influence of hydrogen doping on phase stability, mechanical and electronic properties of B2–ZrCu compound was systematically investigated by first-principles calculations. As hydrogen concentration increases, Zr–H bonds and Cu–H bonds makes the metallicity of the system decrease and covalency increase as shown by density of states and electron density difference distribution. Higher covalent character decreases formation enthalpy, which corresponds to better stability. Higher bond covalency also improves hardness and brittleness. However, the lattice structural symmetry and crystallographic packing density play a crucial role in affecting ductility, which make Zr8Cu8H2−<110> display a softer and more ductile character than non-doped Zr8Cu8. Otherwise, the hardness and embrittlement will increase monotonically with the increasement of interstitial hydrogen doping concentrations. The combination of covalency, crystalline symmetry and packing density of interstitial hydrogens play a crucial role in mechanical behavior; while the overall bonding character decides the stability.

Hydrogen storage properties of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 lightweight high entropy alloy: A theoretical study

In the past several years, Mg-based high entropy alloys (HEAs) have attracted great attention in high gravimetric hydrogen storage capacity. In this work, the hydrogen storage properties of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 HEA are investigated by first-principles calculations. With increasing hydrogen concentration, the structural stability of BCC and FCC hydrides decreases and increases, respectively. By comparing the lattice constants, number of hydrogenation-induced abnormal short hydrogen-hydrogen bonds and radial distribution functions of BCC and FCC hydrides, it is found that the hydrogen accommodation ability of BCC phase is weaker than that of FCC phase, and a BCC to FCC phase transformation occurs during hydrogenation process. Further total energy calculations suggest that the threshold hydrogen content of phase transformation for Mg0.10Ti0.30V0.25Zr0.10Nb0.25 is around H/M = 1.16. By phonon spectra calculation, the maximum gravimetric hydrogen storage capacity of Mg0.10Ti0.30V0.25Zr0.10Nb0.25 is predicated to be as high as 3.16 wt%, demonstrating that Mg0.10Ti0.30V0.25Zr0.10Nb0.25 HEA is a potential hydrogen storage material.

Combined influence of strain rate and hydrogen on the deformation behavior of a near-α titanium alloy

The deformation behavior of the near-α titanium alloy Ti–6Al–3Nb–2Zr–1Mo, containing 20–210 ppm hydrogen and tested at strain rates of 10−5–10−1 s−1, has been investigated by conducting tensile testing and microstructural characterization. The results show that at strain rates ≤10−3 s−1, increasing hydrogen concentration improves ductility, while it deteriorates ductility at higher strain rates. The change in ductility with increasing strain rate remains relatively small at strain rates ≤10−3 s−1 for all hydrogen concentrations, but at higher strain rates, an increase in strain rate results in a decrease in ductility. Additionally, the addition of hydrogen has little effect on the strain rate sensitivity and work hardening exponent. The detrimental effect of hydrogen addition on ductility at strain rates >10−3 s−1 can be attributed to the enhanced strain localization caused by the presence of hydrogen. In cases of lower strain rates, the increase of ductility with the addition of hydrogen is due to the promotion effect of hydrogen on dislocation mobility.

The hot deformation behavior and dynamic microstructure evolution of additive manufactured Ti6Al4V with different hydrogen addition

During the laser melting deposition (LMD) additive manufacturing process, titanium alloys undergo rapid solidification, which induce grain growth into coarse columnar grains, resulting in lower mechanical properties of the material than conventional forgings. This study proposes the incorporation of hydrogen into titanium alloys to refine columnar grains, reduce deformation resistance, and improve machinability. In this work, the hot deformation behavior of hydrogenated Ti6Al4V alloy was analyzed via high-temperature compression experiment. The experimental results revealed the nucleated grains generated by the intense deformation and the twins brought by the hydrogen element led to massive dynamic recrystallizations, which effectively improved the hot workability. When the alloys are deformed above phase transition temperature, the flow stress is positive related with H content. Meanwhile, when the alloys are deformed below the phase transition temperature, the flow stress initially experiences a decrease with an increase in hydrogen content. Adding only 0.27 wt% H can reduce the flow stress by 34.4%–54%, but when the H content continues to increase, the flow stress still increases subsequently. Moreover, when the strain rate is constant, the flow stress of Ti6Al4V alloy can decrease by about 80% with an increase in deformation temperature from 820 °C to 940 °C. When the deformation temperature is constant, the flow stress of Ti6Al4V alloy with different hydrogen contents can decrease by around 65% as the strain rate reduces from 10s−1 to 0.01 s−1.

Evolution of ammonia reaction mechanisms and modeling parameters: A review

Ammonia (NH3) has been suggested as a fuel to attain zero carbon emissions. However, dealing with ammonia needs careful studies to reveal its limits as a suitable and promising fuel for broad applications within large power requirements. Chemical reaction mechanisms, widely employed in the modeling of these applications, are still under development. Therefore, this review is aimed to shed light on the current mechanisms available in the literature, highlighting modeling parameters that directly affect reaction rates which in turn govern the performance of each reaction mechanism. The key findings denote that most of the reaction mechanisms have poor performance when predicting combustion characteristics of ammonia flames such as laminar flame speed, ignition delay time, and nitrogen oxide emissions (NOx). In addition, none of the mechanisms have been optimised efficiently to predict properly experimental measurements for all these combustion characteristics. For example, Duynslaegher's mechanism perfectly predicted the laminar flame speed at lean and stoichiometric conditions, while Nakamura's reaction mechanism worked properly at rich conditions for the estimation of laminar flame speed. Although the aforementioned mechanisms achieved good estimation in terms of laminar flame speed, they showed poor performance against NO mole fractions. Similarly, Glarborg's (2018) mechanism properly estimated NO mole fractions at lean and stoichiometric flames while Wang's mechanism performed well in rich conditions for such emissions. Other examples are presented in this manuscript. Finally, the prediction performance of the assessed mechanisms varies based on operating conditions, mixing ratios, and equivalence ratios. Most mechanisms dealing with blended NH3 combinations gave good predictions when the concentration of hydrogen was low, while deteriorating with increasing hydrogen concentrations; a result of the shift in reactions that require more research.

Effect of water salinity on properties of multipass underwater wet manual metal arc welded joints

The weldability of steel under the water is limited due to the influence of the environment. Water causes limited visibility, presence of the residual stresses, increasing the cooling rate, and increasing the diffusible hydrogen content in deposited metal, leading to the formation of brittle microstructures in heat-affected zone (HAZ). The paper presents the results of mechanical properties testing of S420G2+M steel welded joints made with covered electrodes in the water with salinity values: 0‰, 7.5‰, and 35‰. The non-destructive tests: ultrasonic (UT) and radiographic (RT), and destructive tests: Vickers HV10 measurements, Charpy impact, and bending and metallographic macro- and microscopic tests were performed. Moreover, the diffusible hydrogen content in deposited metal by the mercury method was measured. It was observed that water salinity has an influence on the stability of the welding arc and the properties of joints. In particular, it was found that increasing the water salinity provides to: decreasing the hardness of HAZ (from 211 HV10 to 193 HV10), increasing the impact strength (from 82.5 to 101.3 J/cm2). Additionally, a slight increase in the diffusible hydrogen content in deposited metal (up to 65 ml/100g) was observed. The number of microcracks in the joints decreased with increasing the water salinity.