Hydrogen permeation in a Cr–Mo–V medium-carbon steel: Effect of the quenching medium and tempering temperature

Hydrogen permeation tests are carried out to evaluate the effect of the quenching medium and tempering temperature on the permeation parameters and density of hydrogen traps, of a Cr–Mo–V low-alloy medium-carbon steel. Three types of steel membranes are tested: 1) in the as-quenched condition, 2) tempered at 235 °C and 3) tempered at 530 °C; each one quenched in two different media: oil or brine. From the as-quenched condition, the apparent concentration of hydrogen and hydrogen flux, tend to decrease as the tempering temperature increases. The membranes in the as-quenched condition and tempered at 530 °C, show lower hydrogen diffusivity and higher density of hydrogen traps than membranes tempered at 235 °C. It is concluded that tempering at 235 °C, promotes hydrogen induced cracking, which is contrary to what has been previously determined. The cracking is related to a higher hydrogen diffusivity and lower density of hydrogen traps.     

Heat treatment method for making high strength and conductivity Cu–Cr–Zr alloy

Abstract

In this paper, the heat treatment called ‘a two-step aging process’ with the feature of the first step aging at a low temperature for a long time and the second step aging at a higher temperature for a short time has been proposed. Applying this process, the Cu–Cr–Zr alloy possessing both high strength and high conductivity can be acquired due to the formation of numerous tiny particles precipitated fully out from Cu matrix.     

Influence of high pressure hydrogen on the tensile and fatigue properties of a high strength Cu–Al–Ni–Fe alloy

Aluminum bronze CW307G was tensile and fatigue tested in 10 MPa hydrogen, 10 MPa helium and 0.1 MPa air atmosphere. Neither tensile nor S–N fatigue properties were affected when testing in H₂. Fractography on the fatigue specimens revealed similar striation morphology on the specimens tested in H₂ and He. Dissociative chemisorption as well as hydrogen absorption were identified as potential rate limiting processes being responsible for the impassivity to HEE of this alloy.     

Optimisation of post-weld heat treatment of a 1.25Cr–0.5Mo pressure vessel for high temperature hydrogen service

The ASME pressure vessel design code permits a range of post-weld heat treatment temperatures for 1.25Cr–0.5Mo pressure vessels. Studies using analytical transmission electron microscopy, X-ray diffraction, hardness and Charpy toughness testing, were performed on material from a new pressure vessel to understand the effects of various heat treatment schedules allowed within the code. These techniques have enabled an optimum heat treatment temperature and the time to be determined, with a view to minimising the likely susceptibility of the vessel to temper embrittlement and hydrogen attack.     

Study on fracture strain of Cr–Mo steel in high pressure hydrogen

Cr–Mo steel is often used as the material of the hydrogen storage vessel, but its ductility can be deteriorated by high pressure hydrogen, which makes it possible that the local area of strain concentration on the hydrogen storage vessel made of Cr–Mo steel may fail due to excessive plastic deformation. The limit criterion of local strain established according to the study of the fracture strain is the basis for local failure assessment of the vessel. However, the correlation between the fracture strain and the stress state of Cr–Mo steel in high pressure hydrogen is still unclear, so the limit criterion of local strain for hydrogen storage vessel made of Cr–Mo steel has not been established. In this paper, the slow strain rate tensile test (SSRT) of notched specimens with different notch sizes was carried out in air, 45 MPa hydrogen and 100 MPa hydrogen, respectively. Based on the test results, the whole process from tensile to fracture of the specimens was simulated by finite element method. The distribution of stress triaxiality and plastic strain during the tensile process was analyzed, and the correlations between the stress triaxiality and the fracture strain in different environments were obtained. Finally, the limit criterion of local strain for local failure assessment of 4130X hydrogen storage vessel was established.     

S–N fatigue properties of a stable high-aluminum austenitic stainless steel for hydrogen applications

The fatigue properties of a novel high aluminum austenitic stainless steel with a high resistance against hydrogen embrittlement were investigated. S–N tests in 40 MPa H₂ at −50 °C resulted in a reduction in fatigue life by a factor of about 2 compared to air. Striation analysis revealed no acceleration of crack growth rate but accelerated crack initiation or accelerated short crack growth in H₂. No apparent difference in fatigue fracture characteristics and striation morphology between the air and H₂ tested specimens could be identified.     

Effect of high temperature deformation on the microstructure,mechanical properties and hydrogen embrittlement of 2.25Cr–1Mo-0.25 V steel

In this paper, the effects of high temperature deformation on the microstructure, mechanical properties and hydrogen embrittlement (HE) of the 2.25Cr–1Mo-0.25 V steel was investigated by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and tensile tests. The SEM and TEM images demonstrated that high temperature plastic deformation (HTPD) led to the coarsening of carbides and the dislocation density increase. The tensile tests displayed that the HTPD resulted in the cracking susceptibility increase, as indicated by the increased numbers and sizes of cracks at the fractured surface. This was attributed to the coarsening of carbides during high temperature deformation. In contrast, the HTPD highly decreased the loss of ductility compared to the un-deformed specimens, although the amount of ductility losses (elongation or reduction of area) did not change significantly as the HTPD increased. The correlations among carbides, hydrogen and cracks were discussed.     

Characterization of high strength and high toughness Ni–Mo–Cr low alloy steels for nuclear application

The reactor pressure vessels of PWRs have mostly been made of SA508 Grade 3 (Class 1) low alloy steels which have revealed moderate mechanical properties and a moderate radiation resistance for a 40 or 60 year operation. The specified minimum yield strength of the material is 345 MPa with a ductile–brittle transition temperature of about 0 °C. While other materials, most of which are non-ferrous alloys or high alloyed steels for a higher temperature application, are being developed for the Generation-4 reactors, low alloy steels with a higher strength and toughness can help to increase the safety and economy of the advanced PWR systems which will be launched in the near future. The ASME specification for SA508 Grade 4N provides a way to increase both the strength and toughness by a chemistry modification, especially by increasing the Ni and Cr contents. However, a higher strength steel has a deficiency due to a lack of operating data for nuclear power plants. In this study, experimental heats of SA508 Grade 4N steels with different chemical compositions were characterized mechanically. The preliminary results for an irradiation embrittlement and the HAZ properties are discussed in addition to their superior baseline properties.     

Hydrogen–steel interaction: hydrogen embrittlementin pipes for power former plant effluents

The steel industrially employed for the transport of liquid hydrocarburics in thepresence of hydrogen at high temperatures is ASTM A335 P11, a steel for seamless pipes for useat high temperature. Three different kinds of tests have been performed: tests of prenaturedfracture, tests of thermal analysis and infrared analysis. The present work has deeply studied themechanisms of interaction between hydrogen and steel, trying to integrate and motivate theindustrial data, commonly used for plant planning and sizing (A.P.I. Diagrams), proving that thecause for the damaging of this material is mainly due to the harmful interaction of carbides andinclusion with hydrogen.     

Hydrogen embrittlement associated with strain localization in a precipitation-hardened Fe–Mn–Al–C light weight austenitic steel

Hydrogen embrittlement of a precipitation-hardened Fe–26Mn–11Al-1.2C (wt.%) austenitic steel was examined by tensile testing under hydrogen charging and thermal desorption analysis. While the high strength of the alloy (>1 GPa) was not affected, hydrogen charging reduced the engineering tensile elongation from 44 to only 5%. Hydrogen-assisted cracking mechanisms were studied via the joint use of electron backscatter diffraction analysis and orientation-optimized electron channeling contrast imaging. The observed embrittlement was mainly due to two mechanisms, namely, grain boundary triple junction cracking and slip-localization-induced intergranular cracking along micro-voids formed on grain boundaries. Grain boundary triple junction cracking occurs preferentially, while the microscopically ductile slip-localization-induced intergranular cracking assists crack growth during plastic deformation resulting in macroscopic brittle fracture appearance.     

Ceria as a catalyst for hydrogen iodide decomposition in sulfur–iodine cycle for hydrogen production

In this work, ceria (CeO₂) prepared with different methods and at various calcination temperatures have been tested to evaluate their effect on hydrogen iodide (HI) decomposition in sulfur–iodine (SI) cycle at various temperatures. The CeO₂ catalysts' strongly enhance the HI decomposition by comparison with blank test, especially gel CeO₂ 300. TG–FTIR, BET, XRD, TEM and TPR were performed for catalysts' characterization. The results show that the CeO₂ catalyst synthesized by citric-aided sol–gel method and calcined at low temperature (<500 °C) shows more lattice defects, smaller crystallites, larger surface area and better reducibility. Oxygen can promote the significantly rapid surface reaction, but simultaneously consume hydrogen species (H) contained in HI. Lattice defects, especially the reduced surface sites, i.e., Ce³⁺ and oxygen vacancy, play the dominant role in surface reactions of HI decomposition. A new reaction mechanism for HI catalytic decomposition over CeO₂ catalyst is proposed.     

Fast hydriding Mg–Zr–Mn–Ni alloy compositions for high capacity hydrogen storage application

Hydrogen is one of the best alternative to petroleum as an energy carrier. However, the development of a Hydrogen-based economy requires commercialization of safe and cost-effective Hydrogen storage system. In this paper, alloys belonging to Mg–Zr–Mn–Ni alloy system are synthesized using high energy ball milling method. The particle size evolution, chemical analysis and nano-scaled structures were characterized by using SEM, EDXS and XRD techniques, respectively. The optimized - highest hydrogen storing - alloy has particle size of about 8.36 ± 1.17 μm with crystallite size 16.99 ± 5.48 nm. Hydrogen absorption-desorption measurement is carried out on the principle of pressure reduction method. The alloy coded with MZ1 shows uptake of greater than 7 mass % H₂ at a charging temperature of 200 °C, indicating high gravimetric hydrogen storage capacity at relatively lower hydriding temperature. The optimized Mg–Zr–Mn–Ni alloy also shows considerably enhanced hydriding – dehydriding kinetics, compare to pure Mg.     

Performance of a PV–wind hybrid system for hydrogen production

This paper describes the performance of an integrated PV–wind hydrogen energy production system. The system consists of photovoltaic array, wind turbine, PEM electrolyser, battery bank, hydrogen storage tank, and an automatic control system for battery charging and discharging conditions. The system produced 130–140 ml/min of hydrogen, for an average global solar radiation and wind speed ranging between 200 and 800 W/m² and 2.0 and 5.0 m/s respectively. A mathematical model for each component in the system was developed and compared to the experimental results.     

Unraveling the effect of dislocations and deformation-induced boundaries on environmental hydrogen embrittlement behavior of a cold-rolled Al–Zn–Mg–Cu alloy

The effect of dislocation substructure, and deformation-induced boundaries on the hydrogen embrittlement (HE) behavior and the fracture mechanism of a 7xxx series aluminum alloy was investigated using X-ray diffraction line-profile analysis, electron backscatter diffraction, transmission electron microscopy, thermal desorption spectroscopy, and visualization of hydrogen. Hydrogen resides at interstitial lattice sites, statistically-stored dislocations (SSDs), and high-angle boundaries (HABs). SSDs are not the main trap site affecting HE behavior of the alloy. However, the HABs with the high desorption energy act as an almost irreversible trap site, which strongly absorbs hydrogen. It was firstly reported that the higher density of HABs as a strong trap site in a deformed 7xxx series aluminum alloy leads to decreasing the possibility of building up a critical hydrogen concentration required for crack initiation in a typical HAB, resulting in an excellent hydrogen embrittlement resistance.     

The effect of hydrogen injection parameters on the quality of hydrogen–air mixture formation for a PFI hydrogen internal combustion engine

To research the quality of the hydrogen–air mixture formation and the combustion characteristics of the hydrogen fueled engine under different hydrogen injection timings, nozzle hole positions and nozzle hole diameter, a three-dimensional simulation model for a PFI hydrogen internal combustion engine with the inlet, outlet, valves and cylinder was established using AVL Fire software. In the maximum torque condition, research focused on the variation law of the total hydrogen mass in the cylinder and inlet and the space distribution characteristics and variation law of velocity field, concentration field and turbulent kinetic energy under different hydrogen injection parameters (injection timings, nozzle hole positions and nozzle hole area) in order to reveal the influence of these parameters on hydrogen–air mixture formation process. Then the formation quality of hydrogen–air mixture was comprehensively evaluated according to the mixture uniformity coefficient, the remnant hydrogen percentage in the inlet and restraining abnormal combustion (such as preignition and backfire). The results showed that the three hydrogen injection parameters have important influence on the forming quality of hydrogen–air mixture and combustion state. The reasonable choice of the nozzle hole position of hydrogen, nozzle hole diameter and the hydrogen injection time can improve the uniformity of the hydrogen–air mixing in the cylinder of the hydrogen internal combustion engine, and the combustion heat release reaction is more reasonable. At the end of the compression stroke, the equivalence ratio uniform coefficient increased at first and then decreased with the beginning of the hydrogen injection. When hydrogen injection starting point was with 410–430°CA, equivalence ratio uniform coefficient was larger, and ignition delay period was shorter so that the combustion performance index was also good. And remnant hydrogen percentage in the inlet was less, high concentration of mixed gas in the vicinity of the inlet valve also gathered less, thus suppressing the preignition and backfire. With the increase of the distance between the nozzle and the inlet valve, the selection of the hydrogen injection period is narrowed, and the optimum hydrogen injection time was also ahead of time. The results also showed that it was favorable for the formation of uniform mixing gas when the nozzle hole diameter was 4 mm.     

Preparation of Ni–P–La alloy as a novel electrocatalysts for hydrogen evolution reaction

Ternary Ni–P–La alloy was synthesized by the co-electrodeposition method on the copper substrate. The energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used for characterization of the synthesized alloy. The electrochemical performance of the novel alloy was investigated based on electrochemical data obtained from steady-state polarization, Tafel curves, linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) in alkaline solution and at ambient temperature. The results showed that the microstructural properties play a vital purpose in determining the electrocatalytic activity of the novel alloys. Also, the HER on investigated alloys was performed via the Volmer-Heyrovsky mechanism and Volmer step as RDS in this work. Ni–P–La catalyst was specified by ƞ₂₅₀ = −139.0 mV, b = −93.0 mV dec⁻¹, and j_o = −181.0 μA cm⁻². The results revealed that the Ni–P–La catalysts have a high potential for HER electrocatalysts in 1M NaOH solution.     

Corrosion resistances of alloys in high temperature hydrogen iodide gas environment for sulfur–iodine thermochemical cycle

The hydrogen iodide (HI) decomposition process is a limiting step for the efficiency of the sulfur–iodine nuclear hydrogen production process, owing to its low kinetics and complicated reaction characteristics. Therefore, the Korea Advanced Institute of Science and Technology (KAIST) suggested a simple high-temperature HI decomposition process at 650–700 °C for higher efficiency. For practical application of the high-temperature HI decomposition process, along with the catalyst study, we performed structure material selection and corrosion resistance tests. A number of candidate alloys were considered in various aspects and exposed to the high-temperature HI gas environment, which is extremely corrosive, at 850 °C for 100 h. Nine alloys with different nickel and iron compositions have been tested and analyzed. Test results indicated the degrees of resistances to corrosion of each alloy, on the basis of weight change and cross-sectional micrographs. Thus, because of their resistance to internal oxidation and formation of stable external oxide layers, five types of alloys, Haynes 214, aluminizing and inter-diffusion heat-treated or electron beam surface-treated Alloy 617 are suggested as appropriate candidates for fabricating high-temperature HI decomposer. In particular, surface-treatment of Alloy 617 gave it a high stability because of the resultant formation of an Al-rich layer; this was confirmed by experimental results, so IDHT Alloy 617 is recommended as a suitable structural material for fabricating HI decomposer. However, further long-term testing is suggested to ensure safety and confirm applicability.     

An exergy–cost–energy–mass analysis of a hybrid copper–chlorine thermochemical cycle for hydrogen production

An exergoeconomic assessment using exergy–cost–energy–mass (EXCEM) analysis is reported of a copper–chlorine (Cu–Cl) thermochemical water splitting cycle for hydrogen production. The quantitative relation is identified between capital costs and thermodynamic losses for devices in the cycle. A correlation detected in previous assessments, suggesting that devices in energy systems are configured so as to achieve an overall optimal design by appropriately balancing thermodynamic (exergy-based) and economic characteristics of the overall system and its components, is observed to apply for the Cu–Cl cycle. Exergetic cost allocations and various exergoeconomic performance parameters are determined for the overall cycle and its components. The results are expected to assist ongoing efforts to increase the economic viability and to reduce product costs of potential commercial versions of this process. The impacts of these results are anticipated to be significant since thermochemical water splitting with a copper–chlorine cycle is a promising process that could be linked with nuclear reactors to produce hydrogen with no greenhouse gases emissions, and thereby help mitigate numerous energy and environment concerns.     

Nanostructural Co–MoS2/NiCoS supported on reduced Graphene oxide as a high activity electrocatalyst for hydrogen evolution in alkaline media

There are many tremendous challenges to enhance the hydrogen evolution reaction (HER) activity of MoS₂. In this study, nanoflower-like Co–MoS₂/NiCoS structure supported on reduced Graphene Oxide (rGO) was rationally developed via a simple hydrothermal route, where the synergistic regulations of both interface structural and electronic conductivity were successfully presented by using controllable interface engineering and Co metal ions doped into MoS₂ nanosheets. Ascribed to the 3D flower-like nanostructure with massive active sites, the interface coupling effect between MoS₂ and Ni–Co–S phase, and Co-doped MoS₂ can modulate its surface electronic density. The optimal Co–MoS₂/NiCoS/rGO hybrid exhibits excellent HER activity in 1.0 M KOH, with a small overpotential (η₁₀, 84 mV) at 10 mA cm^?2 and a low Tafel slope (46 mV dec^?1), accompanied by good stability. This work provides an effective route to produce other electrocatalysts based on interface structure and electronic conductivity engineering for HER in the future.     

Optical efficiency of a PV–thermal hybrid CPC module for high latitudes

The advantage of PV–thermal hybrid systems is their high total efficiency. By using concentrating hybrid systems, the cost per energy produced is reduced due to simultaneous heat and electricity production and a reduced PV cell area. In this article, the optical efficiency of a water-cooled PV–thermal hybrid system with low concentrating aluminium compound parabolic concentrators is discussed. The system was built in 1999 in Älvkarleby, Sweden (60.5° N, 17.4° E) with a geometric concentration ratio of C=4 and 0.5 kW_p electric power. The yearly output is 250 kWh of electricity per square metre solar cell area and 800 kWh of heat at low temperatures per square metre solar cell area. By using numerical data from optical measurements of the components (glazing, reflectors, and PV cells) the optical efficiency, η_opt, of the PV–CPC system has been determined to be 0.71, which is in agreement with the optical efficiency as determined from thermal and electrical measurements. Calculations show that optimised antireflection-treated glazing and reflectors could further increase the electric power yield.