Hydrogen blended with natural gas is one of the best ways for large-scale hydrogen transportation; however, pipeline steels exploited for transferring natural gas have the risk of hydrogen embrittlement. Therefore, the hydrogen damage mechanism and resistance property of different steel pipelines should be carefully examined to select suitable materials for the task mentioned above. The common X42, X52, X70, and AISI 1020 are taken into account as research objects. Their mechanical properties and hydrogen absorption properties in a hydrogen environment are investigated to explore further factors affecting the hydrogen embrittlement of material. Dynamic slow strain rate tensile test results show that these materials exhibit varying hydrogen embrittlement sensitivity in a hydrogen environment. AISI 1020 has the highest hydrogen embrittlement susceptibility, then X70, and X42 presents the lowest one. Generally, hydrogen embrittlement behaviours are strengthened by increasing the current density. As the current density grows, the fracture mode of pipeline steels transforms from the ductile fracture to the quasi-cleavage fracture and finally turns into the cleavage fracture. The hydrogen embrittlement fracture of the tensile specimen results from the action of the HEDE and HELP in various zones. TDS test results indicates that the content of C and Mn significantly influence on the hydrogen solubility in metal materials.

Decanter centrifuges are widely used for solid–liquid separation. Although parameter analysis for decanter centrifuges was performed by numerical simulation in previous studies, some structural parameters are rarely mentioned and investigated. At the same time, the results obtained by the single-parameter analysis in previous studies are difficult to truly realize the comprehensive performance optimization of decanter centrifuges. In this paper, the influences of the window structure and bowl–conveyor gap on the separation performance are systematically analyzed with the employment of a numerical computation method. The results show that the increase in the window angle and window height will accelerate the flow of the upper layer, while the increase in the bowl–conveyor gap may make particles flow through it directly and further form a solid retention zone. Both of the structural changes will lead to deterioration of the separation performance. On the basis of numerical simulation analysis, a genetic algorithm-based method for multiparameter optimization is proposed in this paper. Parameter optimization shows that bowl speed and feed flow rate have the most significant effects on the separation performance and power consumption. Compared with the minimal specific power in the first generation, the optimized specific power is reduced by 15.7%, and the cake solid content merely decreases by 0.044%.

No abstract

With the development of renewable energy, hydrogen energy is paid more and more attention. Hydrogen is an excellent energy carrier, but it is difficult to store and transport because of its special properties. Hydrogen blended with nature gas is considered to be one of best transition solutions to solve the problem of large-scale hydrogen transportation. But hydrogen embrittlement occurs when the pipeline steel used to transport natural gas is exposed to hydrogen environment. Referencing to ASME B31.12, X42 pipeline steel is selected as the research object in this paper. And the mechanical properties of X42 were tested by electrochemical hydrogen charging, slow strain rate tensile (SSRT) test and fatigue crack growth (FCG) test combined with thermal desorption spectroscopy (TDS) and SEM. Hydrogen adsorption properties of X42 pipeline steel at room temperature was measured by TDS. SSRT test showed that the strength of X42 strengthened slightly in electrochemical hydrogen charging environment, but the plasticity decreased significantly, and the embrittlement degree of materials increased with the elevated current density. FCG test showed that the presence of hydrogen will accelerate the crack growth rate and reduce the fatigue life of materials. SEM images of tensile and fatigue specimens showed that hydrogen transforms the fracture mode from ductile fracture to cleavage fracture.