The core problem of low energy consumption anaerobic fermentation reactor is that the reactor can make reasonable and effective use of energy from two aspects of quantity and quality, so as to ensure the anaerobic fermentation performance of the reactor and make it run efficiently and energy-saving. However, serious corrosion of metal for reactors was found during operation, and the selection of reactor materials became the key to restrict biogas production. In this paper, the corrosion characteristics of the four metals including Q235A steel, Q345A steel, 45# steel and 3Cr13 steel were determined by corrosion morphology, mechanical and electrochemical experiments. The results showed that the corrosion product particles of Q235A steel were polygonal, showing a good cross-linking feature, which was better than that of Q345A and 45# steels. However, there was no obvious boundary between corrosion product particles of 3Cr13 steel. The presence of Fe3C in the corrosion products of 3Cr13 steel and the observation of micro-cracks on the surface at nanometer scale indicated that the intergranular corrosion of 3Cr13 steel was dominated. For another aspect, with the increase of CO2 and CH4 content, the corrosion rate of the four metals was generally accelerated, in which the Q235A steel showed the best performance under different conditions. In addition, Q345A and 45# steels showed relatively good corrosion resistance, under which the total mole of mixed gas (CO2/H2O/CH4) was lowest.

The mechanical characteristics and mechanisms of rock failure involve complex rock mass mechanics problems involving parameters such as energy concentration, storage, dissipation, and release. Therefore, it is important to select appropriate monitoring technologies to carry out relevant research. Fortunately, infrared thermal imaging monitoring technology has obvious advantages in the experimental study of rock failure processes and energy dissipation and release characteristics under load damage. Therefore, it is necessary to establish the theoretical relationship between the strain energy and infrared radiation information of sandstone and to reveal its fracture energy dissipation and disaster mechanism. In this study, an MTS electro-hydraulic servo press was used to carry out uniaxial loading experiments on sandstone. The characteristics of dissipated energy, elastic energy, and infrared radiation during the damage process of sandstone were studied using infrared thermal imaging technology. The results show that (1) the transition of sandstone loading from one stable state to another occurs in the form of an abrupt change. This sudden change is characterized by the simultaneous occurrence of elastic energy release, dissipative energy surging, and infrared radiation count (IRC) surging, and it has the characteristics of a short duration and large amplitude variation. (2) With the increase in the elastic energy variation, the surge in the IRC of sandstone samples presents three different development stages, namely fluctuation (stage Ⅰ), steady rise (stage Ⅱ), and rapid rise (stage Ⅲ). (3) The more obvious the surge in the IRC, the greater the degree of local damage of the sandstone and the greater the range of the corresponding elastic energy change (or dissipation energy change). (4) A method of sandstone microcrack location and propagation pattern recognition based on infrared thermal imaging technology is proposed. This method can dynamically generate the distribution nephograph of tension-shear microcracks of the bearing rock and accurately evaluate the real-time process of rock damage evolution. Finally, this study can provide a theoretical basis for rock stability, safety monitoring, and early warning.

Sulfate reducing bacteria (SRB) are considered as one of the main causes for the failures of buried metal pipes. Although many researchers reported that more negative cathodic protection potential was required in environments containing SRB, SRB would increase the concentration of hydrogen adsorbed on steel surface and thus lead to hydrogen embrittlement. In the study, the optimum cathodic protection (CP) potentials of X70 steel in bacterial and sterile media were evaluated with electrochemical impedance spectroscopy. The morphology and composition of corrosion products were characterized by a scanning electron microscope (SEM), an energy dispersion X-ray spectrometer (EDS), and an X-ray photoelectron spectrometer (XPS). The corrosion morphology of X70 steel in NS4 medium was pits and the corrosion in the bacterial medium was more serious than that in the sterile medium. The corrosion products of X70 steel were FeOOH and Fe2O3 in the sterile medium, whereas its corrosion products in the bacterial medium were FeOOH and FeS. When CP potential was -775 mV, SRB growth was promoted and the optimal protection effect on X70 steel was achieved in the bacterial NS4 medium. Pits were still observed under the biofilm and the corresponding corrosion mechanism was extracellular electron transfer (EET). When CP potential was -875 mV, X70 steel realized the optimal protection in the sterile NS4 solution. However, CO2 hydrolysis and SRB metabolism in the bacterial medium resulted in hydrogen-induced pits on X70 steel surface. When CP potential was -1025 mV, the growth of SRB was inhibited and severe hydrogen evolution corrosion occurred on X70 steel in bacterial and sterile NS4 media. The optimal CP potential for pipeline steel in the sterile medium may lead to hydrogen corrosion in the bacterial medium when H+ concentration was high.