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In recent years, as for the frequent occurrence of failure accidents of high-grade steel pipelines caused by girth weld cracking, great attention has been drawn to the quality of girth weld and defect repair of high-grade steel pipelines. In terms of the types of girth weld defects of high-grade steel pipelines, the recommended treatment methods for girth weld defects in domestic and foreign repair standards for high-grade steel pipes were introduced, and the research results of the existing welding and non-welding repair technologies were systematically combed. As for welding repair technology, Type B sleeve is the preferred repair technology for repairing high-grade steel pipe girth weld defects. At present, the full-automatic welding technology for horizontal straight welds and circumferential fillet welds for open tee, guard plate and Type B sleeve has basically met the conditions for popularization and application, and is expected to greatly improve the welding efficiency and welding quality. Non-welding repair technology divides into three types: composite material, epoxy sleeve and steel lining composite material repair technology. A series of verification tests were conducted abroad to repair the defects (50% incomplete fusion) of X42 pipeline girth welds with composite materials and steel lining composite materials. Compared with composite materials, steel-lined composite materials perform better in axial tensile load test. In China, steel epoxy sleeve was used to reinforce the girth weld, which was inspected and evaluated to be unnecessary to repair but has defects, and the composite steel lining repair technology was designed based on the composite material and epoxy sleeve repair technology. Finally, the solution and key research directions were put forward to solve the problem of girth weld defect repair of high-grade pipelines, and supposed to provide technical reserves for the safe operation of China–Russia Eastern Gas Pipeline Project and similar high-grade pipelines.

In order to improve the operation performance of microbial fuel cells, improved the degradation rate of nitrate and the power output of microbial fuel cell, a typical single chamber air-cathode microbial fuel cell (AC-MFC) is inoculated and operated with urban sewage treatment plant clarifier sludge as inoculum source and sodium nitrate as electron acceptor. It is successfully started by synthetic wastewater containing a phosphate buffered nutrient solution (PBS, 50 mmol/L) and sodium acetate (1 g/L). After successful starting, the four factors of carbon source, C/N, nitrate concentration and temperature are considered to optimize the operation performance of MFC. The test result shows that the operation performance of MFC is best under the conditions of anhydrous sodium acetate as carbon source, C/N of 5∶1, 200 mg/L nitrate concentration and at 30 ℃, and the degradation rate of nitrate reaches more than 90% and the voltage of MFC is 0.462 V. After 6 cycles of operation, the voltage and power density of MFC reaches 0.62 V and 4.53 W /m2. AC impedance analysis indicates that the MFC resistance is 130 Ω. Scanning electron microscopy of electrode surface illustrates that the number of microbial species are significantly increased. The results indicate that MFC can be an effective technology for nitrate contained wastewater treatment and energy production.