Microbiologically corrosion is a critical factor contributing to the degradation of marine engineering infrastructure.Electrochemical methods and slow strain rate tensile(SSRT) tests were employed to evaluate the effect of cathodic protection (CP) on the corrosion behavior of X70 pipeline steel in marine environments containing sulfate⁃reducing bacteria (SRB).Together with microstructural characterization,the stress corrosion cracking(SCC) mechanism of X70 steel in SRB⁃containing marine environments was analyzed.The results indicate that CP potentials of -0.775,-0.850 V promoted SRB growth.When the CP potential reached -1.000 V,it not only promoted the proliferation of SRB but also accelerated their transition into the decline phase.In the absence of applied stress,the optimal CP potential for X70 steel in SRB⁃containing marine environments was -0.850 V.Without CP,the SCC mechanism of X70 steel was a hybrid mode involving anodic dissolution induced by the marine environment and hydrogen⁃induced cracking caused by SRB.At CP potentials of -0.775,-0.850 V,the SCC mechanism was dominated by SRB⁃induced hydrogen⁃induced cracking.When the CP potential was -1.000 V,the SCC mechanism was a hybrid mechanism jointly induced by anodic dissolution caused by the marine environment and hydrogen⁃induced cracking induced by the CP potential.The synergistic effect of SRB and CP significantly increased the hydrogen embrittlement susceptibility of X70 steel in marine environments.

The filtration and separation area of a station on the China?Russia East Route is set as parallel pipelines,and the uneven distribution of branch flow may occur due to the differences in internal pressure and pipeline layout,which affects the filtration efficiency and the overall work efficiency.In order to avoid pipeline bias, the flow direction of the filtration and separation area is studied based on computational fluid dynamics (CFD).Results show that pressure distribution, turbulent flow distribution, frictional resistance loss along the system,fluid inertia and other factors affect the branch pipe flow distribution.Among 11 parallel pipeline configurations,the axial inlet and radial outlet configuration (Type 3) with inlets and outlets on the same side exhibits the least flow maldistribution overall.Under normal working conditions,flow maldistribution decreases with increasing manifold diameter and branch pipe spacing within the calculation range.Fault conditions,such as branch pipe blockages,significantly exacerbate flow maldistribution in the system.It is concluded that the flow distribution rule and the main factors affecting the flow distribution are obtained,which is helpful to guide the design and construction of gas transmission station.