A negative disturbance simulation experiment of X60 steel was carried out in different soil environment. The influence of soil environment on the hydrogen embrittlement sensitivity of material was obtained by comparing the area shrinkage and elongation after fracture of pipeline substrate under different soil environment. The results show that the hydrogen embrittlement susceptibility of X60 steel in the soil of Tanglang Mountain increases with the negative shift of cathodic protection potential (the increase of cathodic current density). The hydrogen embrittlement susceptibility of X60 steel in the soil of Tanglang Mountain is less than 5% when the cathodic protection potential is less than -1.07 V vs. CSE (the current density is less than -0.1 mA/cm2). and the risk of hydrogen embrittlement is low; When the cathodic protection potential exceeds -1.1 V vs. CSE (current density exceeds -0.3 mA/cm2), the hydrogen embrittlement sensitivity coefficient exceeds 35%, and there is a certain risk of hydrogen embrittlement.
With the rapid development of China's economy, energy and transportation industries have developed rapidly, and more and more oil and gas pipelines and urban rail transit have been built and put into use. Urban rail transportation systems, such as subways or light rail, generally use direct current traction and backflow through the rail. Because the track is not completely insulated from the earth, it is inevitable that some electric current will be discharged from the track to the earth to form stray electric current, which will cause interference to the surrounding metal components such as buried oil and gas pipelines. The distribution of stray current varies with the train running time, so the dynamic fluctuation is a typical characteristic of the interference of rail transit to oil and gas pipelines [1]. With the development of urban rail transit and oil and gas pipelines in China, the interference of dynamic DC stray current in buried pipelines is becoming more and more serious [2]. Under AC-DC negative interference conditions and forced discharge measures, the negative potential on the pipeline is far more cathodic than the standard requirements. When the pipeline potential is too negative, large-scale hydrogen evolution reaction occurs on the surface of the pipe, and hydrogen production from the cathode enters the pipe easily causing the risk of hydrogen embrittlement. In particular, in the manufacturing and repair process of pipeline welding joints, elbows, b-type sleeve welding parts and other special positions, it is inevitable to be affected by assembly stress, heat treatment process and other factors, prone to local tissue hardening [3]. In addition, in the process of installation and service, pipelines are prone to local plastic deformation caused by third-party external force damage, or even local remelting of pipeline surface caused by lightning strike, which may lead to increased sensitivity of local hydrogen embrittlement of pipelines, and hydrogen embrittlement failure is more likely to occur under the condition of over-negative potential [4].
