Firstly, the corrosion characteristics of oil and gas seamless pipelines are mostly in complex soil environment, and corrosive media are transmitted. Therefore, the inner and outer walls of seamless pipelines are likely to be corroded. Once the pipeline is corroded and perforated, oil and gas will leak. Not only is transportation disrupted, but also the environment will be polluted, and even disastrous accidents such as fires will be very dangerous.


The corrosion of oil and gas pipelines is different due to the environment and transmission media. The corrosion mechanism can be divided into chemical corrosion and electrochemical corrosion, especially electrochemical corrosion. Internal corrosion is the formation of water medium and original film in pipeline wall. Electrochemical corrosion occurs in gas pipeline. Some harmful impurities such as H2S, CO2 and other metals are directly caused by chemical corrosion. Corrosion mostly concentrated in elbow, low-lying water, gas-liquid interface and so on. External corrosion can be divided into overhead lines and buried pipelines. The former is susceptible to atmospheric corrosion, while the latter is susceptible to soil erosion, bacterial corrosion and stray current corrosion. There are many factors affecting soil erosion, such as soil pH, redox potential, soil resistivity, salt type and content, water content, porosity, organic matter content and temperature. One of the most common and harmful factors is the difference of soil media caused by macro-corrosion cells, such as the difference of soil salinity, soil permeability and soil temperature caused by soil concentration. Pipelines have strong corrosion tendency in high salinity and weak permeability of soil. Sometimes this is true. The potential difference between the two parts of the macro battery steel pipe can reach about 0.3V, and the distance between the two poles is several kilometers. The main cause of serious corrosion of buried pipeline is the battery in this system.


Second, the corrosion control methods of oil and gas pipeline corrosion control are: selecting corrosion resistant materials, coating protection, adding corrosion inhibitors; electrical protection, improving the environment. This paper mainly discusses the corrosion control of pipelines. At present, the common anticorrosive scheme of pipeline is the joint protection of external coating plus cathodic protection. The joint protection makes the means of corrosion control complement each other, reduces the cost of corrosion control, is economical, reasonable, safe and reliable. It has become a common method of corrosion protection of surface and water pipelines in developed countries in the world.


The buried pipeline coating increases the metal corrosion resistance of the battery circuit and reduces the corrosion current in the isolation environment such as steel pipe and soil corrosion, thus the corrosion control is carried out. However, in the pipeline anti-corrosion structure, due to pipeline transportation, construction conditions and many other factors, the coating can not be completely damaged, the damaged wall of the coating is easy to corrode, and because of the formation of corrosion battery small anode/large cathode conditions, corrosion current density, corrosion rate is often doubled. It can be seen that only the use of coatings can not completely prevent pipeline corrosion. According to the principle of electrochemical corrosion, as long as the metal is protected into a cathode, corrosion can be prevented. Therefore, the pipeline can be adequately protected by the auxiliary anode passing through the DC pipeline and the pipeline potential reaching -0.85V. That is to say, the method provides sufficient cathodic polarization current for the tube body at the damaged coating, and effectively protects the pipeline. Cathodic protection investment generally accounts for about 1% of the total pipeline investment, which can greatly improve the service life of pipelines. Since the 1970s, many developed countries in the world have explicitly stipulated in industrial regulations that long-distance pipelines must be protected by cathodic protection. In 1984, the Ministry of Crude Oil of China stipulated in SYJ7-84 Code for Design of Anti-corrosion Engineering for Steel Pipes and Tanks that cathodic protection must be used for oil and natural gas pipelines.


Environmental isolation such as steel pipe and soil corrosion caused by the use of external coatings is the basic means of corrosion of buried pipelines. As pipelines extend to deserts, swamps, permafrost and oceans, as well as the diversification of transport media, coatings need to meet more stringent environmental and technological conditions, and have longer service life. The development of chemical industry has promoted the progress of pipeline anticorrosion technology. New materials, processes and materials