Oil and gas pipelines are affected by the quality of their pipes, transportation medium, laying environment, and management design. Therefore, corrosion of the pipeline is inevitable. This increases the risk of oil and gas leaks. Oil and gas leakage will bring great harm to the human body, environment, and economy.
The distribution of oil and gas is not consistent with the market distribution. Therefore it is necessary to allocate resources. Compared with other modes of transportation, pipeline transportation has many advantages. For example, pipeline transportation has the advantages of low cost, high efficiency, short construction period, safety and pollution-free, can transport a variety of media, and can pass through various areas. In most parts of the world, oil and gas transport is mainly by pipeline. Metal pipes are affected by transportation media and environmental factors and corrosion is inevitable. As a result, corroded pipes experience reduced service life, reliability, and safety. Oil and gas leakage caused by pipeline corrosion will bring economic losses to enterprises. In addition, it will cause great damage to the environment. With the improvement of people’s awareness of environmental protection, people pay more and more attention to the harm caused by oil and gas leakage to the environment. Therefore, the research on corrosion and protection of oil and gas pipelines is of great significance.
Forms of Pipeline Corrosion
There are two main forms of pipeline corrosion: internal corrosion and external corrosion. Pipeline material, transportation medium, environment, management and design are all key factors that cause pipeline corrosion.
Pipeline quality factors: Today’s oil and gas transportation mostly uses steel with strong gold properties as pipeline materials. The steel pipe is subjected to the electrochemical, chemical and physical effects of the surrounding environmental medium, which will cause corrosion.
Transport medium factors: the oil and gas medium transported often contains water vapor, SO2, H2S and CO2. These react to form compounds that can clog pipes. So this leads to further corrosion of the pipe.
Environmental factors: Oil and gas pipelines are often laid underground. The outer surface of the pipe is covered with soil. The soil contains water, stray currents, and various salts. And there are microorganisms and bacteria inside the soil. These will lead to chemical corrosion and electrochemical corrosion of oil and gas pipelines. The process of oil and gas transportation is often accompanied by stress. Stress induced fluctuations caused corrosion and minor ruptures of pipes. Prolonged expansion can lead to the formation of large fractures. The erosion of oil and gas in the pipe and rain outside the pipe will cause the metal surface of the pipe to be exposed continuously, resulting in corrosion.
Management design factors: insufficient professional level of management personnel and pipeline loading and unloading, placement and construction do not comply with the rules will lead to pipeline corrosion.
Pipeline Anti-corrosion Technology
Cathodic protection technology Cathodic protection technology is a widely used and relatively mature oil and gas pipeline protection technology. Cathodic protection can be divided into impressed current cathodic protection and sacrificial anode cathodic protection according to different power supply current modes. The choice of protection method should be based on the actual environment and pipeline parameters, under normal circumstances, the impressed current cathodic protection law is used, and high-quality materials such as graphite are selected to give full play to the role of cathodic protection law.
In the case of crossing railway, highway, river or river belt, because the casing of the pipeline belt has a shielding effect, it is advisable to use zinc, magnesium, aluminum and its alloy anode as the sacrificial anode protection. Oil and gas pipeline has many complicated conditions such as anti-corrosion coating, soil environment, stray current and parallel pipeline, and magnetic storm phenomenon will cause geomagnetic induction current in oil and gas pipeline, which will cause interference to cathodic protection equipment. There are many problems to be studied in the application of cathodic protection in oil and gas pipeline protection.
Corrosion Inhibitor Technology
Corrosion inhibitor anticorrosion mechanism: Corrosion inhibitor through the physical adsorption and chemical adsorption of polar groups on the molecule or the combination of both on the pipeline surface to form a protective layer to slow down corrosion.
Physical adsorption characteristics: the adsorption speed is relatively fast and has certain reversibility.
Chemical adsorption characteristics: adsorption capacity is strong, irreversible, slow. Oil and gas pipeline corrosion inhibitors are mainly imidazolines, amines, organophosphates, morines, alkynols, including N, P, S and O heterocyclic compounds.
Some scholars have verified a new type of corrosion inhibitor. The results show that the corrosion inhibition effect of the inhibitor on the experimental Wells with different materials is more than 80%. Among them, the corrosion inhibition effect of 20# steel and N80 is similar to that of 16Mn.
The novel imidazoline derivative corrosion inhibitor has the best corrosion inhibition effect when the inhibitor group is divided into 20% corrosion inhibitor main agent + 10% scale inhibitor + 4% dispersing agent + 3% synergist + 63% water. The corrosion inhibitor is superior to the other 4 kinds of corrosion inhibitors. The results also show that the effects of corrosion inhibitors are synergistic, scale inhibitor and dispersant in order from large to small. JEVREMOVIC et al. studied a new method of low carbon steel corrosion inhibition by injecting corrosion inhibitor into the foam base, and the study showed that periodic treatment with foam containing TOFA/DETA imidazoline corrosion inhibitor could effectively reduce the top corrosion of low carbon steel. Corrosion inhibitor anticorrosion technology has broad application prospects because of its advantages of simple operation, low cost and quick effect. At the same time, corrosion inhibitors suitable for complex and diverse environments (such as high temperature and pressure, high speed flow of medium, and shear stress) still need further research.
Anticorrosive Coating Technology
Anticorrosive coating is a simple, fast and effective anticorrosive technology, which has the characteristics of simple preparation process, low cost and no geographical restrictions. Adding a layer of anti-corrosion coating to the surface of the oil and gas pipeline can not only isolate the external current, but also prevent the passage of some plant roots. This has an effective anti-corrosion effect on oil and gas pipelines.
There are many types of anti-corrosion coatings, such as room temperature curing ceramic anti-corrosion coating, three-layer composite coating, polyethylene adhesive tape, fused epoxy powder, petroleum asphalt, extruded polyethylene, coal tar enamel and epoxy coal asphalt. The research of new anti-corrosion coatings and anti-corrosion materials is one of the hot trends of metal anti-corrosion.
The new anti-corrosion coating not only focuses on anti-corrosion but also focuses on additional functions such as super hydrophobic, anti-fouling, self-healing, heat resistance and antibacterial. Yao-yao Sun et al. conducted a study on graphene anticorrosive coating, and pointed out that the anticorrosive mechanism of graphene lies in shielding, corrosion inhibition, reinforcement and cathodic protection, and put forward improvement measures for its problems such as easy agglomeration, difficult directional arrangement and defects in its own structure. At present, the research on graphene anticorrosion is still relatively few, and improper use not only does not play the role of anticorrosion, but also promotes corrosion, hindering the application and development of this anticorrosive coating.
Graphene oxide is similar in structural strength to graphene, has superior mechanical strength, chemical and thermal stability, and is considered to be an excellent alternative to graphene. Graphene oxide is not only hydrophobic, but also can reduce the adsorption and migration of corrosive substances, and effectively improve the corrosion resistance of composite coatings. DAN et al. used atomic polymerization to graft polyurethane (PU)/polypropylene oxide and graphene oxide (GO-g-PPO). The results show that GO-G-POP-16 composite material is uniformly dispersed in PU coating, which greatly improves the anticorrosive performance of PU/ GO-G-POP-16 composite coating. The experimental results show that when the solid content of Go-G-PO-16 composite in PU coating is 0.08% (mass fraction), the resistance of the coating is 50 times that of PU coating after soaking in 3.5% NaCl solution for 168 h.
