Anti-corrosion technology for OCTG pipes

1. Cathodic protection technology
Cathodic protection method is a widely used and relatively mature oil and gas pipeline protection technology. The cathodic protection method can be divided into: impressed current cathodic protection method and sacrificial anode cathodic protection method according to different power supply current methods. The selection of protection methods should be based on the actual environment and pipeline parameters. Generally, the impressed current cathodic protection method is used, and high-quality materials such as graphite are selected to give full play to the role of the cathodic protection method. When crossing railways, highways, rivers or river belts, etc., since the casing of the pipeline belt has a shielding effect, it is advisable to use the sacrificial anode protection method of zinc, magnesium, aluminum and their alloy anodes as anodes. Oil and gas pipelines have complex conditions such as anti-corrosion coatings, soil environment, stray currents, and parallel pipelines. At the same time, magnetic storms will generate geomagnetic induction currents in oil and gas pipelines, which will interfere with cathodic protection equipment. The application of cathodic protection in oil and gas pipeline protection is still limited. There are many issues to be studied.

2. Corrosion inhibitor technology
Anti-corrosion mechanism of corrosion inhibitors: Corrosion inhibitors form a protective layer on the pipeline surface to slow down corrosion through physical adsorption and chemical adsorption of polar groups on the molecules, or a combination of both. Physical adsorption characteristics: The adsorption speed is relatively fast and has certain reversibility. Characteristics of chemical adsorption: strong adsorption capacity, irreversible, and slow speed. Anti-corrosion inhibitors for oil and gas pipelines are mainly imidazolines, amines, organophosphates, morphines, acetylenic alcohols, including heterocyclic compounds of N, P, S and O, etc. Corrosion inhibitor anti-corrosion technology has broad application prospects because of its advantages of simple operation, low cost, and quick results. At the same time, corrosion inhibitors suitable for complex and diverse environments (such as high temperature and pressure, high-speed media flow, and shear stress) still require further research.
3. Anti-corrosion coating technology
Anti-corrosion coating is a simple, fast and effective anti-corrosion technology. It has the characteristics of simple preparation process, low cost and no geographical restrictions. Adding a layer of anti-corrosion coating to the surface of oil and gas pipelines can not only isolate external current, but also prevent some plant roots from passing through, playing an effective anti-corrosion role in 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, sintered epoxy powder, petroleum asphalt, extruded polyethylene, coal tar enamel and epoxy coal pitch wait. Research on new anti-corrosion coatings and anti-corrosion materials is one of the hot trends in metal anti-corrosion. New anti-corrosion coatings not only focus on anti-corrosion but also focus on additional functions such as super-hydrophobic, anti-fouling, self-healing, heat-resistant and anti-bacterial. Some studies have pointed out that the anti-corrosion mechanism of graphene lies in its shielding, corrosion inhibition, reinforcement and cathodic protection functions, and proposed improvement measures for its existing problems such as easy agglomeration, difficulty in directional arrangement, and defects in its own structure. At present, there is still relatively little research on graphene anti-corrosion. Improper use not only fails to achieve the anti-corrosion effect but also promotes corrosion, hindering the application and development of this anti-corrosion coating. Graphene oxide has a structural strength similar to graphene and has superior mechanical strength, chemical and thermal stability, and is considered an excellent graphene substitute. Graphene oxide is not only hydrophobic, but also can reduce the adsorption and migration of corrosive substances, effectively improving the corrosion resistance of the composite coating. DAN et al. used atomic polymerization to graft polyurethane (PU)/polypropylene oxide and graphene oxide (GO-g-PPO). Research shows that the GO-g-PPO-16 composite material is evenly dispersed in the PU coating, which greatly improves the anti-corrosion performance of the PU/GO-g-PPO-16 composite coating. Experimental results show that when the solid content of the GO-g-PPO-16 composite in the PU coating is 0.08% (mass fraction), after immersing in a 3.5% mass fraction NaCl solution for 168 h, the resistance of the coating is PU 50 times the coating.

4. Sealing technology
The patching technology uses primer paint to apply to the corrosion gap, and the outside is often wrapped with polyethylene tape, thereby improving the external performance of the pipeline and effectively protecting the oil and gas pipeline. When there is a gap in the oil pipeline, repairing it with patching technology can ensure the integrity of the pipeline. Commonly used patching technologies include: hot asphalt pouring patching technology and polyethylene material patching technology. Sealing technology plays an important role in ensuring the integrity of pipelines. Failure of seaming will lead to corrosion defects in the pipeline. Domestic oil and natural gas pipelines mostly use 3LPE anti-corrosion coating, and the corresponding patching material is generally heat shrink tape. The failure of the heat shrink tape will lead to oil and gas leakage. Li Haikun et al. studied the degradation of hot melt adhesive after aging of heat shrinkable tape, the relationship between water absorption, peel strength and damage properties, and degradation of hot melt adhesive after aging at different temperatures and times. Research shows that the failure properties of heat shrinkable tapes and peeling tests are highly correlated with the high-temperature water absorption of hot melt adhesives, but are less correlated with the degradation of hot melt adhesives. The higher stability is the occurrence of cohesive failure and hot melt Heat shrinkable tape with low water absorption at high temperatures and for a long time.
5. Composite pipe technology
Composite pipe technology has the characteristics of good mechanical properties, corrosion resistance and good economy. Bimetal-lined composite pipes are the most common, consisting of an inner liner pipe and an outer base pipe. Chen Junwen et al. established a finite element model for process mechanics analysis of bimetal-lined composite pipes and simulated the pipe making process. Research shows that the tightness of the two pipes of the bimetal-lined composite pipe increases with the increase of the internal pressure, and decreases with the increase of the difference in expansion coefficient of the two materials. To improve the tightness, the internal pressure, Reduce the difference in expansion coefficients between the two materials. Bimetallic composite pipe materials are difficult to weld due to their special materials and are prone to welding defects. Studies have shown that after a 720-h corrosion test, the X52/825 metallurgical composite pipe welded joint did not show cracks, punctures, or cracks, indicating that the welded joint has good corrosion resistance. Today's bimetal composite pipe collapse test, tightness test and bending test indicators are unclear, and the manufacturing, inspection and application of composite pipes require further research and improvement.