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Common Defects and Countermeasures of Anticorrosion and Protection of Long-distance Natural Gas Steel Pipe

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1. The importance of anti-corrosion of long-distance natural gas anti-corrosion steel pipes

At this stage, both domestically and foreign, the demand for natural gas is gradually increasing, among which natural gas has become an irreplaceable and important energy source. In this case, the demand for natural gas will continue to rise until new and efficient energy sources appear and before mass production cannot be carried out. To ensure the supply requirements of natural gas, it is very important to protect the long-distance natural gas pipelines accordingly. Although in recent years, pipelines are the safest and least-consuming natural gas transportation method, the number of pipeline accidents has also gradually increased at this stage, which proves that there are also defects in the process of pipeline transportation. The most common cause of pipeline accidents is metal corrosion. In the actual pipeline transportation process, the possible hazards caused by pipeline corrosion include the following aspects: Once the pipeline is severely corroded, the corrosion products will be mixed with the natural gas in it, resulting in impurities mixed in the natural gas, which will seriously affect the natural gas. quality. Second, if the pipeline corrosion is very serious, it is very likely to cause natural gas leakage, which will not only cause serious loss of natural gas resources but also cause serious property damage to pipeline companies. Third, if the degree of corrosion reaches the level of possible leakage, the leaked natural gas will enter the soil, thereby causing serious pollution to the environment, and such damage to the environment is irreversible. At this stage, the problem of environmental protection is becoming more and more prominent. Under this circumstance, serious pollution to the environment will seriously limit the development of natural gas resources. Fourth, once the leaked natural gas directly encounters the fire source, it is very easy to cause fire and explosion accidents, which will not only affect the transportation of natural gas but also cause casualties. Fifth, after the pipeline is corroded, the corrosion products will adhere to the inner wall of the pipeline, thereby accelerating the corrosion process of the pipeline. Therefore, in the actual application process of natural gas pipeline transportation, pipeline anticorrosion is of great significance.

2. Anti-corrosion measures for long-distance natural gas steel pipes

In the actual pipeline transportation process, in essence, pipeline corrosion is a normal phenomenon and cannot be completely avoided. Reducing the impact of pipeline corrosion on natural gas transportation can only be mitigated through the application of corresponding measures, thereby reducing the corrosion rate of pipelines. The anti-corrosion of long-distance natural gas pipelines can be studied from two aspects: physical and chemical. From the physical aspect, the main method is to add a coating. In the chemical aspect, the main method is electrochemical protection measures. In most cases, the actual pipeline protection will choose to use a combination of physical and chemical protection measures.

(1) Additional coating

The main methods of adding coatings include: First, coal tar enamel. Adding coal tar enamel outside the transportation area is a relatively mature protective measure at this stage. Coal tar enamel not only has a strong anti-corrosion function but also has a certain degree of insulation. It can prevent the pipeline from being affected by stray currents, which plays a very critical role in the protection of the pipeline. Due to the relatively long service life of coal tar enamel, its economy is relatively high, and most of them choose it as the main material for additional coatings. In addition, coal tar enamel also has some shortcomings in the use process, mainly in the following aspects: This technology has very high requirements for pipeline temperature. Once the temperature of the conveying pipeline exceeds the specified temperature of coal tar enamel, It will cause the melting of coal tar enamel, which not only fails to protect the pipeline but also is likely to cause environmental pollution, which in turn cannot protect the pipeline. Therefore, in the actual application process, attention should be paid to coal tar Tar enamel is not suitable for heating piping. Second, the mechanical properties of coal tar enamel are in a relatively poor state, and it is very easy to be interfered with by other external substances with high hardness. If there are many hard stones in the nearby soil, it will also cause serious damage to the anti-corrosion layer of coal tar enamel. Destruction, in this case, coal tar enamel is also not suitable for areas with high hardness of underground stones. Secondly, PE two-layer structure. The addition of the PE two-layer structure on the outside of the transportation pipeline is also a pipeline protection measure that is used more frequently at this stage. The PE two-layer structure not only has an efficient anti-corrosion function but also has a strong milk bacteria function, which interferes with bacteria around the pipeline. can have a strong inhibitory effect. At the same time, the PE two-layer structure also has a strong water absorption capacity, which can largely prevent the influence of moisture in the soil on the pipeline operation. The price of the PE two-layer structure is not high, so it is suitable for long-distance natural gas pipelines. It is very suitable, but in its practical application, there are also corresponding problems. On the one hand, such materials cannot be placed under the sun, otherwise, they will be seriously disturbed by ultraviolet rays and lose their protective effect. On the other hand, such materials are not easy to bond tightly to the pipe, so the protective effect will be greatly reduced. Finally, the PE three-layer structure. This kind of PE three-layer structure belongs to the pipeline protection measures produced, and it is also the most effective protection measure at this stage. Compared with the two-layer structure, the three-layer structure adds epoxy powder in the middle link, which not only realizes the improvement of corrosion resistance but also provides assistance for the close combination of the material and the pipeline, so that it can give full play to its protective performance. In addition, because the PE three-layer structure contains epoxy powder, the material will no longer be disturbed by ultraviolet rays and can be used in the sun.

(2) Electrochemical protection

In the actual electrochemical protection process of long-distance natural gas pipelines, the cathodic protection method of the sacrificial anode is often used. The principle of this chemical transmission pipeline anticorrosion method is very simple. In the actual application process, a metal material that is more active than the metal material used in the pipeline is added outside the transmission pipeline to form a galvanic battery. In this galvanic cell, the anode is the active metal and the cathode is the pipe, which will be protected during the actual corrosion phenomenon. In the actual application of such anti-corrosion measures, the length, wall thickness, and environment of the pipeline should be comprehensively considered. The location and weight of the active metal are then calculated in detail.

(3) Cathodic protection method of external power supply

In the actual application process, the anti-corrosion method of this transmission pipeline is applied less frequently, but it is theoretically feasible. In the actual application process, the power supply should be increased on the outer wall of the pipeline, so that the pipeline can be efficiently Protected. The reason for the relatively small number of applications is that most natural gas is a flammable and explosive gas. When using this method, it is also necessary to perform a simple calculation of the voltage according to the actual situation.

3. Common defects of cathodic protection of long-distance natural gas pipelines

After a long period of operation, many problems have arisen during the application of cathodic protection systems in long-distance natural gas pipelines. On the one hand, the cathodic protection equipment is old and aging, and can no longer operate normally. The reason for this problem is that the potentiostat adjustment switch at the first station of the long-distance natural gas pipeline fails due to the time problem, and the protection potential cannot be adjusted. The potentiostat converter at the last station cannot perform the efficient conversion, resulting in output from the machine, but no output from the pipeline. The high resistance of the anode ground bed has a great impact on the divergence of the cathode current, and the sacrifice of the anode cannot play its due role, which leads to the loss of protection of most of the pipelines and causes serious corrosion. On the other hand, the protection potential of the pipeline is too high, causing serious corrosion of some pipe sections. At this stage, the potential of most long-distance natural gas pipelines is in a high state, and the protection potential of the pipeline has deviated from the normal potential, which further aggravates the corrosion of the pipeline.

4. Countermeasures to improve the cathodic protection of long-distance natural gas pipelines

In the process of pipeline cathodic protection of natural gas, the first method to be selected is the pipeline cathodic protection method. Since long-distance natural gas pipelines usually use sacrificial anodes and forced current cathodic protection for pipeline anticorrosion, at this time, the buried depth of pipelines and sacrificial anodes is usually kept within the range of 2m to 2.5m, but for long-distance natural gas pipelines, In other words, its length is too long. At the same time, due to the natural landform, there is a serious drop between the two ends of many pipelines. At the same time, the groundwater level at both ends of the pipeline is different from the geological conditions, and the resistivity of the soil where some pipelines are located is too high. , the cathodic protection method using sacrificial anodes in this area is not very efficient. The solution to this problem is to change the sacrificial anode protection method to forced current protection for the high soil resistivity section of the long-distance pipeline. Law. Secondly, during the application of the forced current method, the potentiostat can provide continuously adjustable cathodic protection current to the metal body to be protected. It provides an auxiliary function for the anode in the forced amperometric method and is used to form a loop for the cathodic protection current provided by the potentiostat. Finally, in the actual cathodic protection process of long-distance natural gas pipelines, a professional team with a strong sense of responsibility can be created, and the principle of defining positions and responsibilities can be used for management. While improving the overall quality of the team, expanding the management field, and then improving our country. Cathodic protection of long-distance natural gas pipelines.




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