Anti-corrosion Measures for Long-distance Natural Gas Steel Pipelines

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

(1) Addition of coating. The main methods of adding coating 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 steel pipeline from being affected by stray currents, which plays a very critical role in the protection of the steel 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 on the temperature of steel pipelines. Once the temperature of the conveying steel pipeline exceeds the regulations of coal tar enamel The temperature will cause the melting of coal tar enamel, which not only fails to protect the steel pipeline but also may cause environmental pollution, which in turn cannot protect the steel pipeline. Therefore, in the actual application process, it should be noted that coal tar enamel is not suitable for heating and conveying steel pipes. 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 steel pipeline is also a steel 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. The bacterial interference can play 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 water in the soil from affecting the operation of the steel pipeline. In terms of Taoism, it is very suitable, but there are corresponding problems in its practical application. On the other hand, such materials are not easy to bond tightly with steel pipes, so the protective effect will be greatly reduced.

Finally, the PE three-layer structure. This kind of PE three-layer structure belongs to the protection measures of the steel pipes 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 achieves the improvement of corrosion resistance but also provides assistance for the close combination of the material and the steel pipe, so that it can fully exert 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 steel pipelines, the cathodic protection method of the sacrificial anode is often used. The principle of this chemical transmission steel pipeline anticorrosion method is very simple. In the actual application process, a metal material more active than the metal material used in the steel pipeline is added outside the transmission steel pipeline to form a primary battery. In this galvanic cell, the anode is the active metal and the cathode is the steel 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 steel pipeline should be comprehensively considered. The location and weight of the active metal are then calculated in detail.

(3) Cathodic protection method with external power supply. In the actual application process, this anti-corrosion method for transmission steel pipelines is applied less frequently, but it is theoretically feasible. The power supply is increased on the outer wall so that the steel pipe can be effectively 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.