Common defects and countermeasures in anticorrosion and cathodic protection of long distance natural gas pipelines

Finally, PE three-layer structure. This PE three-layer structure is the latest pipeline protection measure, 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 improves the corrosion resistance, but also provides help for the tight combination of the material and the pipe, so that it gives full play to its protective performance. In addition, due to the epoxy powder contained in the PE three-layer structure, the material will no longer be disturbed by ultraviolet light and can be used in sunlight.

(2) Electrochemical protection

Cathodic protection with sacrificial anode is often used in the actual electrochemical protection process of long-distance natural gas pipelines. The principle of this chemical transmission pipeline anticorrosion method is very simple, in the actual application process, a metal material is added outside the transmission pipeline that is more active than the metal material used in the pipeline, and then the galvanic cell is formed. In this primary 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 of the pipeline, the wall thickness and the environment in which it is located should be considered comprehensively. Then the position and weight of the active metal are calculated in detail.

(3) cathode protection of external power supply

In the actual application process, this transmission pipeline anticorrosion method is applied less times, but in theory is feasible, in the actual application process, should be in the outer wall of the pipeline to increase the power supply, so that the pipeline is effectively protected. The reason for the relatively small number of applications is that most natural gas is flammable and explosive gas, and when using this method, it is also necessary to perform a simple voltage calculation according to the actual situation.

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

After running for a long time, many problems arise in the application process of cathodic protection system for long distance natural gas pipeline. On the one hand, the cathodic protection equipment is old and aging, and it can no longer operate normally. The reasons for this problem are: Due to the time problem, the potentiostat regulating switch at the first station of the long distance natural gas pipeline failed to adjust the protection potential, and the potentiostat converter at the final station could not be converted efficiently, resulting in output of the machine but no output of 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 can not play its due role, which leads to the loss of protection of most of the pipes, resulting in serious corrosion. On the other hand, the pipeline protection potential is high, which causes serious corrosion of some pipe sections. At present, the potential of most long-distance natural gas pipelines is in a higher state, and the pipeline protection potential deviates from the normal potential, which further intensifies the pipeline corrosion.

4. Improve the countermeasures of cathodic protection for long-distance natural gas pipelines

In the process of pipeline cathodic protection of natural gas, the first method to be selected is pipeline cathodic protection. Because the long-distance natural gas pipeline usually uses the sacrificial anode and the cathodic protection law of forced current to prevent corrosion of the pipeline, at this time, the buried depth of the pipeline and the sacrificial anode is usually maintained in the range of 2m ~ 2.5m, but for the long-distance natural gas pipeline, the length is too long. At the same time, due to the reasons of natural landform, the two ends of many pipelines have a serious gap. At the same time, the groundwater level at both ends of the pipeline is different from the geological condition, and the resistivity of the soil where some pipelines are located is too high, so the efficiency of cathodic protection with sacrificial anode is not high in such areas. The solution to this problem is to change the sacrificial anode protection law to forced current protection law for pipelines with high soil resistivity during the process of long distance pipeline. Secondly, in the application of forced current method, potentiostat can provide continuous adjustable cathodic protection current to the metal body to be protected. The anode in the forced current method is assisted to loop the cathodic protection current provided by the potentiostat. Finally, in the actual process of cathodic protection of long-distance natural gas pipelines, we can create a professional team with a strong sense of responsibility, and adopt the principle of fixed post and responsibility for management, while improving the overall quality of the team, expand the management field, and then improve the cathodic protection of China's long-distance natural gas pipelines.