The main pipes for buried gas pipelines are cast iron pipes, PE pipes, and steel pipes. The nature of each pipe determines the strength, plasticity and corrosion resistance of the pipeline. Therefore, choose suitable pipes based on research on the use environment and characteristics of the pipeline's materials, analyzing the cause of leakage of pipelines on the premise of safe performance, so that the effective running time of the pipe is increased, and the leakage rate of the pipeline and the construction cost can be reduced.
1. Reasons for leakages of gas pipelines
Generally speaking, we divide the running time of pipelines into the early stage, the middle stage, and the late stage. The early stage is the trial operation period after the completion of the construction. Some problems will appear for the pipeline concerning materials, design, and construction, resulting in leakages of pipelines. Meanwhile, during the trial operation, the improper operation of operators will also increase the probability of the leakage of the pipeline in the initial stage. In the middle stage of the operation of pipelines, that is, the pipeline has been operating for 2 to 8 years. If the pipeline is not damaged by external forces, it will be able to maintain a low probability of accidents caused by leakages. In the later stage of the operation of pipelines, the pipeline is easier to break due to corrosion damage of soil and other external environments, causing the accident rate to increase.
In the 1970s, the International Pipeline Research Association of the United States first evaluated the risk of oil and gas pipelines by drawing lessons from the risk analysis technology in economics and other industrial fields. They analyzed and classified the accident data of gas pipelines in the United States and Europe and 22 kinds of basic factors for the failure of pipelines were summarized.
Geological disasters generally refer to phenomena such as earthquakes, landslides, and geological subsidence caused by crustal movement. In the environment of cities and towns, geological subsidence is more common. Because the land subsidence will cause the pipeline to be subjected to external stresses, these external stresses will accelerate the damage to the fragile part of the pipeline. If the strength of the pipeline is not enough, it will also cause the fracture of the pipeline. The main reason for the fatigue fracture is the external stress on the pipeline, which causes the metal to deform repeatedly and increases the risk of fracture. Corrosion, cracks and manufacturing defects depend on the composition of the pipe's material. The different internal organizational structure of the pipe's material will not only affect the corrosion resistance of the pipe, but also influence the formation of cracks in the welding process. Therefore, when manufacturing the pipe, we should avoid the inclusion of impurities and other metal elements as much as possible to improve the purity of the material. Prevent the damage caused by the third party. Choose pipes with high strength can reduce the damage caused by the third party to a certain extent.
2. Data statistics of outdoor gas accidents
The use of gas brings us great convenience in our lives, but it also has certain hazards. Besides the safety of indoor pipelines, we should also pay attention to damage caused by the third party for outdoor gas pipelines and aging of pipelines for operating units. According to media statistics, a total of 722 gas explosion accidents occurred from January to December in 2019. There were 256 outdoor gas accidents, accounting for about 35.46%. Among the 259 accidents, the cause of the leakage in 204 cases could be conformed, among which 169 accidents were caused by external forces on the gas pipeline. Therefore, it can be seen that the probability of accidents caused by external damage to the pipeline is high. From the analysis of the reasons, gas companies should further strengthen inspections of pipelines and construction cooperation and supervision of external accidents. The government should further strengthen the protection of gas pipelines. For example, the pre-conditions for permits of underground municipal engineering construction must be that the company verifies the conditions of underground gas pipelines in the region.
Figure 1 Statistics of monthly gas accidents reported by national media in 2019
Figure 2 Reports on the causes of outdoor gas accidents by national media in 2019
Figure 3 Reports on the causes of outdoor gas accidents by national media in 2019
It can be seen from the statistics of the causes of outdoor gas accidents that the safety problems of outdoor pipelines mainly focus on the following aspects: damage caused by the third party, corrosion of pipelines, foundation collapse, crushing by the external force, leakages of flanges and other joints. According to the requirement for the pipe's material, the above reasons for leakages are related to the hardness, toughness and corrosion resistance of the pipe as well as the connection strength of the welding part.
