Central heating has become the main way to solve the problem of heating in medium, large and super-large cities in China. Compared with foreign countries, although the development of central heating in China is relatively late, it has developed rapidly in recent years, and has the characteristics of large pipe diameter and long transmission distance. At present, the laying mode of thermal insulation pipeline network in China is mainly directly buried. However, due to the interaction of material aging, environmental corrosion, extreme load and other conditions, the structural state degradation of directly buried heating pipeline is inevitable, and even the safety accident of pipeline leakage occurs. Pipeline leakage not only causes huge direct and indirect economic losses, but also has a serious impact on people's lives and public safety. Therefore, the safety monitoring, evaluation and early warning technology of directly buried thermal insulation pipeline has become the focus of research.
The primary stress is the main factor affecting the structural safety of directly buried heating and insulation pipelines, while the bending stress caused by overlying soil load and uneven settlement is the main form of primary stress. At present, there is no effective method to monitor the primary stress of directly buried heating pipelines.
In view of the difficulty in quantifying the bending strain of the working pipe of the directly buried thermal insulation pipeline in practical engineering, a method for monitoring the structural state of the heating pipeline based on distributed optical fiber sensor is proposed. The monitoring system includes sensor unit, data acquisition unit and remote data transmission unit. Distributed fiber optic strain sensor and distributed fiber optic temperature sensor are arranged between insulation layer and outer protective tube to realize remote real-time monitoring of bending strain and leakage behavior of working tube. The monitoring of a directly buried heating pipe section under backfilling construction is carried out.
Distributed optical fiber temperature sensor can truly measure the temperature distribution along the pipeline. Distributed optical fiber strain sensor can effectively monitor the bending strain of the working pipe. Monitoring data show that the bending stress of insulating pipes caused by overlying soil load, uneven groove foundation and uneven settlement is very significant. As a primary stress, it is very important for the safety of pipelines. Ignoring the primary stress related to bending behavior in the safety assessment of heating pipes will lead to unsafe results. It is necessary to implement distributed real-time monitoring for directly buried thermal insulation pipelines.