In the design and construction of direct buried laying must really understand the heating pipe is divided into direct buried laying and direct buried laying without expansion, both methods have their own characteristics and two methods, design a reasonable choice and construction of the working principle of the direct buried insulation pipe is safe, reliable and economical.
Direct buried insulation pipe laying has compensation: through natural compensation and compensators (such as square compensators and bellows compensators), the thermal stress is minimized. There is no compensation for direct embedding, which simply means that there is no compensation for the heat in the pipeline, but thermal stress absorption.
There is no need to compensate the installation and installation of the directly buried and directly buried insulation pipe. After the heat pipe is fixed to a certain temperature, the fixed pipe is welded. When the pipe returns to temperature (low temperature), the pipe is carried out in advance under the action of tensile stress. When working through the heat pipe, the pipe stress is zero as the temperature increases. When the temperature continues to rise, the compressive stress increases. When the temperature reaches the working temperature, the compressive stress and thermal stress of the pipe are still less than the allowable stress. In this way, the pipeline can work without compensating the equipment.
The fourth strength theory requires the compensation method of preheating pipeline construction, which will be very troublesome in the construction. There are also many engineering practices at home and abroad. The theoretical calculation is reliable and can guarantee the safety. In recent years, the classification of the thermal design institute of coal gasification in Beijing, China has been analyzed and the application of the third strength theory method and stress. The method gives full play to the plastic potential of steel, which is convenient for construction and not preheating.
Two different burial depth considerations: direct burial installation and deployment, embedding depth to determine the compensation, only considering that the stability of the pipeline will not be damaged may be due to the ground load, from the economic perspective, construction convenience, methods to be buried in direct burial compensation as shallow as possible. The thickness of the overlying strata shall be greater than 0.6 m, regardless of pipe diameter.
When there is no compensation for direct burial, the buried depth of the pipeline considering the stability of the requirements, general soil cover thickness, burial depth, stability, than the use of compensation for direct burial without preheating and compensation circuit, minimum soil cover depth should be rules and urban heat network design code (cjj34-90), the first soil cover thickness 7.2.15 implementation, is proportional to the diameter.
