Thermal expansion and cold contraction of thermal pipeline is a common phenomenon in engineering, but the key to design is to fundamentally reduce the stress caused by thermal expansion and cold contraction. The thermal pipes in the project are compensated by self bending according to the layout characteristics of the pipes. If this method can not eliminate the stress of the pipes, it needs to be solved by adding compensators on the pipes. In this paper, the common methods to eliminate the stress of the heat pipe and the characteristics of the compensator are described. Through the flexible analysis of the heat pipe, the safety and stability of the heat pipe are ensured.
Heat pipes are common in life and production. However, heat pipes have long transmission distance and high temperature of transmission medium. In the process of pipeline transmission, pipeline fracture and medium leakage may occur due to excessive pipeline stress, causing personal injury to operators or surrounding residents, and also causing loss of state property to a certain extent. Therefore, the design of thermal pipeline must pay attention to the problem of thermal expansion and cold contraction. In order to ensure the stable and safe operation of the pipeline under the thermal state and reduce the stress generated during the thermal expansion and cold contraction of the pipeline, it is necessary to consider compensation measures for the thermal elongation when the pipeline is heated.
1. Calculation of pipe elongation
The elongation of the thermal pipe is equal to the difference between its installation temperature and the medium design temperature multiplied by the pipe length multiplied by the linear expansion coefficient of the pipe material.
The formula is as follows:
△L=Lα（t2-t1）
2. Principle of pipeline thermal compensation
First, natural compensation shall be considered according to pipeline layout requirements; Secondly, the elastic deformation applied to the pipeline in advance when installing the pipeline to generate the expected initial displacement and stress; When the above two conditions fail to meet the requirements for thermal elongation compensation of the pipeline, a compensator must be used; When selecting the compensator, the compensator shall be selected according to the pipeline layout and space requirements; The installation position of the compensator shall ensure that the pipeline layout is beautiful and coordinated.
3. Method of pipeline thermal compensation
3.1 NATURAL COMPENSATION
Natural compensation is that the thermal pipeline absorbs the thermal deformation of the pipeline by using the elasticity of the natural bending of the pipeline itself. Pipeline elasticity refers to the ability of the pipeline to recover its original state after the elastic deformation, geometric shape change and stress disappear under the action of stress. Practice has proved that when the bend angle is greater than 30 °, it can be used as natural compensation; when the bend angle is less than 30 °, it cannot be used as natural compensation. The natural compensation pipeline length is generally 15-25m, and the bending stress б BW shall not exceed 80MPa. Natural compensation commonly used in thermal pipeline engineering includes L-type compensation, Z-type compensation and space three-dimensional bending.
3.2 THERMAL COMPENSATION
If the natural compensation of the heating pipeline cannot be satisfied, a compensator shall be added to the pipeline to compensate the thermal deformation of the pipeline. The compensator is an element arranged on the pipeline to absorb the thermal expansion, cold contraction and other displacements of the pipeline. The commonly used compensators are square compensators, bellows compensators, sleeve compensators and spherical compensators.
- In the actual thermal pipeline construction, because the square compensator is easy to install and disassemble, its safety factor is relatively reliable, its service life is long, and the maintenance times in the later period are not very high. Therefore, in actual use, the frequency is high. Unless there are special circumstances, the on-site construction personnel will use other compensators. This type of compensator is made by a special process. Its principle is that after the U-bend is made, it absorbs the heat inside the pipe and deforms to compensate the pipe stress. The main compensation method is also realized by bending deformation. In terms of composition, the square compensator is mainly composed of horizontal, telescopic and free arm, with simple structure. Unfortunately, the square compensator lacks aesthetic appearance and occupies a large space.
- Secondly, the structure of bellows compensator is similar to that of square compensator, which is also very simple. Its later maintenance cost is not high, and its frequency of use is second only to square compensator. Constructed with one or more bellows and other fittings. The main working principle of bellows compensator is to compensate for the size change of pipeline equipment through its own deformation. In the actual construction process, the deformation compensation amount of such compensators shall not be less than 50%. In addition, in terms of installation, only one set of compensator can be installed between two fixed supports. The installation position and support point of the fixed frame also have high requirements, which shall be clearly indicated in the engineering drawings.
- The third type is sleeve type compensator, which is mainly composed of pipe sleeve, cannula and sealing filler. It is also called packing type compensator for this reason. The installation environment is also mostly outdoor, and the compensation method is different from the above two compensators, which mainly compensates for the variable by the relative movement of the cannula and the pipe sleeve. The pipe sleeve type compensator is also divided into iron pipe and steel pipe type compensator according to the different appearance materials. Compared with the square compensator, the type of this paragraph occupies less space, has greater compensation capacity, and is very convenient for installation. However, its disadvantages are more obvious. When the compensator moves axially, there is a risk of leakage. Once leakage occurs, the pipe sleeve and the internal filling material must be replaced. In addition, the external pipe sleeve is also prone to the risk of ferrule. Therefore, the later maintenance times are more than the former two compensators.
- Fourth, spherical compensator. The structure is mainly composed of spheres, sealing devices and other elements. After being installed on the manual pipeline, the movable spherical part of the compensator is used to make an angular turn to compensate the thermal deformation of the pipeline, so as to reduce the pipeline stress. It allows the pipe to rotate relatively within a certain range, so the two straight pipes can not be kept in a straight line. The advantages of the spherical compensator are: large compensation capacity, small occupied space, small fluid resistance, convenient installation and low investment.
4. Conclusion
The thermal pipeline solves the problem of thermal stress through natural compensation and thermal compensation to a great extent, and ensures the stable and safe operation of the thermal pipeline. In the selection of compensator form, it is necessary to make reasonable selection according to local conditions and combined with the characteristics of the pipeline and the different advantages and disadvantages of the compensator, so as to better ensure the flexibility of the thermal pipeline.
(Hunan Great is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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Post time: Aug-24-2022