We often see a scene like this on steam pipes, that is, the pipe section that can be straight suddenly bends. I believe that many people who have seen this will have the same doubt as me. Isn't this superfluous? As a matter of fact, it is not. The design of pipeline operation has its own principle. Let me make you understand the function of a bend for a steam pipe.
 
The steam pipeline has two working states. One is in the high temperature, and another is close to the ambient temperature. In the alternating cold and heat, displacement and stress will occur due to the principle of expansion caused by heat and contraction caused by cold. The longer the pipeline is, the greater the displacement and force become. Measures need to be taken to avoid damage to the pipeline, so a bend which is also called an expansion joint is adopted. An expansion joint is used to absorb the axial expansion and displacement of the pipe and can also avoid concrete beam columns.
 
China has relevant regulations for expansion joints, such as Article 4.8.17 of Design Specifications for Heating, Ventilation and Air Conditioning Planning.Thermal expansion of heating pipes must be calculated. When the natural compensation of the pipe section cannot meet the requirement, a compensator should be installed. The power chemical design specification also has such requirement, and some even require a software to be used for calculation. For example, power plant design institutes generally use GLIF, and chemical design institutes generally use Caesar.
 
The compensation amount must be calculated before installation. The installation process requires cold drawing, especially the main steam outlet. The bracket is also important. The sliding and fixed brackets are mainly tested, and the natural compensation should be used as much as possible in the factory.

So how long is the expansion of the pipeline? According to test calculations, for a distance of one meter, when the temperature increase 100 degrees, the expansion is about 1.2mm. In some industries like power plants, the temperature rise can reach more than 500 to 600 degrees. At this time, expansion for one meter is about 7 to 8mm. Metal is a stretchable but incompressible material. Imagine that the rail has a temperature difference of 50 degrees at ambient temperature. The early rails still had a protruding situation. Later, segmented rails were used to solve this problem. However, the pipeline is often hundreds of meters or even tens of kilometers, and the change in the cold state and hot state will cause great stress. If the stress exceeds the limit of the pipeline, the pipeline can’t naturally bear it and may cause serious consequences.
                
When natural compensation cannot meet the requirement for the pipeline, we usually use a compensator for compensation, which can absorb the axial, lateral and angular cold and heat deformation of the pipeline, and reduce the impact of equipment vibration on the pipeline. The role of the U-shaped section on the steam pipe is similar to this.