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Thermal expansion coefficient

 

     Today we focus on thermal expansion coefficient subject. In boilers met in Energy sector thermal expansion arise in many structures. Generally for rule expansion should not be blocked. The exception is when it is difficult to avoid. The purpose of it is to eliminate thermal stress. Thus structures are constructed in such way that they can expand freely. Where it is needed extra flexibility is applied on purpose to compensate thermal expansion. Such solutions are used for piping, coils, air and flue gas ducts. Sometimes thermal expansion is blocked in natural way by structure alone, but we discuss it further.

Thermal expansion can be calculated as follow: 

ΔL = α·L, where:

α - expansion coefficient [mm/m], L - analized structure length [m]

 

Let's focus at simply supported beam. In case of beam temperature growing, it can expand freely.

Free expansion

  

Now look at fixed beam with thermal load. It is presented below:

 Beam thermal expansion

Expansion is blocked due to fixing at both ends. Internal forces appear.

 

In case of piping the most popular solution for getting flexibility is suitable piping routing. Bends, loops and routing type "Z" are used to redistribute thermal movements.  It is presented visually at picture below.

piping flexibility

to be continued.

I encourage to download program to expansion coefficient calculations: 

Thermal expansion coefficient