Shell and heat exchangers serve as process coolers. It means they often need an expansion bellows to reduce stresses in vital exchanger elements. Therefore, it’s crucial to consider various factors when creating an affordable expansion bellow design. Doing this will help ensure the safety of operations and reliability. Being keen on details and working with the welder from the start to the end can make a lot of difference. It will determine if you will experience sudden failure or a long-lasting operating life. So, what’s the role of the expansion bellows or joints in shell-and-tube heat exchangers?
What’s an expansion bellow?
It is also known as an expansion joint or movement joint. It’s a fabrication made to clutch components together while absorbing temperature-induced expansions and contractions of building materials and vibration. Commonly found in shell and tube heat exchangers, railway tracks, piping systems, buildings, e.t.c. But, before going to the role they play, here are the types of these joints.
Types of expansion bellows
There are two types: Flanged and flued and the below.
– Flanged and flued
It’s as thick as the shell and made of the same material. Its shape adds axial flexibility to the shell-making processes in equipment companies. The main con of this joint is durability, meaning it’s less likely to fail.
– Bellow type
These joints are thinner and have several formed convolutions like an accordion. They are welded to the adjacent shell, and their main advantage is flexibility. Bellows are best for large thermal expansion to help relieve stress in a huge differential temperature exchanger.
However, due to their thin walls, they are easily damaged during service and should be protected with a metal shroud. They can be made of other materials, but alloy 625 is the most common. The reason is its resistance to corrosion, strength and flexibility. Other materials and stainless steel can be used depending on the equipment company’s processes and design requirements.
Why are expansion bellows or joints needed in shell-and-tube heat exchangers?
The main function of shell-and-tube heat exchangers is to utilize one fluid to heat the other without mixing them. In these heat exchangers, one fluid passes inside tubes and the other through the shell side. For these two to exchange heat, there must be a variation in their temperatures.
Example
In chemical processes, the exchangers are used to regulate the temperatures. First, the hot chemical runs through the tubes and cools water on the shell side. Then heat is transferred from the chemical streaming to the tube wall on the shell side of the exchanger. Always remember that the components of the exchanger cause the differential temperature. It means that the tube and shell expand or contract at varying rates.
Here the exchangers act as process cooers where the shell is cooled by the water and does not thermally expand. However, the tubes are in touch with the hot chemical process. So, they will increase in length due to the high temperatures. The best way to relieve the stresses in critical exchanger elements is by adding an expansion joint in the shell. The expansion bellow allows the exchanger shell to change length and maintain strength to resist internal pressure.
Shell and tube exchangers mostly serve as process coolers. During the process, thermal expansion occurs, which can cause stress to the shell. Most companies use expansion joints to maintain strength and resist internal pressure.
