Categories, Applications and Selection of Expansion Joints (Part One)

An expansion joint consists of a bellows (a kind of elastic element), a bracket, a flange and connectors at both ends, which is also a kind of compensating component. An expansion joint uses effective deformation of its bellows to compensate expansion and contraction of a pipeline and a vessel caused by heat and cold due to temperature variation. An expansion joint can be used for compensating axial, lateral and angular displacement of a pipeline and a vessel, and it can also be used for reducing noise and vibration, which make an expansion joint widely used in modern industry. When temperature goes up in heat supply pipelines, the expansion joint should be installed on the pipeline in order to prevent the pipeline being deformed or destroyed due to expansion caused by heat or temperature stress. The expansion joint can compensate expansion caused by heat so as to reduce stress of walls of pipes and acting force on valves and brackets. As an important part for pipework, the expansion joint plays an important role in ensuring the long-term normal operation of the pipeline.

Tips for selecting expansion joints
Expansion joints have rectangular sections and waveform with the same shape. A single expansion joint in the pipe bears two-dimensional displacement. The pipeline consisting of two expansion joints can bear three-dimensional displacement. Metal expansion joints can be classified into full-height expansion joints and half-height expansion joints.

1. After the user select the appropriate expansion joint according to the thermal displacement of the piping system, they need to provide information about the medium in the pipe, design pressure of the duct, the highest temperature during operation, the overall dimension of sections of the duct, the selected waveform and the number of the waveform so as to design and manufacture structure of expansion joints.

2. The maximum allowable expansion of each waveform 
Full-height type: △α = ± 24 mm  Half-height: △α = ± 12 mm.

3. The ash board: For pipes with less dust, the ash board doesn’t need to be used; for flue pipes with much dust, the ash board should be adopted.

4. In order to reduce the number of the waveform, we should consider the cold-drawn process for expansion joints.

5. Expansion joints are suitable for pipes whose cross-sectional areas are less than 4.6 square meters and one side of the overall dimension of the air and flue gas duct which is less than 1.5m but greater than 0.6 mm. Standard full-height expansion joints can be applied to all air and flue gas ducts.