Hinged Expansion Joints
When the angular movement is only in one plane hinge or angular expansion joints are used. An angular expansion can be expressed when an expansion joint experience bending about its center which is the centerline and half way between the ends of metal bellows.
These types of bellows are used mostly in sets wherever piping direction changes. So you will find hinged joints used at the locations where pipe bending occurs. Due to the hinged nature of this bellow only angular movement is allowed around the hinges. Since lateral movements too take place so there is a piping joint between these 2 bellows. The amount of lateral deflection a hinged expansion joint can accommodate for a given angular movement is directly proportional to the distance between them. To use a pair of hinged bellows effectively the distance between them should be made as large as possible. When only two hinge joints are used as shown in the adjacent figure the piping perpendicular to the hinge segment must deflect to absorb the thermal expansion of the spool containing these angular expansion joints.
When the piping in a single plane system is not flexible enough to absorb the thermal expansion of the spool between the hinged joints a system of three hinged expansion joints may be used. In this system the combination of the three joints absorbs all the thermal expansion of the piping system and no deflection of the piping is observed. This system produces the lowest possible forces on the intermediate anchors and guides
If the thermal growth in the Piping System occurs in only one plane the use of this joint provides the most efficient solution to absorb the thermal deflections.