The basic element of an expansion joint is the bellows a flexible, corrugated tubular metal element to absorb movements in a piping system.

In the operating environment the critical stresses and movements may act in axial, lateral or angular directions and the bellows must therefore be designed and dimensioned to accommodate these movements.

Special designs are documented by means of Finite Element Analysis (FEA), a 3D technique that provides a high degree of documentation and detailing and to predict how a structure or assembly will react to forces caused by heat, vibration, mechanical stress in operating conditions.