Axial metal expansion joints are the simplest type of metal expansion joints. They are compact requiring virtually no additional space beyond the length of bellows and weld ends or flanges for installation. They have further advantage of not imposing a change in the direction of flow. Where small thermal movements are involved and where proper anchoring and guiding is possible single axial bellows provide the most economical solution.
The most common application for a single axial bellows expansion joints is to absorb axial movements of a straight pipe between main anchors. This axial bellows expansion joint should be placed near one anchor and guides should be utilized to ensure proper alignment and movement control.
Under pressure, single bellows expansion joint exerts a reaction force on the adjoining pipe. The force is calculated as: (Mean Effective Area) x (Line pressure)
This reaction force should be absorbed by anchors at both ends of the pipe section in which this expansion joint is installed. In a piping system with several expansion joints the system should be broken up by intermediate anchors into sections with an single bellows expansion joint in each section. The anchors at the end of the piping system are designed to absorb the full reaction force (pressure thrust force) of the expansion joints. Intermediate anchors are designed to resist forces due to friction, uneven cooling etc.
When the axial movements of the piping run exceeds the capacity of a single bellow expansion joint, a double joint with support foot ( intermediate anchor) welded to a centre spool can be used. This type of double bellows axial expansion joint is located in the centre of the piping run and each single joint on either side absorbs the axial movement of the section of the piping within which it is located.