What is an Axial Expansion Joint?
Axial Expansion Joints are the simplest type of expansion joints using a single bellows unit. Stainless steel expansion joints are compact requiring virtually no additional space beyond the length of bellows and weld ends or flanges for installation. These Axial Expansion Joints have a further advantage of not imposing a change in the direction of flow. Where small thermal movements are involved and where proper anchoring and guiding are possible, single axial bellows provide the most economical solution.
INTERMEDIATE ANCHOR ARRANGEMENT FOR OPPOSITE MOVEMENT
ANCHOR & GUIDE SPACING ARRANGEMENTS FOR AXIAL BELLOWS
The most common application of axial expansion joints is to absorb axial movements of a straight pipe between main anchors. These single expansion joints should be placed near one anchor and guides should be utilized to ensure proper alignment and movement control as shown in the adjacent figure.
Various Types of Axial / Single Expansion Joints
Fixed Flanges Compact
Under pressure, this joint exerts a reaction force on the adjoining pipe. This reaction force should be absorbed by anchors at both ends of the pipe section in which the axial expansion joint is installed. In a piping system with several expansion joints, the system should be broken up by intermediate anchors into sections with one such 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.
ANCHOR & GUIDE ARRANGEMENT FOR T JUNCTION
TIED SINGLE EXPANSION JOINT FOR SMALL LATERAL MOVEMENTS
Stainless steel bellows are designed to compensate for axial displacements. Slight lateral movements of bellows are acceptable but reduce the cyclic life expectancy if the allowable axial movement is used at the same time. The lateral movement on this type of expansion joint produces the highest forces and the most detrimental movement for this type of expansion joint. For this reason, axial expansion joints should be installed co-axially with the piping. The Stainless steel bellows should be made to avoid lateral movements by providing directional main anchors at the ends (two-direction supports acting at right angles to the axis of the pipe) to direct the piping growth into this joint only in the axial direction.
THIS REACTION FORCE = (MEAN EFFECTIVE AREA) X (LINE PRESSURE)
When the axial movements of the piping run exceeds the capacity of a single bellows axial expansion joint a double bellows joint with support foot ( intermediate anchor) welded to a center spool can be used.This type of double bellows axial expansion joint is located in the center of the piping run and each single joint on either side absorbs the axial movement of that section of the piping within which it is located.
ANCHOR AND GUIDE ARRANGEMENTS FOR CHANGE IN FLOW DIRECTION
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- Simple and most economical type of Expansion Joint with single bellows unit
- No change in for direction required.
- Compact requiring minimum space for Installation.
- Available in a single bellows or Universal Design.
- Economical Construction.
- Will not absorb pressure thrust unless tie rods are used.
- Strong anchors required.
- Pipe guides essential to direct the movement.
- Several Axial/Single Expansion Joints are required for large movements.
- Several anchors and guides required for long run pipe sections.