Mounting of expansion joints, sliding points and fixed points

The pressure in the line gives rise to forces that may lead to line instability if no sliding points and fixed points are provided. If movements occur in different directions inside a pipeline, these need to be divided by planning anchors at suitable intervals. If stable anchors are not possible, the expansion joints need to be mounted such that the axial movement is diverted and can be received by tied lateral expansion joints. The correct mounting of universal, lateral and angular expansion joints is crucial to the functionality of the entire pipeline system.

Pipeline systems should be fitted with ventilation equipment at high points and draining equipment at low points in order to avoid uncontrolled water ingress or vacuum. Pressure and vacuum safety mechanisms in the lines prevent the expansion joints from being overloaded. Likewise, the medium temperature should be monitored using appropriate means. Information about the maximum operating temperatures and pressures is specified based on the respective expansion joint types.

Fixed point

Sliding point

Guidance

Universal expansion joint

Lateral expansion joint

Angular expansion joint

Universal expansion joints for axial, lateral and angular movement

Expansion joint to receive axial movements along the pipeline axis. The fixed points receive the stresses from the active bellows cross-section of the expansion joint in the event of pressure or vacuum. In the event of large axial movements, the pipeline should be subdivided into several sections using sliding and fixed points.

Expansion joints to receive axial movements at a pipe outlet. The fixed points receive the stresses from the active bellows cross-sections of the expansion joints in the event of pressure or vacuum..

Expansion joint to assimilate axial and lateral movements at a pipe outlet. The sliding and fixed points receive the stresses from the active bellows cross-sections of the expansion joints in the event of pressure or vacuum.

Expansion joint to assimilate axial and lateral movements. The sliding and fixed points receive the stresses from the active bellows cross-section of the expansion joint in the event of pressure or vacuum.

Lateral expansion joints for lateral movement

Expansion joints to assimilate axial movements diverted into lateral movements. The tie rods receive the stresses from the active bellows cross-sections of the expansion joint in the event of pressure or vacuum.

Angular expansion joints for angular movement

Expansion joints to assimilate axial movements diverted into angular movements. The joints receive the stresses from the active bellows cross-sections of the expansion joints in the event of pressure or vacuum. The tie rods’ axes of rotation should be mounted vertically for axial movements.

Cardan joint expansion joints

Expansion joints to assimilate axial movements diverted into angular movements. The joints receive the stresses from the active bellows crosssections of the expansion joints in the event of pressure or vacuum.

Pressure balanced expansion joints

Expansion joints for the assimilation of axial movements without transferring stresses resulting from pressure or vacuum to the adjacent fixed points, apparatus or machines. The difference between the active bellows cross-sections of a large and small expansion joint corresponds to the active bellows cross-section surface area of a small expansion joint. If the tie rods are installed so that they intersect, the stresses will cancel each other out. Only axial forces of the expansion joints are induced in case of movements.

Expansion joints for the assimilation of axial movements in a pipeline elbow without transferring stresses resulting from pressure or vacuum to the adjacent fixed points. Corner-balanced expansion joints are used if only axial expansion is possible due to the course of the pipeline or due to lack of space, and when it is uneconomical to use a fixed point to accommodate the stresses. Only axial forces of the expansion joints are induced in case of movements. These are only axial forces for movements in direction of the expansion joint axis and only lateral forces for movements transverse to the expansion joint axis.

Expansion joints in the form of “dismantling joints”

In order to compensate for installation imprecision or to simplify connection and disconnection, tied expansion joints can be used. On the one hand, the tie rods prevent the transfer of stresses to the connected armature. On the other hand, after the flange connection is loosened using the tie rod flange, the rubber bellows can be compressed by its maximum potential axial movement capability in order to create clearance for dismantling of the armature.

Pump connection

Expansion joints are used to disconnect pumps from pipeline systems in order to avoid transferring forces, tensions and oscillations. We recommend installing expansion joints on the pressure side using tie rods in order to avoid transferring the expansion joint stresses to the pump connections. In the event of a vacuum exceeding 0.8 bar absolute on the vacuum side, a vacuum support ring should be used. The expansion joints should be installed as close as possible to the pump connections on both the pressure and vacuum sides.

For the transport of abrasive media (liquids containing solids), a distance of 1 to 1.5 x the nominal pipeline diameter should be maintained between the pump connections and the expansion joint. Bouncing and turbulence in the immediate vicinity of the pump connection may damage the expansion joint. This also applies when expansion joints are mounted in the vicinity of elbows and outlets. Also note that expansion joints in the vicinity of flap gates or slide valves that are only partly closed may be destroyed. Pump cavitation may also lead to sudden expansion joint failure.

Expansion joint presetting

In order to increase axial movement, the expansion joint can be presetted to its maximum extension during installation. For expansion joints with swivel flange there is a risk during the extension that the sealing bulge will spring from the groove of the backing flange. If presettings of more than 10 mm are needed, a flange connection will need to be disconnected at another location. Now the expansion joint can be installed relaxed and the flange disconnection sites that were opened before can be closed again.

In order to increase lateral movement, the expansion joint can be presetted to its maximum lateral displacement against the direction of movement during installation. During operation, it will move back to the opposite side through the zero point. In this way, the lateral movement can be increased by up to 100%. For expansion joints with swivel flange there is a risk during displacement that the sealing bulge will spring from the groove of the backing flange. If presettings of more than 5 mm are needed, a flange connection will need to be disconnected at another location. Now the expansion joint can be installed relaxed and the flange disconnection sites that were opened before can be closed again.