Metal Expansion Joint
RADCOFLEX: Metal Expansion Joint
Radcoflex products are used extensively throughout many industries for a wide variety of applications including the conveying of materials and gases, mechanical protection, pipeline movement control and vibration
Metal Expansion Joint
A metal bellows expansion joint is a fabricated item to be fitted into a pipeline to absorb movements in and forces exerted on the pipeline. The joint consists of a metal bellows element with flanges or pipe weld ends fitted to facilitate the bolting or welding of the joint into a pipeline. Control devices, commonly called hardware in the industry, can be attached to control the direction and amounts of movement that the expansion joint achieves.A metal bellows expansion joint can be fabricated to accommodate axial, lateral or angular movements. Angular movement is the least severe on the bellows element of the three and laterals the most severe.
Technical Aspects
Construction
A metal bellows expansion joint is a fabricated item to be fitted into a pipeline to absorb movements in and forces exerted on the pipeline. The joint consists of a metal bellows element with flanges or pipe weld ends fitted to facilitate the bolting or welding of the joint into a pipeline. Control devices, commonly called hardware in the industry, can be attached to control the direction and amounts of movement that the expansion joint achieves.
Types of movement
A metal bellows expansion joint can be fabricated to accommodate axial, lateral or angular movements. Angular movement is the least severe on the bellows element of the three and laterals the most severe.Control devices would generally be required to be fitted to the joint where these movements occur concurrently.
Fatigue life
The fatigue life of an expansion joint can be defined as the total number of complete cycles which can be expected from the expansion joint based on data tabulated from tests performed at room temperature. A cycle can be defined as one complete movement of the joint from its initial position to its moved position and back again.
The fatigue life of an expansion joint is affected by a number of factors including:
- the operating pressure – the operating temperature
- the bellows material used – the thickness of the bellows material
- the movement required per convolution
- the height, shape and pitch of the convolutions
- bellows heat treatment requirements
A change in any of these factors will change the life of the expansion joint.
The standard Radcoflex catalogue listed expansion joints (with the exception of the externally pressurized AXI – line joints) have an expected life of 5000 full cycles.
Axial Movement Joints (FF - Flanged, WW - Pipe Weld Ends)
Product code
Type XFF – flanges both ends
Type XWW – pipe weld ends both ends
Type XFW – flange one end, weld end the other
Movement capability–Suitable for Large axial movements up to 200mm
Bore size range– standard 25 – 900mm
Pressure rating– standard joints 10, 20 and 40 bars – subject to pressure capability of attached hardware
Pipework system notes
Joint needs to be properly guided and anchored however since the joint has an integral pipe liner guide, it requires less guides than an internally pressurized joint.
Lateral Movement Joints
Product code
Type TUFF – flanges both ends
Type TUWW – pipe weld ends both ends
Type TUFW – flange one end, weld end the other
Movement capability–Suitable for Large lateral movements controlled by the tie rods
Bore size range– standard 50 – 1500mm
Pressure rating– standard joints4, 10 and 20 bars – subject to pressure capability of attached hardware
Pipework system notes–Tie rod hardware is attached to contain pressure thrust forces and in many cases main anchors are not required
Alternate selections–This joint is a low cost alternative to hinged and gimbal joints but should only be used where precise control of movements is not necessary
Angular Movement Joints
Product code
Type HFF – flanges both ends
Type HWW – pipe weld ends both ends
Type HFW – flange one end, weld end the other
Movement capability–Suitable for Angular movement in one plane onlycontrolled by the hinge
Bore size range– standard50 – 1500mm
Pressure rating– standard joints 4, 10 and 20 bars – subject to pressure capability of attached hardware
Pipework system notes–Hinge hardware is attached to contain pressure thrust forces and in many cases support the dead weight of the adjacent pipework. Heavy expensive main anchors are usually then not required.Single hinged joints are generally used in pairs with connecting pipework between, to act in unison to absorb large amounts of lateral movement at high pressures with minimum guiding requirements and very low stresses on attached piping.
Pressure Balanced Joints
Description
Two metal bellows elements – acting as flow and balancing bellows – connected by elbow pipework, fitted with flanges or pipe weld ends, with movement control rods attached to the joint hardware.This type of joint is used in applications where the pressure thrust loading on anchors and/or equipment is considered excessive, and where a change in the direction of the piping occurs.
Method of operation
The balancing bellows is subjected to the same line pressures as the flow bellows. As the flow bellows compresses, the tie rod devices make the balancing bellows extend an equal amount. Since there is no change in the volume of the system, the pressure forces remain in balance
Product code
Type PBFF – flanges both ends
Type PBWW – pipe weld ends both ends
Type PBFW – flange one end, weld end the other
Movement capability–Suitable for AxialSmall lateral movements
Bore size range– standard50 – 1500mm
Pressure rating– standard joints4, 10 and 20 bars – subject to pressure capability of attached hardware
Pipework system notes–Tie rod hardware is attached to contain pressure thrust forces and in many cases main anchors are not required. Minimum guiding
