Expansion Joint (Bellow)
Expansion joints (Bellows), also known as bellows, are flexible devices that serve as pressure-containing elements in piping systems to absorb thermal expansion, contraction, and other mechanical movements. They are critical components in many industrial applications, particularly where thermal stresses or movement could compromise the integrity of the piping system.
The commonly used method to reduce thermal expansions is the creation of expansion loops by bending the pipes. However, these take up a lot of space. For example, as shown in the image below, when a 300mm diameter and 85m long pipe is heated from -10°C to +330°C, the pipe expands by approximately 380-400mm. The length of the expansion loop required to accommodate this should be between 5 and 7 meters. However, when sufficient space is unavailable, this solution is not feasible. In such cases, bellows-type expansion joints are used as a device when there is limited space.
Figure-1 shows the required expansion loop design. The lateral compensator at the end is the most suitable solution for facilities with limited space.
Figure-1
Expansion Loop and Bellow Comparison
Types of Expansion Joints
There are five types of bellows (expansion joints) in the piping industry.
1-Axial Expansion Joints:
Designed to absorb movements in the axial direction (along the pipe’s length).
It is commonly used to accommodate thermal expansion or contraction.
Figure-2
Axial Bellow: Designed to absorb movements in the axial direction (along the pipe’s length).
Axial Type Bellow Application
Rubber Type Axial Bellow Application
2-Lateral Expansion Joints:
Designed to absorb movements in the lateral direction (perpendicular to the pipe’s axis).
It is often used when the pipe needs to move sideways due to thermal changes or other external forces.
Figure-3
Designed to absorb movements in the lateral direction (perpendicular to the pipe’s axis).
Installation of lateral bellows in necessary places should be done pre-tensioned. This pre-tension amount should be half of the calculated thermal expansion. The above figure shows that the rods prevent the bellow from expanding in the axial direction.
Lateral Bellow Application
The figure shows that the rods prevent the bellow from expanding in the axial direction.
3-Angular Expansion Joints:
Allow angular rotation in the piping system.
Typically used in pairs to absorb angular movement, especially in elbows or turns.
Angular Bellow
Allow angular rotation in the piping system.
4-Universal Expansion Joints:
It is composed of two bellows connected by a central pipe or spool.
Capable of absorbing axial, lateral, and angular movements.
It is often used in systems where multiple movements coincide.
Universal Type Bellow
It is composed of two bellows connected by a central pipe or spool.
5-Pressure Balanced Expansion Joints:
Designed to absorb axial movement without transferring thrust to the pipe anchors.
Used in systems with high-pressure conditions where thrust forces need to be minimized.
Materials
Depending on the application, expansion joints are usually made from materials like stainless steel, rubber, or PTFE. Stainless steel is ordinary in high-temperature and high-pressure environments due to its strength and resistance to corrosion.
Applications
Thermal Expansion: Absorb the thermal expansion of pipes in high-temperature systems, such as steam or hot water lines.
Vibration Dampening: Isolate or dampen vibrations caused by pumps, compressors, or other mechanical equipment.
Misalignment Compensation: Adjust for slight misalignments in the piping system during installation or operation.
Absorbing Mechanical Movements: Compensate for mechanical movements in bridges, ships, or large industrial structures.
Design Considerations
Movement Capability: The expansion joint should handle the expected movements (axial, lateral, angular) in the system.
Pressure Rating: It must withstand the internal pressure of the system.
Temperature Range: The material and design must accommodate the operating temperature.
Cycle Life: The number of cycles the joint can withstand before failure is crucial in design, particularly in systems with frequent thermal cycling. Manufacturers often rate their commercial bellows to a safe operating limit of 3000 cycles, specified in their catalogs.
End Connections: Flanged, welded, or threaded connections depending on the piping system.
Standards and Codes
Several industry standards govern the design, manufacturing, and testing of expansion joints:
EJMA (Expansion Joint Manufacturers Association): Provides guidelines for designing and selecting metallic expansion joints.
ASME B31.3: Process Piping code covers design considerations for piping systems, including expansion joints.
EN 14917: European standard for metallic expansion joints.
