The way a piping system moves determines which expansion joint configuration it needs. An axial expansion joint, angular expansion joint, and lateral expansion joint each accommodate movement in a different direction, even though their overall purpose is similar.
A metallic expansion joint can be selected based on the type and amount of movement the piping system needs to accommodate. Industrial piping can also be exposed to strain from temperature variation, vibration, displacement of a structure, and the movement of equipment. Knowledge of these various movements will allow designers to choose a joint that is compatible with the arrangement, rather than imposing extraneous strains on bellows, equipment, supports, etc. This document compares axial, angular, and lateral expansion joints. It also describes what these joints are, their applications, and considerations in design selection.
An industrial pipe can experience movement during its entire lifespan. Thermal expansion/contraction can take place due to temperature variations, and vibration can arise from pumps, compressors, turbines, or other machinery; even structural settlement and changes in operating conditions can affect the piping configuration. Expansion joints for thermal expansion are commonly used to accommodate calculated movement caused by temperature changes while helping control stress within the piping system.
An expansion joint is designed in the same way to limit the excessive stresses on the piping system and allow a controlled flexible movement (which will then accommodate calculated movement). A metallic expansion joint utilizes corrugations (like a concertina), which are flexible and will not lose the contents from inside.
The principle can seem simplistic but is actually quite complex. An expansion joint has to be designed to take the correct amount of the desired movement. For a broader explanation of their purpose and working principle, What are expansion joints provides a useful introduction before comparing the individual configurations.
Movement is not only how much pipe will move but also in what direction it will move. A pipe can stretch (axial), sway laterally, or twist around a given center point (rotary). All of these are significantly different operating environments and need a unique type of expansion joint. Using the wrong type of joint for the expected movement could result in overstressing of bellows or introduce loads elsewhere in the system.
An axial expansion joint is intended to accommodate motion along the axis of the pipeline. Typically used in moderately straight runs of pipe due to thermal growth and contraction.
When a pipe expands due to temperature increases, it grows longer. When the pipe cools, it shrinks. An axial joint allows this predetermined growth through extension or compression of the bellows.
Axial motion is relative to the centerline of the expansion joint, and it is when there is relative motion between the attached piping segments moving towards or away from each other, compressing or elongating the bellows.
The extent of absorption depends on such characteristics as bellows geometry and material, number of convolutions, working pressure, temperature, and conditions.
An axial movement expansion joint is therefore generally considered when longitudinal movement is the dominant requirement. However, the piping system must also have suitable anchors and guides to control where that movement takes place.
The use of axial expansion joints usually occurs when the majority of movement is along the direction of the piping system itself. These joints can be best used to compensate for thermal expansion or contraction. One may even use an axial joint with:
With conventional axial joints, we have the issue of pressure thrust. It should be borne in mind that when designing a pipe support system, we need to allow for the forces resulting from internal pressure.
An angular expansion joint accommodates motion by permitting one part of the pipe to rotate about another part. So, the bellows are not just able to compress and expand; they may also bow over as the angular motion takes place.
Hinged and gimbal-type expansion joints are frequent designs intended for angular motion, and mechanical fixtures will direct the motion and may or may not restrain the pressure thrust.
In essence, angular movement is rotation by an angle. When the adjoining pipes are moved apart to change the angle between them, the connector mechanism permits the rotation to be within its defined range of angular movement.
An angular movement expansion joint is particularly useful where the piping arrangement contains offsets, bends, or equipment connections that require movement to occur through rotation.
When using the hinged configuration, a controlled plane of rotation can be maintained. With the gimbal configuration, you are capable of performing controlled planes of rotation in many planes.
Angular expansion joints are appropriate where pipe movement is based on rotation, and not simple axial movement. They provide a method for directing thermal and mechanical movement through a defined plane and are also used for taking the pressure thrust of piping systems. Types of angular configurations:
You must take into account the hardware and direction of movement of the joint when included as part of the whole piping design.
A lateral expansion joint accepts movement perpendicular to the longitudinal axis of the pipe. Thus, the two connections accept sideways movement relative to each other in this case.
Universal joints often go with lateral movement; for obvious reasons, they offer more flex than a standard single bellow joint in a standard arrangement with two bellows.
Lateral movement: Any condition in which one part of piping moves laterally relative to another part. The expansion bellows will compress to tolerate this movement and stay within the deflection limit.
A lateral movement expansion joint may be appropriate where piping geometry creates an offset or where thermal movement needs to be distributed across a flexible section.
Actual lateral displacement capability relies on the shape of the bellows, distance between the bellows, pressure, temperature, and various design parameters.
Lateral expansion joints are used when the piping system needs to accommodate movement perpendicular to its main axis. They are especially useful in layouts where thermal growth or structural movement creates sideways displacement between connected pipe sections. Lateral configurations may be considered for:
The pipework should be analyzed carefully, as lateral displacement tends to occur in tandem with the location of the anchor point, guides, and various supports.
The primary difference between the two configurations centers on the plane in which the joint is meant to allow movement to occur. Understanding the expansion joint movement types makes the selection process much clearer.
| Feature | Axial Expansion Joint | Angular Expansion Joint | Lateral Expansion Joint |
|---|---|---|---|
| Primary movement | Along pipe axis | Rotational movement | Perpendicular to pipe axis |
| Typical configuration | Single bellows | Hinged or gimbal | Universal |
| Movement form | Compression or extension | Angular rotation | Sideways displacement |
| Common cause | Thermal expansion/contraction | Piping rotation or thermal movement | Thermal growth across offsets |
| Pressure thrust | Usually managed through anchors | Restrained by hinges | Depends on configuration |
| Key support requirement | Anchors and guides | Controlled movement arrangement | Anchors and guides |
| Typical application | Straight piping runs | Directional piping layouts | Complex or offset piping |
Not solely based on the direction of movement can the correct choice be made. The decision must also consider: Pressure, temperature, cycle frequency, medium, available space, piping geometry, and associated machinery.
For systems requiring a specific metallic configuration, Flexibel's range includes single, universal, hinged, gimbal, reinforced, jacketed, externally pressurized, two-ply testable, pressure-balanced, rectangular, and pantographic linkage designs.
There are types of configurations that can handle more than one type of movement; however, this doesn't mean that one size fits all. The universal expansion joint, for instance, allows lateral motion and, in some applications, can also absorb axial motion at values not exceeding limits designed into its own configuration.
Hinged and gimbal configurations are built to handle angular motion in one case while managing how the bellows flexes in another. The difference is in defining something that CAN be deformed and something designed to handle the particular kind of motion it should have.
Multiple types of movement can occur in industrial piping at once. A hot process line can have thermal expansion at the same time as the connected equipment adds vibration or movement to structures. The design assessment should therefore consider:
This is more true in critical systems, where a considerable amount of cycling can shorten the lifetime of a bellows.
You need to select the piping system before selecting from the product catalogue. Selecting the right metallic expansion joint requires considering the type of movement, operating conditions, and support methods used. The joint should correspond to the requirements of the piping system. Appropriate matching will help avoid transferring excessive force to other points.
1. Determine the Required Movement: Determine whether a given axis demands axial or angular, linear, and/or translational movement. Actual or predicted motion will be calculated from operating and installation variables, rather than from a drawing estimation.
2. Calculate Thermal Movement: Temperature variations may result in considerable pipe expansion and contraction. The resultant movement is a function of the pipe length, pipe material, pipe coefficient of thermal expansion, and temperature differential. Where expansion/contraction due to temperature change is the primary issue, designers must use the full range of operating temperatures and expected cycles.
3. Review Pressure and Temperature: Don't forget the actual operating pressure and temperature together with the maximum and minimum operating conditions. Varying pressures, thermal cycles, and transient conditions affect the requirements for the joint.
4. Check Anchors and Guides: Anchors will absorb the motion, and guides will steer the pipe in the desired direction. Their positioning depends largely on the manner in which the expansion joint assembly is arranged. An expansion joint should never be used to compensate for improper supports or piping.
5. Consider the Process Medium: The material for the bellows and all other wetted components must be compatible with the process fluid. Metallic bellows commonly employ stainless steels, while more arduous services may incorporate alloy steels.
6. Review the Installation Arrangement: Care should be taken to install the fitting, ensuring space is available for the joint and that it will articulate within its full range of movement. Consider alignment of both components, support of fitting, support/restraints for shipment, etc.
The appropriate configuration varies according to the industry's operating conditions and piping layout. The movement requirements and joint design should therefore be evaluated in relation to the complete piping system, rather than treating each application as having the same movement conditions.
Long process lines in refineries and petrochemical facilities are exposed to high temperatures, variations in pressure and vibration, and corrosive process media. Metallic expansion joints in the oil and gas industry are used to accommodate calculated thermal and mechanical movements in these demanding piping systems. Whether an axial, universal hinged, gimbal, or pressure-balanced piping arrangement is used will depend on the type of movement predicted.
Large amounts of thermal expansion can occur in the steam, boiler, turbine, and exhaust piping from startup, operation, and shutdown. Flexible joints offer guided flexibility and minimize loading transmitted to equipment.
Both hot water systems and cold water systems, steam, and etc utilities will go through a number of cycles of heating and cooling. Linear pipes can accommodate axial systems, or more complex pipework can accommodate universal and angular systems.
Marine piping may be subject to vibration, thermal expansion and contraction, and displacement of equipment; structural deflections can occur. Limited space could also dictate the arrangement and dimensions of joints.
For chemical manufacturing, water treatment, and general industrial applications, the pipework can often be complex with multi-directional movements. The selection has to take the entire system into account, not just the nominal diameter of the pipe.
The service life and behavior of a fitting under movement conditions may be deteriorated by selection mistakes, even under seemingly simple movement conditions. A point of service life management is evaluation of a fitting with respect to real piping conditions and required movement, not a universal standard.
If an existing joint has reached the end of its useful service life, replacement of expansion joints should be approached as an engineering decision based on condition, operating history, and the requirements of the piping system. Before replacing the joint, an expansion joint installation guide can also help engineers review the correct installation procedure, alignment, supports, and other key requirements.
Flexibel is a expansion joints manufacturer in the UAE that offers a complete configuration range to meet industrial piping needs. This range includes single, universal, hinged, gimbal, reinforced, jacketed, externally pressurized, two-ply testable, pressure-balanced, rectangular, and pantographic linkage expansion joints. The engineering and design service supports EJMA and relevant international codes; the quality system provides material checks, dimensional checks, weld checks, non-destructive tests, and pressure and leak checks as per product and project specifications. Pressure, temperature, movement, material, cycle life, and piping geometry considerations are the factors that drive engineering for application. Flexibel supports oil and gas, power generation, marine, steel, valve, and other process industries in the UAE region, manufacturing and providing engineered expansion joints.
Axial, angular and lateral expansion joints all play different, distinct part in industrial piping. The ability to distinguish is important when you consider controlling movement to an expected performance. But selecting a joint is more than deciding direction. Pressure, temperature, total movement, cycles, service fluid, piping layout, location of anchors and guides, and load of connecting equipment are taken into consideration for final application.
Certain special joint designs may handle more than one direction of movement; but they must be carefully engineered to conditions imposed upon them at their point of application. Right selection and application keep stress away from the bellows and help alleviate load on equipment. You will find assistance from experienced expansion joint manufacturers in the final assembly for most strenuous industrial requirements.
