In process piping systems, where variables include temperature and pressure fluctuations, the effects of vibrations and movements can apply stresses to the system components if movement isn't controlled properly. Knowing the types of metal expansion joints available will make choosing a system type for particular movement and working conditions easier. Metallic expansion joints are composed of bellows for controlled movement that maintain pressure integrity.
But that design depends on which condition needs to be managed, as one joint may take mostly axial movement while designs called "hinged," "gimbal," "universal," or "pressure-balanced" are used for other possibilities.
Here is a guide to the most common metallic expansion joint types and their capacity, uses, considerations for selection, and some of the many benefits.
A metal expansion joint is a type of flexible piping component installed in the straight runs of pipe, ductwork, or connected equipment. The purpose is to accommodate some of the motion that the piping system otherwise could not absorb. The flexible component is typically a metallic bellows or hose, a very thin-walled part with very closely spaced convolutes (corrugations).
The convolutions give the bellows the ability to expand or contract as needed without rupture and still maintain its ability to contain internally developed pressure.
Depending on construction, the joint will absorb either axial extension or compression and lateral or angled motion. One of the major reasons for the implementation of an expansion joint is thermal expansion of the pipe. It is also used to control stresses developed as a result of system motion and to offset settling of piping.
For a broader explanation of their purpose, construction, and working principle, What are expansion joints provides useful background before moving into specific metallic designs.
The bellows are the working components of a metal expansion joint. The wall thickness, convolution shape and geometry, material of construction, number of convolutions, and their dimensions dictate a bellows' flexibility, pressure-sustaining capabilities, and fatigue life.
The bellows must be engineered considering the actual movement to be undergone and service environment conditions; excessive movement, high pressures, or incorrect installation will decrease the life of the bellows.
There are several different types of expansion joints, with each configuration designed around a particular movement pattern or piping requirement. Flexibel's metallic expansion joints series provides a wide range of solutions: single, universal, hinged, gimbal, jacketed, reinforced, externally pressurized, two-ply tested, pressure-balanced, rectangular, and pantographic linkage expansion joints.
Metallic single expansion joint consists of a single bellows and is typically used to absorb the axial thermal expansion/contraction of piping. The bellows will compress/expand as the piping expands/contracts along its longitudinal direction.
It may also be used to absorb small amounts of lateral/angular displacement in some constructions. This type of installation could typically be chosen for uncomplicated pipelines where the axial expansion is the main concern.
In a metallic universal expansion joint, two bellows are joined through the use of a central spool. With this setup, you increase the capability for lateral movement; along with that, you allow for axial and angular movement.
This is practical in configurations in which movements occur in more than one dimension. The length of the center spool will have an impact on lateral movement capability.
A metallic hinged expansion joint uses a bellows combined with hinge mechanisms that control angular movement in one plane. The hinges also restrain pressure thrust and prevent uncontrolled movement.
This makes the design useful in systems where thermal growth needs to follow a defined movement path rather than allowing the bellows to move freely in every direction.
A metallic gimbal expansion joint incorporates a floating gimbal ring held between two pairs of hinged mechanisms, with the aim of accepting angular deflection in all directions whilst isolating the thrust.
A practical application of these in piping is in locations where movement is allowed at some angles.
A metallic reinforced expansion joint is constructed by embedding steel rings in the bellows to enhance structural support. A reinforced expansion joint can be chosen for applications when the expansion joint is exposed to critical internal pressure demands.
Reinforcement design is another element in the total design and should be designed with considerations for pressure, temperature, movement, and cycle requirements.
In a metallic jacketed expansion joint, a casing is placed around the bellows assembly. This outer jacket can facilitate controlled heating or cooling to the line.
This setup is often used when the temperature control of the process stream is crucial, especially when handling viscous or temperature-sensitive materials.
An metallic externally pressurized expansion joint design has the effect that the internal pressure in the system is actually pushing on the outside of the bellows. The net result of this design is to keep the bellows stable while allowing for long axial motion.
The design is well suited for long pipeline runs that need to compensate for long axial thermal expansion. Flexibel uses this design specifically for long-stroke axial movement and also with district heating, cryogenics, and steam distribution.
The metallic two ply testable expansion joint design incorporates two bellows members and allows for detection of bellows integrity, making it relevant for a large number of critical services where detecting a leak at an early stage is crucial.
The secondary bellows member & the test arrangement can give you an extra element of monitoring compared to the conventional one-ply unit.
Metallic pressure balanced expansion joints are designed to absorb movement while balancing the pressure thrust generated by the bellows. Reducing the transferred pressure-related loads at anchors or adjacent equipment is possible with this kind of design.
Available as elbow-type and linear configurations. Good for equipment where the overpressure thrust would cause unexpected load on the piping system at locations around the equipment with unusual piping geometry.
Not all industrial flow paths take a circular form, however. metallic rectangular expansion joints are designed to accommodate square, rectangular, and other similar non circular ducting.
The design will absorb axial, lateral, and angular motion in large ducted systems and is typically investigated for flue-gas, exhaust/ventilation, and power-generation use.
A metallic pantographic linkage expansion joint uses a pantographic linkage arrangement to mechanically convey motion from one or multiple bellows. These mechanical linkages help control movement and can be beneficial in systems involving large, networked movements.
This is actually a peculiar one, since the necessary motion is beyond the capacity of an ordinary single bellows arrangement.
Metal expansion joints are used across industries where piping or ductwork experiences thermal growth, vibration, pressure changes, or structural movement. They help accommodate these movements while maintaining the integrity of the system and reducing stress on connected components. Proper selection and installation are important to ensure reliable performance under operating conditions.
The movement requirement is one of the most important factors when comparing types of bellows expansion joints. A joint should be chosen so that it will be put to the movement it's designed for, in respect of direction and scale.
Axial movement occurs along the longitudinal axis of the pipe. An axial metal expansion joint is primarily used when the piping expands or contracts along its length because of temperature changes. This can also be seen frequently with straight pipe runs and with predictable movement caused by thermal growth, which can be guided between expansion anchors and guides designed correctly.
Lateral movement is the direction of movement perpendicular to the pipe axis. Universal expansion joints are generally used when larger lateral deflections need to be accommodated. Lateral deflection will vary depending on the geometry, the bellows design, spool length, and the conditions in which the joint operates.
One of the planes of movement would be angular, where movement at either end of a joint will take place at a different angle relative to the other. Hinged joints manage angular movement within a single plane, whereas other configurations such as a gimbal system can move within several planes. This is required where pipe expansion has to take a direction.
Certain systems may be undergoing axial, lateral, and angular movement simultaneously. In this event, the entire pipeline layout should be reviewed rather than choosing a fitting according to one single movement value.
Movement calculation must take into account operating temperature, installation condition, anchors and guides, equipment, and number of cycles.
Understanding how different expansion joints accommodate movement is essential when selecting the right solution for a piping system, and the key differences are explained in our guide to Axial vs Angular vs Lateral Expansion Joints.
Metal expansion joint size, pressure rating, and temperature capability are dependent on design, material, bellows construction, and application. In Flexibel's metallic range, sizes go up to large-diameter applications from industrial sizes, with some products listed up to DN5000.
| Parameter | Flexibel Metallic Expansion Joints |
|---|---|
| Nominal Size | DN50 to DN5000, depending on configuration |
| Pressure Rating | Up to 100 bar for selected designs |
| Temperature Range | Approximately -196°C to +800°C, depending on material and configuration |
| Bellows Materials | SS304, SS316L, SS321, Inconel, Hastelloy and other suitable alloys |
| Movement Types | Axial, lateral, angular and combined movement, depending on joint design |
| Available Configurations | Single, Universal, Hinged, Gimbal, Reinforced, Jacketed, Externally Pressurized, Two-Ply Testable, Pressure Balanced, Rectangular and Pantographic |
| Application Suitability | Oil & gas, petrochemical, power generation, marine, steel, valve and industrial piping systems |
When selecting the right metallic expansion joint, one should start with the physical situation, not just what can be selected from the stock size in a given catalogue. The conditions under which it will function must be known throughout the life of the element.
1. Identify the Required Movement: When selecting the right expansion joint, one should start with the physical situation, not just what can be selected from the stock size in a given catalogue. The conditions under which it will function must be known throughout the life of the element.
2. Check Operating Pressure and Temperature: Consider the standard operating temperatures, plus the maximum and minimum temperature, variation of pressure, and also potential transient conditions. They will be related directly to the design of the bellows and hence their material choice.
3. Consider the Piping Layout: The appropriateness of any given joint arrangement can be influenced by anchors, guides, elbows, equipment hook-up, and space limitations. No joint is meant to overcome inadequate support or line-up, and it should be considered as a component of a well-designed piping system.
4. Check Media Compatibility: The process medium should be compatible with the bellows material as well as with the other wetted parts. The most common application uses stainless steel. High-demand services would normally require alloyed metals like Inconel and Hastelloy. The above list in Flexibel indicates SS304, SS316L, SS321, Inconel, Hastelloy, and other materials based on need.
Before finalizing a metal expansion joint, it is also important to verify its condition and installation requirements. An expansion joint inspection checklist can help engineers and maintenance teams review key points such as bellows condition, connections, alignment, supports, and signs of wear or damage.
When properly selected and engineered, metallic expansion joints can provide several benefits to industrial piping systems. They can help reduce stress on connected equipment, accommodate movement, and improve the overall reliability of the piping system. Their performance also depends on choosing the right joint type, material, and design for the operating conditions.
Made in the UAE, Flexibel is a metallic expansion joint manufacturer offering various configurations of metallic expansion joints for piping applications across industries. Its own metallic product line incorporates single, universal, hinged, gimbal, reinforced, jacketed, externally pressurized, double-ply tested, pressure-balanced, rectangular, and pantographic linkage solutions.
Its own design philosophy considers factors such as pressure, temperature, cycle life, amount of movement required, material required, etc in the provision of a solution for the specification of expansion joints.
It also indicates that it has EJMA, ASME B31.3, and applicable ISO/DIN/EN specifications regarding its designs.
Some of its quality checks (may vary depending on job specification) are material identification, dimensional control, weld inspection, NDT, pressure testing, and leak testing. This allows a solution based on actual operating conditions, instead of thinking that all metallic expansion joints are the same.
Understanding the types of metal expansion joints is important when designing or maintaining industrial piping systems because each configuration responds differently to movement and pressure conditions. Always start with the system, not the product, as temperature, pressure, direction of travel, number of cycles (cycle frequency), material in process, geometry of the piping system, anchorability, and spatial limitations of the application dictate your decision process.
Proper engineering is crucial to service life, as bellows work through cycling with correct design, material, and installation conditions; a metallic expansion joint can actually contribute positively to your piping stresses, linked equipment reliability, and overall system reliability.
