Metal expansion joints are flexible connections to allow axial, lateral or angular motion. They are installed in industrial piping, pressure vessels, heat exchangers and other pressurised systems to accommodate expansion and vibration caused by changes in temperature, pressure and/or fluids.
An expansion joint is generally used in four types of applications: primarily thermal expansion and contraction, and in addition
- to correct problems of misalignment
- to provide flexibility in manual handling operations
- to compensate for regular or constant movement
- to absorb vibration.
Specific pressure loadings (max. allowable design pressure) for each type of an expansion joint should be calculated according to the applicable design code. Under actual working conditions, pressure is affected by many other factors such as temperature, pulsating conditions, bending stresses, shock, fluids, corrosion influence, vibration, and external influences.
Expansion joint are designed and manufactured the bellows in terms of maximum displacement per corrugation and maximum working pressure. These maximum pressure and deflection limits are critical in determining the bellows cycle life. Overpressurisation in service or during a hydro-test will cause damage to the bellows that could result in a reduced cycle life or failure.
Metal bellows are made of one or multiple plies of stainless steel, heat resistant low-alloy steels, austenitic steel, nickel and nickel-alloy steels or other formable materials.
Classification of Metal Expansion Joints in acc. to PED
Expansion Joints are pressure accessories in acc. to PED. Therefore they must be classified with the nominal diameter and the max. allowable pressure PS according to the diagrams 6 to 9 of Annex II. For category I to IV, the CE marking is required if they are placed on the market separately.
see also PED CATEGORY CALCULATOR for Piping and Pressure Accessories
Bellows design types
A bellow is a flexible element consisting of one or more convolutions and the end tangents. The typical shape is the
- unreinforced U-shaped bellows
- reinforced U-shaped bellows
- toroidal bellows
subject to internal or external pressure and cyclic displacement. The individual bellows are produced by a rolling forming machine.
Different Bellows designs with regard to the number of layers
- Single ply bellows
Most bellows are manufactured from a single ply of sheet material of sufficient thickness to limit the circumferential stress to be below the maximum allowable limit. Single ply bellows are suitable for all applications that have relatively small movements. Single ply applications are preferably suitable for low pressure and vacuum applications. - Multi-ply bellows
However, when increase cycle life or a less-stiff bellows is required, a bellows may be manufactured having two or more thinner plies, that when taken together, provide the same pressure capacity but distribute the bending stresses among the plies. The maximum bending stress in each ply is greatly reduced, resulting in a much better fatigue resistance. - Redundant-ply bellows
Redundant-ply bellows differ from multi-ply bellows in that each ply of a redundant-ply bellows is sufficient to act alone in providing sufficient thickness for pressure design. No advantage is typically gained in fatigue resistance, and the bellows is stiffer than a single-ply bellow.
Metal expansion joints types
- Single Expansion Joint
This is the simplest form of expansion joint. A single-bellows construction, which absorbs movement of the pipe section into which installed. - Double Expansion Joint
A double expansion joint consists of two bellows jointed by a common connector that is anchored to some rigid part of the installation by means of an anchor base. The anchor base may be attached to the common connector either at installation or time of manufacture. Each bellows of a double expansion joint functions independently as a single unit.
Double bellows expansion joins should not be confused with used with universal expansion joint. - Universal Expansion Joint
Universal expansion joint containing two bellows joined by a common connector for the purpose of absorbing any combination of three basic movements (that is, axial motion, lateral deflection, and angular rotation). A universal expansion joint is used, in cases, to accommodate greater amounts of lateral movement than can be absorbed by a single expansion joint. - Tied Universal Expansion Joint
Tied universal expansion joint, used when it is necessary for the assembly to eliminate pressure thrust forces from the piping system. In this design, the expansion joint will absorb lateral movement and will not absorb any axial movement external to the tied length. - Swing Extension Joint
Swing expansion joint designed to absorb lateral deflection and/or angular rotation in one plane only by the use of swing bars, each of which is pinned at or near the ends of the unit. - Hinged Expansion Joint
Hinged expansion joint containing one bellows and designed to permit angular rotation in one plane only by the use of a pair of pins running through plates attached to the expansion joint ends. Hinged expansion joints are typically used in sets of two or three to function properly. - Gimbal Expansion Joint
Gimbal type expansion joints are designed to permit angular rotation in any plane by the use of two pairs of hinges affixed to a common floating. Simply, a double gimbal expansion joint is consisted of two single gimbal expansionjoints and an intermediate pipe connects them each other. The advantage of this arrangement is the ability to absorb a large lateral movement in any plane at each end. Because the gimbals are attached to each end of the bellows, the thermal expansion of the intermediate pipe will not be absorbed by the universal but must be accepted by the adjacent piping. - Pressure-Balanced Expansion Joint
Pressure-balanced expansion joint designed to absorb axial movement and/or lateral deflection while retaining the bellows pressure thrust force by means of the devices interconnecting the flow bellows with an opposed bellows also subjected to line pressure. This type of joint is typically installed where a change of direction occurs in a run of pipe, although “in-line” pressure-balanced expansion joints are also available.
Metal Expansion joints in Piping Systems
Bellows expansion joints are usually the generally type for pipings. Other expansion joint types are possible, if the piping code this allowed, such as
- Slip Type expansion joints in acc. to piping code B31.3 para. 304.7.4 or other type of bellows shall be qualified as required by para. 304.7.2
Table: Overview of Codes, Standards and other Specification for Expansion Joints
| EN 13480 series | EN 14917 | Germany AD 2000 B13 | ASME B31.1 App. P | ASME B31.3 App. X | EJMA Rules | |
|---|---|---|---|---|---|---|
| Application | Industrial Piping | Pressure Vessel and Piping | Pressure Vessel and Piping | Power Piping | Process Piping | General applications |
| General Notes | CE Marking and EU-Declaration of Conformity by assembly manufacturer | EU harmonised product standard; CE Marking and EU-Declaration of Conformity | Specification for single-ply design Bellows Expansion Joints | This Piping Code contains additional requirements to EJMA Rules; | This Piping Code contains additional requirements to EJMA Rules; see also App. F / F304.7 | This rules are referred in any Piping Codes |
| Scope & Limits | PS > 0,5 bar; Bellows Expansion Joints: a) Intended to installed industrial piping (assembly manufacturer) b) Manufacturer of expansion joint is not piping manufacturer | Bellows Expansion Joints for pressurised applications; | Single ply Bellows Expansion Joints for Pressure vessel and industrial piping | MAWP > 15 psi = 1 bar; Bellows Expansion Joints; | MAWP > 15 psi = 1 bar; Bellows Expansion Joints; | Metallic Bellows Expansion Joints for generally applications |
| PED harmonised standard | Yes | Yes | No | No | No | No |
| Pressure thrust loading incl. combined other movements | Yes | Yes | Yes | Yes | App. X / F304.7 | Yes |
| Angular rotation (rotating movement) | EN 13480-3/ Clause 6.5 Annex C | Yes | Yes | Yes | Yes | Yes |
| Axial movement | required anchor and additional guides | required anchor and additional guides | Yes | Yes | Yes | Yes |
| Lateral deflection | Yes | Yes | Yes | Yes | Yes | Yes |
| Universal | required anchor and additional guides | required anchor and additional guides | No | Yes | Yes | Yes |
| Single-ply | Yes | Yes | Yes | Yes | Yes | Yes |
| Multiple-ply | Yes | Yes | No | Yes | Yes | Yes, max 5 |
| Calculation of the allowable number of cycles | Yes | Yes | Yes | Yes | Yes | Yes |
| Stresses and Instability due to internal pressure | Yes | Yes | Yes | Yes | Yes | Yes |
| Fatigue evaluation | Yes | Yes | App. P / P-3.2 | App. X / X302 | Yes | |
| External pressure design | No | Yes | Yes | Yes | Yes | Yes |
| Design general | Calculation acc. EN 14917 | Yes | Yes | App. P / P-3.1 | App. X / X301 | Yes |
| Unreinforced U-shaped bellows | Yes | Section 6.2.3 | Yes | Yes | Yes | Yes |
| U-shaped reinforced bellows | Yes | Section 6.2.4 | No | Yes | Yes | Yes |
| Toroidal bellows | Yes | Section 6.2.5 | No | Yes | Yes | Yes |
| Fabrication | EN 13480-4 | Section 7 | No | App. P / P-3.2 | App. X/ X302.2 | Yes |
| Inspection and testing | EN 13480-5 | Section 8 | No | App. P / P-3.2 | App. X/ X302.2 | Yes |
| Marking | Assembly marking by name plate incl. CE Marking; Separate marking by name plate if other manufacturer as the piping manufacturer; | Separate marking by name plate | Code requirements | Piping Code requirements | Piping Code requirements | No |
| Operating/installation instruction | Required, incl. information to piping system analysis | Section 8.7.3 | No | Piping Code requirements | Piping Code requirements | Yes |
| Installation and shipment | Yes | Section 10.3 Annex C | No | Yes | Yes | Yes |
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Metal Expansion Joints for Pressure Vessels: Applicable Codes and Standards
