Metallic Expansion Joints

Restrained Metallic Expansion Joints

• Single Tied Pump Connectors
• Double Tied Lateral
• Single and Double Hinged
• Single and Double Gimbal
• In-Line and Elbow Pressure Balanced

Restrained metallic expansion joints are recognisable by the inclusion of some form of external steelwork or structure, typically taking the form of hinges, gimbal (or cardan) rings or tie-rod assemblies.

These structures form an integral part of the expansion joint design, both in terms of movement capacity and pressure containment, and ensure that when pressurised during operation, only minimal loads and forces are transferred to adjacent pipework, nozzle connections and equipment, thus allowing the use of relatively light system anchors.

Unrestrained Metallic Expansion Joints

• Single Axial
• Double Axial (often referred to as a 'Universal' Expansion Joint)

A single axial expansion joint is characterised by a single bank of convolutions and typically with flanged or schedule pipe end connections, although we can accommodate pretty well any termination requirement. Although single axial expansion joints can accommodate a relatively small amount of lateral and angulation movements, they are predominantly utilised in systems where only axial compression and/or extension are required.

A double axial expansion joint is recognisable by two banks of convolutions connected by a central pipe section or spool. Although these joints can accommodate both axial and angulation movements, they are predominantly installed where appreciable amounts of lateral, or sideways travel, are required.

Although unrestrained joints can be found in higher pressure applications, such as heat exchangers and process pipework, they are more commonly found in lower pressure environments, such as exhaust manifolds, flue gas systems, or in building services carrying LTHW, steam and condensate in relatively small diameter pipework.

Particularly relevant to long straight runs of pipework, when pressurised, unrestrained metallic expansion joints transfer forces onto adjacent pipework, plant items and equipment through what is known as ‘pressure thrust force’, which is a function of internal pressure multiplied by the effective area of the expansion joint convolutions, or membrane as it is commonly referred to.

In such cases, care should be taken to ensure that suitable termination anchors are installed to overcome the effects of pressure thrust force on the wider system.