Why are Metal Expansion Joints Important?

Where piping designs are subject to changes in temperature, pressure, vibration, compression extension, cyclical movements or movements required in usage, flexible metal hose and metal expansion joints, in tandem or alone, are needed to preserve the integrity of your system.


Factors Determining the Selection of Bellows

The physical properties of any material varies with temperature. Limits for operating temperature are affected by the working pressure, the type of media being conveyed and the nature of the application. By careful selection of material, it is possible to provide an expansion joint for a wide range of operating temperatures. The choice of type, metal alloy, end fitting and method of fitting attachment determines the temperature limit.

The nominal pressure ratings of an expansion joint varies according to type, material and size. Specific pressure ratings for each type of an expansion joint are calculated according to the applicable design specification. Under actual working conditions, pressure is affected by many other factors such as temperature, pulsating conditions, bending stresses, shock, vibration, and external influences

The type of media being conveyed is an important consideration in the selection process. An expansion joint is subject to corrosion by both the material flowing through it and the outside environment. For almost all applications, an expansion joint can be selected that is resistant to the intended media.

The size of an expansion joint is specified by the nominal diameter. The existing piping will normally dictate the size of the metal hose for a particular application. However, flow rate, velocity, and pressure drop considerations may also influence the selection of the expansion joint.

The use of an expansion joint is complemented by the extensive range of end fittings that are available. Such end fittings may be male or female pipe threads, unions, flanges, flared tube fittings, or other specially designed connectors. End fittings are attached by welding, silver brazing, soldering depending on the type of the expansion joint and the alloy.

Untied Expansion Joints

Tied Expansion Joints

  • Axial Expansion Joints — Singular or dual bellows with installation fittings only
  • Double Expansion Joint — Commonly used for low-pressure service
  • Internally Guided Expansion Joint — Simple design = less expensive
  • Untied Universal Expansion Joints — All degrees of freedom (axial, lateral, angular)
  • Pressure Balanced Expansion Joint — Anchors affected by bellows spring rate and pressure thrust = higher force
  • Hinged Expansion Joints — Single or dual bellows with restraining hardware
  • In-line Pressure Balance Expansion Joint — Typically used for high-pressure service
  • Gimballed Expansion Joints — Limited degrees of freedom
  • Tied Single & Universal Expansion Joints — Anchors only affected by bellows spring rate = low force