What is an expansion joint?

According to the Expansion Joint Manufacturers Association (EJMA), an Expansion joint is a device that is made up of one or more metal bellows to absorb any dimensional changes caused by thermal expansion or contraction of a pipe-line, duct or vessel.

What is a metal bellow?

A metal bellow, consisting one or more corrugations is the flexible element of an Expansion Joint. It is typically composed of a light gauge metal tube of one or more ply formed in to a series of corrugations. Bellows Systems expansion joints can be manufactured from any material which has the necessary drawing quality, and the corrosion resistance required by the operating conditions of the system in which they might be installed. The pitch and depth of draw of any bellows can be varied and the shape modified to meet special requirements.

Multi-ply bellows are primarily used on expansion compensators as standard equipment and also on other large diameter expansion joints where significant reduction is compressive forces (spring stiffness) are desired. Toroidal bellows are used often where extremely high-pressure applications are encountered.

What are the different types of expansion joints?

There are several types of expansion joints. Each type of expansion joints is designed to operate under a specific set of design conditions. Some of the most common types of expansion joints are,

  • Single Expansion Joint
    • Single Tied Expansion Joints
  • Universal Expansion Joint
    • Dual Expansion Joint
    • Universal Tied Expansion Joint
  • Hinged Expansion Joint
    • Swing Expansion Joint
    • Gimbal Expansion Joint
  • Pressure-Balanced Expansion joint
    • Inline Pressure Balanced Expansion Joint
    • Elbow (type) Pressure Balanced Expansion Joint
  • Externally Pressurized Expansion Joint
  • Rectangular Expansion Joint
  • Composite Fabric Expansion Joint
  • Thick Wall Expansion Joint
    • Lens Type Thick Wall Expansion Joint
    • Flanged and Flued Thick Wall Expansion Joint
What are some of the expansion joint accessories?

An expansion joint by itself accommodates any axial, longitudinal and angular movements in a pipelines, ducts and vessels. The addition of accessories to an expansion joint increases the complexity but also, it’s capabilities. Some of the accessories for the expansion joints include,

  • Liners (Internal Sleeve)
    • Drop-In Liners
    • Bi-directional Liners (Dual Liners)
    • Integral Liners
  • Weld Ends
    • Pipe Weld End
    • Tubing Weld Ends
  • Flanges
  • Collars
  • External Cover
  • Root Rings
    • Hollow Reinforcing Rings
    • Solid Root Rings
  • Equalizing Rings
  • Control Rods
    • Limit Rods
    • Tie Rods
  • Pantographic Linkages
What are tie rods? Why do we need them?

Tie rods are devices, in the form of rods or bars that are attached to the expansion joint assembly whose primary function is to continuously restrain the full bellows pressure thrust during normal operation while permitting only lateral deflection. Often, the terms “limit rods” and “tie rods” are used interchangeably. In a strict sense, limit rods (stops) are used to restrict the range of movement of an expansion joint or its component parts.

Angular rotation can be accommodated only if 2 tie rods are used, located 90 deg opposed to the direction of rotation.

What are root rings?

Root rings fabricated from tubing or solid round bar stock, usually made from carbon steel or stainless-steel materials, serve to reinforce the bellows against internal pressure and also maintain the curvature of the root radius of the corrugation. The use of root rings is limited to special high-pressure applications with design pressures up to 2,000 psi.

What are the factors for choosing a bellow type?

While ordering bellows, here a few things are helpful for the customer to know,

  • Nominal size of the pipe (diameter) or ducting.
  • Pressure at which the system operates.
  • Temperature at which the system operates.
  • Possible direction of deflection and amount of deflection in the system.
  • Length of the pipe or duct system if known.
  • Flow medium and the velocity of flow.
  • Any applicable codes and standards.
    What are inputs needed for designing and manufacturing an expansion joint?

    Inputs needs to be decided based on customer requirement which may be replacement of existing bellow or new installation of an expansion joint.

    For Replacement of existing bellow, customer must specify

    • type of existing bellow that needs to replace
    • overall length of the exiting bellows
    • diameter of the existing bellow
    • Eng connection – flanged/clamped/welded
    • type of engine (If used inside an engine exhaust system)
    • Any existing design documentation

    For New installation of expansion joint customer must specify,

    • Nominal pipe / duct size
    • Pressure at which the system operates.
    • Temperature at which the system operates.
    • Spring rate desired (if available)
    • Cycle life desired (if available)
    • Length of the pipeline system (if the environment is a duct system).
    • Type of engine (if it is an engine system).
    • Desired end connection
    • Any applicable codes and specification