Description

Expansion joints connect two fixed assemblies or pipes and allow movement due to service load, shock, or thermal cycles.

Construction

They are made of elastomer, fabric or metal materials and feature a bellows-style construction. Convolutions permit misalignment, movement or isolation of the components that are joined together.

• Elastomer/fabric expansion joints are made of elastomeric material or fabric. They provide flexibility.
• Pipe expansion expansion joints are used in plumbing or piping applications.
• Vacuum or process-gas systems have vacuum flanges and fittings connect which run pipes or tubes to other sections of pipes or tubes, as well as to hoses, valves, pumps, chambers and vacuum components.
• Electrical conduits are also available for expansion joints.
• Metal bellows are expansion joints made of metal.

Size and Shape

Shape, application, and units of measure are related considerations.

Shape

Expansion joints can have a round, square, or rectangular cross-section.

• Rounded products often have a neck or collar that permits attachment with a hose clamp.

• Expansion joints with a flanged end usually attach to components with screws or bolts.

Size

Size is an important parameter when specifying expansion joints. For round expansion joints, enter the size as the diameter. For square or rectangular expansion joints, enter the size as the width. Do not, however, use the diameter or width for plumbing or piping applications. Instead, use the standard pipe-size options.

Scale

In terms of scale, expansion joints can use English or metric units of measure.

• English products are measured in inches (in.) or fractions of inches. English sizes that are less than or greater than 36 in. are also available.
• Metric products are measured in millimeters (mm).   Metric pipe sizes are specified by range. Metric pipe sizes that are less than 10 mm or greater than 1000 mm are also available.

Standards

Expansion joints must adhere to certain standards to ensure proper design and functionality.

ASTM F1007 - This specification covers the design, manufacturing, and testing of packed slip-type expansion joints used in pipelines for accommodating axial thermal growth or contraction from the pipeline carrying fluid.

BS 6129-1 - Guidance on selection, application and location of the various forms of joints with particular reference to choice of materials, shop tests, packing, protection, installation, system tests and maintenance.

References

Image Credit:

American BOA, INC. | Nor-Cal Products, INC.