An expansion joint bridges gaps through building assemblies and accommodates expected movements. Its position within a structure, movement types, environment and flow medium conditions are key factors in selection and design. Expansion Joints come in a variety of shapes, sizes, and materials. Important add-ons like flow liners, insulation, and stainless steel caps help to protect the expansion joint from abrasive, corrosive or toxic materials in the flow medium.
For a metal expansion joint, its strength and performance is determined by the material chosen, the fabrication process used, and the temperature and pressure at which it operates. An expansion joint’s ability to withstand a range of axial, lateral and angular movements is also determined by the bellows material. Metal bellows can be constructed from a number of alloys, including stainless steel. A typical metal bellows is produced using a cold-work method that plastically deforms the alloy below its recrystallization temperature. This procedure increases the bellows’ strength while maintaining its precise geometry. Some dishonest expansion joint manufacturers omit this cold-working process, which lowers the bellows’ final performance capabilities.
Expansion joints are positioned at or near the point of expected movement of pipe sections. This positioning allows for easy access in the event of a maintenance or repair, and ensures that the expansion joint will be able to perform as designed in all directions. The expansion joint’s location also affects the installation and maintenance costs of adjacent piping, equipment, and buildings. The ideal placement of an expansion joint will result in a location that offers suitable movement allowances, appropriate ambient cooling and simple accessibility.
Generally, an expansion joint is installed between the flanges of two adjacent pipe sections. Larger expansion joints are often sent fully constructed and inserted between the flanges, or constructed on site to facilitate rapid installation. In the latter case, it is important to make sure that the mounting flanges are not too close together or there will be excessive stress at the joint.
If the flanges of an expansion joint are too close, a lubricant is applied to reduce the friction between the flanges. For high-pressure applications, a special metal-to-metal seal is sometimes provided to provide an additional layer of protection.
The addition of arches or bends to the bellows in an expansion joint increases its capacity to withstand lateral and angular movements. This is because it decreases the distance between the flanges of the adjacent pipe sections and allows for more gradual flexing. Achieving this is especially important for larger-diameter expansion joints.
Expansion joints are a vital part of many projects. They help to prevent costly damage from seismic activity and wind loads on structures of all types. A properly sized, designed and fitted expansion joint can last for the life of a project. It is also important to perform routine inspections to keep on top of wear indicators. Performing this type of maintenance will minimize the risk of failure, and will enable the expansion joint to function as intended during its service life.