Basic Types of Expansion Joints
Basics of Expansion Joints
Piping and ducting systems are always under strain due to thermal expansion and mechanical growth. Thermal expansion happens when materials expand or contract with changes in temperature. Mechanical growth is the result of pressure surges during system startup or shutdown. The stiffness of pipes and connections prevents these movements without causing undue stress on the materials. Over time, this stress can lead to wear and tear, eventually causing the failure of mechanical components in the piping system. Replacing parts in a piping system can be very expensive. Thus, expansion joints are used to accommodate these movements and help manage the stress within a replaceable component. Expansion joints come in various forms and materials.
Rubber Expansion Joints
Rubber expansion joints are a cost-effective method for providing protection and managing motion in a specific area. These joints are made from different grades of polymers, with some being more common. The choice of polymer or rubber depends on the application’s internal and external conditions. For example, ethylene propylene diene monomer (EPDM) is a popular material for expansion joints but is not suitable for use with hydrocarbon-based media. Therefore, neoprene is the preferred material for expansion joints when dealing with oils, gasoline, and other petroleum-based fluids. Choosing the right polymer is crucial for the longevity of the expansion joint.
Metal Bellows Expansion Joints
In some cases, systems require more than what rubber expansion joints can handle. This is often the case when dealing with systems that need to accommodate large movements, high temperatures, or pressures beyond the capabilities of rubber. Metal bellows expansion joints provide greater flexibility in terms of pressure and temperature, as well as resistance to certain substances, while still protecting the system by isolating the movements and vibrations within the expansion joint. These joints are made from high-quality metals, including various grades of stainless steel and some exotic metals like Inconnel® and Monel®. They can be constructed with single or double bellows and are available in different installation methods, such as weld in nipples, fixed flanges, floating or Van Stone flanges, and raised face flanges. Configurations can include dual bellows and externally pressurized bellows
Fabric Expansion Joints
For applications that demand extensive movement, high temperatures, and low pressures, fabric expansion joints are the perfect solution. Ducting systems in power plants, concrete facilities, and other industries deal with high-temperature gases at low pressures. Fabric expansion joints, made with steel frames and advanced belts, are designed to handle large movements and high temperatures while keeping the system contained. Fabric expansion joints come in various frame designs and belt configurations. The choice of belt depends on the application’s external and internal conditions, similar to rubber expansion joints.
PTFE Expansion Joints
PTFE, or commonly referred to as TEFLON™ expansion joints can be combined with metal or rubber expansion joints to enhance the functionality of the joints. Many of the chemical resistant properties of the PTFE make these ideal for acidic or caustic media.
