Metal expansion joints, also known as metallic expansion joints or metal bellows, are flexible components used in piping systems to absorb movements caused by thermal expansion, vibration, or other factors while maintaining the integrity of the system. They are constructed using metal bellows, which provide flexibility and durability.

Here are some specific types of metal expansion joints commonly used in various industries:

1. Axial Expansion Joints: These expansion joints are designed to absorb axial movements along the axis of the pipe, allowing for expansion and contraction without imposing stress on the piping system. They are used in straight runs of piping systems where axial movement is predominant.

2. Lateral Expansion Joints: Lateral expansion joints accommodate lateral movements perpendicular to the axis of the pipe. They are used in applications where pipes need to move sideways due to thermal expansion, seismic activity, or other factors.

3. Angular Expansion Joints: Angular expansion joints allow for angular movements or rotations around the axis of the pipe. They are used in systems where pipes need to change direction or where misalignment occurs due to thermal expansion or other factors.

4. Universal Expansion Joints: Universal expansion joints, also known as double gimbal expansion joints (as mentioned earlier), provide flexibility in multiple directions, including axial, lateral, and angular movements. They consist of two sets of hinges or gimbal connected by a central spool or bellows.

5. Pressure Balanced Expansion Joints: Pressure balanced expansion joints are designed to minimize the forces exerted on the anchors and supports of the piping system. They use an additional bellows section to balance the pressure forces, reducing the loads transmitted to the piping system.

6. Hinged Expansion Joints: Hinged expansion joints consist of a single bellows section with hinge arrangements at both ends. They allow movement in one direction while restraining movement in other directions, making them suitable for applications where movement needs to be controlled.

7. Tied Expansion Joints: Tied expansion joints incorporate tie rods or rods to limit the movement of the bellows under pressure or vacuum conditions. They are used in high-pressure or high-vacuum applications to prevent overextension of the bellows.

These are just a few examples of specific metal expansion joints used in piping systems. Each type is designed to accommodate different types of movements and operating conditions, ensuring the reliability and safety of the overall system. The selection of the appropriate expansion joint depends on factors such as the magnitude and direction of movement, temperature, pressure, and the specific requirements of the application.