Metal bellows expansion joint

The Metal bellows expansion joint adopts an elbow structure, on the one hand to reduce the pressure of the system; on the other hand, to prevent the erosion of the balanced expansion joint by high-speed airflow. This kind of expansion joint cannot absorb the axial and lateral thermal displacement reaction force from the pipe system. Its working principle is as follows:

The internal pressure thrust acts on the equipment balance expansion joint and the main balance expansion joint at the same time, in the opposite direction, and the connecting rod replaces the expansion joint to bear the internal pressure pulling force, so that the equipment as a whole is like a "rigid body", and the internal pressure will no longer affect the fixed fulcrum ( The support) generates thrust. Because the two sets of expansion joints have the same balance diameter, they are always in a balanced state no matter how the internal pressure changes.

The axial thermal displacement from the piping system compresses (or stretches) the main bellows, and transmits it to the balance expansion joint through the tie rods, so that the balance expansion joint stretches (or compresses). The force that the seat bears is the sum of the reaction force of the balance expansion joint and the axial thermal displacement spring of the main expansion joint.

　The equivalent axial displacement, bending moment and shear force of the transverse thermal displacement on the main expansion joint are exactly the same as the compound corrugated expansion joint. When the tie rod is thermally displaced in the transverse direction of the expansion joint, it deflects to a certain angle from the original installation state. Since universal nuts (spherical nuts) are used at both ends of the tie rods, which are equivalent to hinge joints and do not transmit bending moments, the balanced expansion joint is not affected by the force of lateral displacement (Note: the nut on the other side of the tie rod plate where the universal nut is installed , Lock it at the manufacturer, and after the expansion joint is installed on-site, it must be loosened).

The exhaust gas pipelines of steam turbine outlets at home and abroad have strict requirements on the thrust and pressure drop of the expansion joints, and this structure is often used. But it is not suitable for working conditions with high dust content in the airflow, because dust particles will exist in the inner cavity of the balance expansion joint, block the pores, and cause the balance expansion joint to fail.