At present, there are two main types of expansion joints: rubber expansion joints and metal corrugated expansion joints. With reference to different working conditions and applications, the advantages and disadvantages of rubber expansion joints and metal corrugated expansion joints are compared and analyzed, and some suggestions on how to select expansion joints are put forward:
（1） Structural comparison
The metal corrugated expansion joint contains one or more corrugated pipes, which are mainly made of stainless steel metal materials, and are used to absorb various devices with dimensional changes caused by thermal expansion and cold contraction of pipelines and equipment.
The rubber expansion joint belongs to a kind of non-metallic compensator. Its materials are mainly fiber fabrics, rubber and other materials, which can compensate the vibration caused by the operation of fans and air ducts and the axial, transverse and angular deformation caused by pipes.
（2）Comparison of pressure and thrust
The pressure thrust is the pressure effect transmitted by a flexible unit (such as bellows) that is installed in a rigid piping system with pressure.
The rubber expansion joint has no reverse thrust effect on the equipment and system. For metal corrugated expansion joints, this force is a function of the system pressure and the average diameter of the corrugated pipe. When the system pressure is high or the pipe diameter is large, the pressure thrust is very large. If not properly constrained, the corrugated pipe itself or the equipment nozzle will be damaged, and even the fixed fulcrums at both ends of the system will be greatly damaged.
（3）Flexible comparison
The inherent characteristics of rubber expansion joints make them much more flexible than metal corrugated expansion joints.
（4）Displacement comparison
The rubber expansion joint absorbs large displacement per unit length, which can provide large multi-dimensional compensation in a small size range.
When absorbing the same displacement as the rubber expansion joint, the metal corrugated expansion joint needs a large space, and the use of a metal corrugated expansion joint cannot meet the horizontal, axial and angular displacement at the same time.
（5）Installation comparison
The rubber expansion joint is easy to install and replace, without strict alignment, and can adapt to the misalignment of pipeline. Because the system error is unavoidable in the pipe connection, the rubber expansion energy saving installation error is better. However, the metal corrugated expansion joints are strictly limited in size during installation due to the large rigidity of metal materials.
（6）Adaptability comparison
The rubber expansion joint can be made into any shape and any circumference.
The metal corrugated expansion joint has no good adaptability.
（7）Comparison of vibration isolation, sound insulation and heat insulation effects
The rubber expansion joint is close to zero vibration transmission.
The metal corrugated expansion joint can only reduce the vibration intensity.
In terms of sound insulation and heat insulation, rubber expansion joints are also stronger than metal corrugated expansion joints.
（8）Corrosivity comparison
The rubber expansion joint is usually made of EPDM, neoprene, rubber, etc. These materials are corrosive.
For metal bellow expansion joints, if the selected bellow material is not suitable for the flow medium of the system, the corrosivity of the expansion joint will be reduced. Chlorine ion penetrated from the thermal insulation layer is often the cause of corrosion of stainless steel bellow.
The two expansion joints have their own advantages and disadvantages. In actual use, they can be selected according to the actual working conditions. At present, the domestic metal corrugated expansion joints have been fully developed, and the development history is far longer than that of rubber expansion joints, with good quality.
Post time: Oct-19-2022
