A movement joint or expansion joint is basically an assembly specially designed to hold different sections in a system together, absorb vibration and the temperature-induced contraction or expansion of construction materials, as well as allow movement caused by earthquakes or ground settlement. They are widely used between parts of bridges, buildings, railway tracks, sidewalks, ships, piping systems, and other structures. In most piping systems, both rubber and metal expansion joints can be used to relieve stress and keep a flange gasket from being crushed. But which type is better for your specific needs? Let’s take a look at the benefits of each type and decide which one you should use in your piping system.

1. Advantages of metal expansion joints

– Temperature

Rubber movement joints with standard materials and construction have an upper temperature ranging from only 230 �F (110 �C) to 400 �F (204 �C). Metal movement joints, on the other hand, do come with a far broader range, from -400 �F (-240 �C) to 1800 �F (982 �C). However, at higher temperatures, working pressures are often reduced.

– Pressure

The strength of metals is obviously an advantage over rubber materials in high-pressure environments. Depending on diameter, rubber expansion joints can typically have the pressure capability up to 245 psi with a full vacuum rating, while metal movement joints might be constructed for pressures up to 950 psi. Nevertheless, the relative spring rates and stiffness combined with thrust forces must be examined carefully. Anchors and piping systems should be specially designed to handle this combined load.

2. Advantages of rubber expansion Joints

– Movement

Metal and rubber movement joints have relatively similar movement capability in the axial plane (extension and compression). However, rubber joints are obviously able to absorb a greater amount of lateral movement in comparison with metal models that have a similar face-to-face dimension. Constructions, either universal or dual, are still available for metal models in which large movements are required in the lateral plane, but these are quite costly and need to be considered carefully depending on usage.

– Fatigue or cycle life

The fatigue or cycle life of an expansion joint is basically influenced by many factors, including pressure, temperature, vibration, movement, and the initial design of the joint itself. While metal models are often susceptible to fatigue problems due to excessive movement or cycling, rubber joints are made of resilient elastomers to work as a vibration dampener, which is free from cycle or fatigue failure.

– Installation and maintenance

Rubber movement joints don’t require additional gaskets and can be easily installed by 1 or 2 people without the need for special handling tools. Metal models must be occasionally serviced to ensure that the flange gasket hasn’t deteriorated.

Final verdict

Overall, metal movement joints are used more frequently than rubber joints mainly because common application conditions, including pressures and temperatures, favor their usage. Though rubber joints cannot replace metal ones in all cases, they are still a better option for some projects involving sound dampening and high vibration. Consult with a trusted manufacturer to make sure the chosen products can meet your specific needs.