Temperature: Rubber joints with standard construction and materials have an upper range to 110°C. Can be offer special constructions up to 200°C. Metal expansion joints do offer a far greater range, from -250°C to +950°C.
Pressure: Rubber joints depending on diameter, can have pressure capabilities up to 15 bar with a full vacuum rating. Metal joints can be designed for pressures up to 100 bar.
Movements: Rubber and metal expansion joints have similar movement capabilities in the axial plane (compression and extension). However, rubber joints are certainly able to absorb greater lateral movements when compared to metal joints that have similar face to face lengths.
Spring Rates: Rubber and metal joints do have similar characteristics in the axial plane for the standard face to face dimensions. Metal joints are much stiffer when subjected to lateral motion and, typically have a lower lateral movement capability.
Acoustical Impedance: Although well designed (multi-ply) metal joints can lower the transmission of visible vibration, they will continue to transmit distracting and/or damaging noise. Rubber joints significantly reduce the undesirable transmission in piping systems. The elastomeric composition of the joint acts as a dampener that absorbs the greatest percentage of perceptible noise and vibration.
Abrasion/Erosion Resistance: Metal joints typically have a wall thickness anywhere between 0.15mm to 2mm. Rubber joints are much thicker, 12mm to over 25mm. The thin construction of metal joints makes them susceptible to erosive chemicals and abrasive liquids and slurries. Rubber joints are highly resistant to abrasion and erosion of all types and outperform metal joints in the applications where these conditions prevail.
Fatigue/Cycle Life: The fatigue life of a metal joint is affected by many factors such as temperature, pressure, movement, vibration and how the joint was initially designed. Typically, metal joints have a defined cycle or fatigue life that can be calculated through various formulas (EJMA). Metal joints frequently succumb to fatigue failure from excessive cycling/movement. Rubber joints on the other hand are constructed of resilient elastomers and the joint itself acts as a vibration dampener, not susceptible to fatigue/cycle failure.
Installation/Maintenance: Rubber joints do not require additional gasketing and, in many cases, are installed without the use of special handling equipment. Metal joints must be serviced occasionally to insure that the flange gasket is still intact and not deteriorated
