Metal Bellows Archives - Bellows Systems

What are Multi Ply Metal Bellows and where are they used?

Multi-ply bellows are made up of a multiple telescoping tube (or plys) of sheet metal. The telescoping tubes are formed (Expanded mandrel or hydraulic) together to form each convolution.

Why are they better than single-ply bellows?
  • They offer redundance in the event of inner ply failure.
  • The offer much lower stiffness.
  • Leak detection measures can be incorporated to detect ply failure hence providing time to change out the existing expansion joint.
  • Much higher cycle life per corrugation.
  • Corrugated length can be much shorter to achieve similar movement and cycle life performance to that of a single ply bellows.
What are the drawbacks?
  • They have higher meridional bending stress.
  • They have less resilience to corrosion due to the individual wall thickness.
  • Higher ply count can result in slightly higher manufacturing cost.
  • Increased in-plane and column instability compared to a similar single ply construction.
  • Difficult to repair in the field due to the much thinner ply thickness.
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What are Single Ply Metal Bellows and where are they used?

Single ply bellows are made up of a single tube (or ply) of sheet metal of a defined thickness.

Why are they better than multi-ply bellows?
  • The Expansion joint offers a simple construction and lower manufacturing.
  • They offer a higher pressure capacity compared to multi-ply expansion joints of a similar combined thickness
  • They more stable and less susceptible to in-plane and column squirm.
  • They are more resilient to corrosion due to their thicker wall.
What are the drawbacks?
  • They are generally stiffer than multi-ply bellows, which means they need more axial force per unit compression.
  • They have lower cycle life compared to a multi-ply bellows of similar wall thickness.
  • Preventive leak detection is not possible in many cases.
  • Longer convoluted lengths / taller convolutions are required compared to multi-ply bellows to provide similar movement compared to multi-ply bellows.
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