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Multiply Bellows - The multiple benefits

The Principle

The most important feature of PEBIFLEX expansion joints is the multi-ply structure of the bellows elements. The bellows are manufactured as multi-layered tube  of plies ranging in number from 2 to 20 depending up on diameter and specified operating pressure.

Each of the thin layer acts as a nearly neutral fiber which offer significantly lower resistance to movements in the piping system than a single wall bellows. Significantly less force is required for actuating multiply bellows.

Thus with  the same dimensions PEBIFLEX bellows can accept significantly more movements. The stresses induced on the individual layers of  PEBIFLEX bellows are a fraction of the stresses induced in the single wall bellows of equal thickness. This results in highest possible service life of the PEBIFLEX bellows

The Advantages

• Safety - A catastrophic sudden failure is virtually impossible. The multiply inner core prevents the instantaneous bursting action. If a crack occurs for reasons like stress, corrosion fatigue failure in the inner or outer plies- the plies in between acting as  labyrinth seal contain the pressure and the medium and hold the entire joint intact. A small bubble or blister occurs only in the outer ply. However the joint still performs satisfactorily for many thousands of  cycles giving enough time for the procurement of the replacement.

• Longer Service Life - The inherent advantage of using multiple plies of  relatively thin gauge material results in less residual stresses which are introduced at the time of forming the bellows element . Also the thinner gauge multiple plies are subjected to less operating stresses compared to a single heavy gauge in operating cycles.  For a given duty conditions PEBIFLEX   bellows have lower built-in and operating stresses which ultimately results in longer life.

• Compact Design - Since multiply bellows are having more flexibility than conventional bellows they require less length to accommodate a given movement in the pipelines. This makes the assembly of PEBIFLEX bellows more compact and economical.

• Lower Thrust Forces - The multiply design results in to lower spring rates for a given pressure capacity. Also the effective cross sectional area of multiply bellows is less compared to conventional bellows to accommodate a given movement. These two reductions result in to lower forces and moments on the anchors, equipments and guides supporting the piping system. The anchors and guides of the system can be dimensioned significantly smaller and more economically. This increases the life of the connected equipment and raises the reliability of the overall piping system keeping the piping cost to a minimum.

• Cost Reduction - Because of  higher flexibility and movement capacity, a small number of expansion joints is sufficient to absorb large displacements compared to conventional expansion joints.

• No Emergency - Even if the inner plies gets damaged the PEBIFLEX multiply bellows does not loose its capacity to perform essential functions. Because of the intact outer plies the ability to resist pressure and the flexibitity of the the expansion joints are retained over a longer time. This gives enough time to replace the joint  at the next planned shut-down.

• Economical Design For Corrosion Protection - In order to reach the desired degree of protection only the ply of the bellows actually in contact with the medium is manufactured from special high corrosion  and temperature resistant alloy. the remaining outer plies not in contact with the medium are selected from other economical standard stainless steels.

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