SS bellows is the elastic vessel that can be compressed when pressure is applied to the outside of the vessel, or extended under vacuum. When the pressure or vacuum is released, the bellows will return to its original shape (provided the material has not been stressed past its yield strength).

 Features of bellows

• Economical end usage
• Providing for lower initial costs in piping & construction work

Advantages of bellows

• Reduce vibration
• Dampen sound transmission
• Compensate lateral, torsional & angular movements
• Compensate axial movements
• Minimal face-to-face dimensions
• Lightweight
• Low movement forces required
• Reduced fatigue factor
• Reduced heat loss
• Corrosion, erosion resistant
• No gaskets

Inspection Procedures for Bellows

a. Cracking. (Sun Checking) Cracking, or crazing may not be serious if only the outer cover is involved and the fabric is not exposed. If necessary, repair on site with rubber cement where cracks are minor. Cracking where the fabric is exposed and torn, indicates the expansion joint should be replaced. Such cracking is usually the result of excess extension, angular or lateral movements. Such cracking is identified by: (1) a flattening of the arch (2) cracks at the base of the arch, and/or (3) cracks at the base of the flange. To avoid future problems, replacement expansion joints should be ordered with control rod units.

b. Blisters-Deformation-Ply Separation. Some blisters or deformations, when on the external portions of an expansion joint, may not affect the proper performance of the expansion joint. These blisters or deformations are cosmetic in nature and do not require repair. If major blisters, deformations and/or ply separations exist in the tube, the expansion joint should be replaced as soon as possible. Ply separation at the flange O.D. can sometimes be observed and is not a cause for replacement of the expansion joint.

c. Metal Reinforcement. If the metal reinforcement of an expansion joint is visible through the cover, the expansion joint should be replaced as soon as possible.

d. Dimensions. Any inspections should verify that the installation is correct; that there is no excessive misalignment between the flanges; and, that the installed face-to-face dimension is correct. Check for over-elongation, over-compression, lateral or angular misalignment. If incorrect installation has caused the expansion joint to fall, adjust the piping and order a new expansion joint to fit the existing installation.

e. Rubber Deterioration. If the joint feels soft or gummy, plan to replace the expansion joint as soon as possible.

f. Leakage. If leaking or weeping is occurring from any surface of the expansion joint, except where flanges meet, replace the joint immediately. If leakage occurs between the mating flange and expansion joint, tighten all bolts. If this is not successful, turn off the system pressure, loosen all flange bolts and then retighten bolts in stages by alternating around the flange. Make sure there are washers under the bolt heads, particularly at the split in the retaining rings. Remove the expansion joint and inspect both rubber flanges and pipe mating faces for damage and surface condition. Repair or replace as required. Also, make sure the expansion joint is not over elongated, as this can tend to pull the expansion joint flange away from the mating flange resulting in leakage. If leakage persists, consult the manufacturer for additional recommendations.