Bellows squirm because they have surpassed the critical design pressure limit. This can occur in small diameter bellows with a large number of convolutions.
|Fabric Expansion Joints can withstand up to 3 PSIG (pounds per square inch gauge) or 100″ H20 column (In pressure). If the pressure exceeds this amount, it is best to use a metallic expansion joint.|
In an axial piping system, the expansion joint should be located as close as possible to a main anchor. The first pipe guide should be located at a distance of 4 pipe diameters away from the expansion joint. The second guide should be located a distance of 14 pipe diameters away from the first guide. During installation, the expansion joint should be either welded or flanged into the piping system.
Hydro-test pressure & holding times vary for different design codes. For example, the ASME SEC VIII Div.1 general hydro-test pressure will be 1.3 x design pressure (minor factors may vary for this equation as well) and for piping design codes, the hydro-test pressure will be ASME B31.4,B31.8 1.5 x design pressure.