Flanged and Ducted Bellows may be the right answer to pipe, duct and vessel thermal growth problems compared to conventional thin-walled metal bellows.

The advantages of a heavy convolution (up to 1/2 “thick) is its ability to resist mechanical damage. Dents and gouges create stress rises in the thin bellows that result in fatigue cracks over time. Cracks of any type are very difficult to weld the repair on thin bellows (typically 0.06 “or thinner walls), but can be performed by plant maintenance personnel on heavy wall bellows. The thicker wall also better resists corrosion attacks; An added benefit is the common use of carbon steel material that is almost never used in thinner bellows rather than stainless steel or nickel alloys. Drain couplings can also be added to the bottom of the flanged convolution and conduit to prevent condensate build-up.

The most common application for flanged and ducted expansion joints is ASME code heat exchangers, and they are the preferred bellows of choice as movement is exclusively axial. The thick-walled deep gyrus is durable and should last the life of the exchanger. The downside to the heavy wall design is the increased stiffness that can overload the heat exchanger tube plate.

Many engineering companies have prohibited the use of thin-walled bellows expansion joints in process piping due to fear of improper applications in the field that could result in failure. With a flanged and ducted bellows, those fears are unfounded, as the heavy wall is as foolproof an expansion joint as can be expected.