Duct work assemblies can include fabricated elbows, tees, straight sections of duct work, fabric or metallic expansion joints and can be rectangular or round.
Heat Exchanger shell bellows are used on fixed tube sheet heat exchangers. Bellows deflection is only axial and can be either extension or compression depending on the differential expansion of shell and tubes. In most cases the tubes are hotter than the shell, moreover tube material is sometimes high alloy, i.e. Stainless steel or nickel alloy, which expands about 50% more than carbon steel.