Angular joints rotate rather than stretch. Used in pairs or threes, they let a piping system absorb very large movements over long runs while the hardware carries the pressure thrust — so the anchors see almost nothing.
Hinged
A single bellows with hinge plates and pins that constrain it to rotate in one plane only. The pins carry the full pressure thrust. A hinged joint on its own absorbs very little; hinged joints are designed in pairs or sets of three, arranged so the rotations combine to take up movement in a leg of pipe.
Gimbal
The same idea with a two-axis gimbal ring, so the joint rotates in any plane. Used where the piping moves in three dimensions and a single-plane hinge would bind. Like the hinge, the gimbal ring carries the pressure thrust.
Why they are used in systems, not singly
A two-hinge or three-hinge arrangement converts thermal growth in one leg into rotation at two or three points. Because each joint only rotates, and because the hardware takes the thrust, the result is a system that absorbs very large movement with modest anchor loads. It is the standard solution on hot refinery and power-plant lines where the growth is measured in hundreds of millimetres.
| Arrangement | Movement absorbed | Notes |
|---|---|---|
| Two hinges in one plane | Growth in the leg between them | The classic offset-leg solution |
| Three hinges in one plane | Growth in two connected legs | Used where the run turns twice |
| Two gimbals | Three-dimensional movement | Where the pipe route is not planar |
| Gimbal plus hinge | Combined planar and out-of-plane | Complex routes |
Envelope
| Property | Range |
|---|---|
| Nominal diameter | DN50 – DN3000 |
| Bellows material | SS 321, SS 316L standard; Alloy 625 (UNS N06625) for elevated temperature |
| Hardware | Carbon steel or stainless; coated to project corrosivity category |
| Ends | Weld ends or flanges to DIN or ANSI |
| Design basis | EN 14917:2021, EJMA 11th Edition |