Dear Experts,

Please let me know for a single Z plane system,if there is an offset vertical leg inbetween two horizontal leg having intermediate anchor configurations in both the horizontal leg,so on what basis i will decide to provide two single hinge expansion joint with inbetween piping or double hinge expansion joint assembly as a whole including centre pipe spool piece?

Angulation of the convolutions is likely to be your limiting factor. Depending on the lateral movement, the central element of a double hinge unit may or may not be long enough to give an acceptable angle in the convolutions when displaced. Too much angulation and you will need two single hinge units.

Depending on the amount of deformation to accommodate, three hinge EJs may be employed.

Three hinges between two anchors is a very bad idea. It means that the system is no longer a structure, rather it is a mechanism. There will be an infinite range of positions that parts of the system could adopt and Caesar, like any other stress program, will converge on just one of them.

Vick – If you have a simple dog-leg system the traditional solution is a tied universal expansion joint in the vertical leg. However, support of the pipe between the two bellows could be a problem if you’re dealing with large diameter / refractory lined pipe in which case you’d want to use two hinges. You can consult most any EJ manufacturer’s catalog for the rated capacity for tied universal joints. The rotation of the hinge joints is generally limited to less than 5°/each.

MoverZ – I think you have misinterpreted the large rotation problem surrounding three hinge / hinge & gimbal expansion joint systems. You are correct when you state that they are a mechanism, however the system is statically determinate and stable and therefore have a geometrically defined position based upon the pipe movements. Hinge/Gimbal systems are the BEST solution for generating low reaction forces and moments when given large movements and traditionally used around large rotating equipment. Dave Diehl wrote an article in Caesar’s Mechanical Engineering Newsletter , Vol 27 (6/99) which discusses the issue of large rotations in depth for your reference.

Dan Edgar, PE
Principal Engineer
Senior-Flexonics, Pathway Div