Dual Gimbal - CAESAR II - Reference Data

CAESAR II Applications Guide

Reference Data

Dual gimbal joints are two, usually angular-only, gimbaled joints in series in the pipeline. Putting two (or three) angular-only gimbaled joints together provides the ability to absorb lateral and possibly axial deformation.

Pipe flexibility software is unable to model the axial-only component of the possible deformation because it requires large rotation of the expansion joint components.

Use the single angular deformation only gimbals in series with at least one other gimbaled joint. It is only in series that the angular deformation only gimbal provides for any lateral movement.

Gimbaled joints are designed to take pressure thrust. Verify that the joint manufacturer is aware of the design loads on the gimbal. Model each individual angular-only gimbal joint as a zero length expansion joint with rigid axial, transverse, and torsional stiffnesses. Ensure that the bending stiffness is equal to the manufacturer's published rotational stiffness term.

The minimum required distance, or L, between adjacent single gimbaled joints (shown as 8-7 in the following example) is principally a function of the angular and rotational deformation to be absorbed, the diameter, and the number of convolutions per joint. The following figure shows a dual gimbal comprised of two angular-only gimbals. The bending stiffness for each gimbaled joint is 490.0-inches lb./deg.

Because both expansion joints use the same stiffness values, it is shown only once in this example.