Concentric Toriconical Reducers Discontinuity Stress

At high pressures (over 150 psi), where discontinuity stresses at the cone-to-cylinder junction can reach values above allowable limits, conical reducers having a knuckle radius at the large cylinder and a flare (reintrant knuckle) at the small end are preferred, as shown in Figure 100-13.

Although more expensive to fabricate, toriconical reducers have the advantage of moving the circumferential weld joints away from the high discontinuity stresses, and allowing better fit-up with the cylindrical shells. The knuckles are usually fabricated in the form of toroidal rings of the same plate thickness as the conical section.

The ASME Code specifies only the minimum value for the knuckle radius at the large end (RL), but has no dimensional requirements for the radius at the small end (Rs). In most cases, the same plate thickness is used for the entire reducer and the required radii RL and Rs are determined using the maximum membrane stresses.

Toriconical Reducer Courtesy of the ASME

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