001 B

Figure 5-22. Bending moment in a cylinder due to circumferential moment on an external attachment. (Reprinted by permission from the Welding Research Council.)


1. Figure 5-15 should be used if the vessel is in brittle (low temperature) or fatigue service. For brittle fracture the maximum tensile stress is governing. The stress concentration factor is applied to the stresses which are perpendicular to the change in section.

2. Subscripts 0 and C indicate circumferential direction, X and L indicate longitudinal direction.

3. Only rectangular shapes where C1/C2 is between \ and 4 can be computed by this procedure. The charts and graphs are not valid for lesser or greater ratios.

4. Methods of reducing stresses from local loads:

a. Add reinforcing pad.

b. Increase shell thickness.

c. Add partial ring stiffener.

d. Add circumferential ring stiffener(s).

e. Kneebrace to reduce moment loads.

f. Increase attachment size.

5. See Procedure 5-3 to convert irregular attachment shapes into suitable shapes for design procedure.

6. For radial loads the stress on the circumferential axis will always govern.

7. The maximum stress due to a circumferential moment is 2-5 times larger than the stress due to a longitudinal moment of the same magnitude.

8. The maximum stress from a longitudinal moment is not located on the longitudinal axis of the vessel and may be 60°-70° off the longitudinal axis. The reason for the high stresses on or adjacent to the circumferential axis is that, on thin shells, the longitudinal axis is relatively flexible and free to deform and that the loads are thereby transferred toward the circumferential axis which is less free to deform. Figures 5-18, 5-19, and 5-20 do not show maximum stresses since their location is unknown. Instead the stress on the longitudinal axis is given.

9. For attachments with reinforcing pads-. This applies only to attachments that are welded to a reinforcing plate that is subsequently welded to the vessel shell. Attachments that are welded through the pad (like nozzles) can be considered as integral with the shell.

Moment loadings for nonintegral attachments must be converted into radial loads. This will more closely approximate the manner in which the loads are distributed in shell and plate. Stresses should be checked at the edge of attachment

Table 5-13

Computing Stresses

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