Page 94 - Pressure Vessel Design Manual

General Design 75

11. General. 16. Ligaments.
Reinforcement should be calculated in the corroded When there is a series of closely spaced openings in a
condition assuming maximum tolerance (minimum t). vessel shell and it is impractical to reinforce each
For non x-rayed vessels, t, must be computed using a opening, the construction is acceptable, provided
stress value of 0.8s [l, Section UG-37(a)]. the efficiency of the ligaments between the holes is
acceptable [l, Section UG-531.

12. Openings through seam. [l, Section UW-141. 17. Multiple openings. [l, Section UG-421.
a. Openings that have been reinforced may be located a. For two openings closer than 2 times the average
in a welded joint. E =joint efficiency of seam for diameters and where limits of reinforcement over-
reinforcement calculations. ASME Code, Division lap, the area between the openings shall meet the
1, does not allow a welded joint to have two differ- following:
ent weld joint efficiencies. Credit may not be taken e Must have u combined urea equal to the sum of
for a localized x-rayed portion of a spot or non x- the two areas.
rayed seam. e No portion of the cross-section shall apply to
b. Small nozzles that are not required to be checked more than one opening.
per the Code can be located in circumferential a Any overlap area shall be proportioned between
joints providing the seam is x-rayed for a distance the two openings by the ratio of the diameters.
three times the diameter of the opening with the e Ifthe area between the openings is less than SO%
center of the hole at midlength. of that required for the two openings, the
supplemental rules of Pura. 1-7(a) and (c) shall
apply.
13. Re-pads over seam. b. When more than two openings are to be provided
If at all possible, pads should not cover weld seams. with combined reinforcement:
When unavoidable, the seam should be ground flush e The minimum distance between the centers is 1 ?$
before attaching the pad [l, Section UG-821. the average diameters.
e The area of reinforcement between the two noz-
zles shall be at least 50% of the urea required for
14. Openings near seams. the two openings.
Small nozzles (for which the Code does not require c. For openings less than 12 times the average dia-
the reinforcement to be checked) shall not be located meters:
closer than 1/2 in. to the edge of a main seam. When e No credit may be taken for the area between the
unavoidable, the seam shall be x-rayed, per ASME openings.
Code, Section UW-51, a distance of one and a half e These openings shall be reinforced as in (d).
times the diameter of the opening either side of the d. Multiple openings may be reinforced as an opening
closest point [I, Section UW-141. equal in diameter to that of a circle circumscribing
the multiple openings.

18. Plane of reinforcement.
15. External pressure. A correction factor f may be used for “integrally re-
Reinforcement required for openings subject to exter- inforced’ nozzles to compensate for differences in
nal pressure only or where longitudinal compression stress from longitudinal to circumferential axis of
governs shall only be 50% of that required for internal the vessel. Values off vary from 1.0 for the longitu-
pressure and t, is thickness required for external pres- dinal axis to 0.5 for circumferential axis [I, Section
sure [l, Section UG-37(d) ].
UG-371.