Page 93 - Pressure Vessel Design Manual

74 Pressure Vessel Design Manual

PROCEDURE 2-14

NOZZLE REINFORCEMENT

The following are only guidelines based on Section VIII, 5. Forming.
Division 1 of the ASME Code [l]. This is not an attempt to Reinforcing pads should be formed as closely to the
cover every possibility nor is it to become a substitute for contour of the vessel as possible. While normally put
using the Code. on the outside of the vessel, re-pads can also be put
inside providing they do not interfere with the vessel’s
1. Limits. operation [I, Section UG-821.
a. No reinforcement other than that inherent in the
construction is required for nozzles [ 1, Section
UG-36(c) (3)]: 6. Tell-tale holes.
0 3-in. pipe size and smaller in vessel walls 3/8-in. Reinforcing pads should be provided with a U4-in.
and less. tapped hole located at least 45” off the longitudinal
0 %in. pipe size and smaller in vessel walls greater center line and given an air-soap suds test [I, Section
than 3/8in. UW-I5(d)].
b. Normal reinforcement methods apply to [I, Section
UG-36(b) (I)]: 7. Elliptical or obround openings.
0 Vessels 60-in. diameter and less--1/2 the vessel When reinforcement is required for elliptical or
diameter but not to exceed 2Oin. obround openings and the long dimension exceeds
0 Vessels greater than 60-in. diameter-113 the twice the short dimension, the reinforcement across
vessel diameter but not to exceed 40 in.
c. For nozzle openings greater than the limits of the short dimension shall be increased to guard
against excessive distortion due to twisting moment
Guideline Ib, reinforcement shall be in accordance
with Para. 1-7 of ASME Code. [l, Section UG-36(a) (I)].

2. Strength. 8. Openings inflat heads.
It is advisable but not mandatory for reinforcing pad Reinforcement for openings in flat heads and blind
material to be the same as the vessel material [I, flanges shall be as follows [I, Section UG-391:
Section UG-411: a. Openings e 112 head diameter-area to be replaced
a. If a higher strength material is used, either in the equals 0.5d (tr), or thickness of head or flange may
pad or in the nozzle neck, no additional credit may be increased by:
be taken for the higher strength. Doubling C value.
b. If a lower strength material is used, either in the pad 0 Using C = 0.75.
or in the nozzle, then the area taken as reinforce- 0 Increasing head thickness by 1.414.
ment must be decreased proportionately by the ratio b. Openings > 1/2 head diameter-shall be designed
of the stress intensity values of the two materials. as a bolted flange connection. See Procedure 2-15.
Weld material taken as reinforcement must also be
decreased as a proportion, assuming the weld mate-
rial is the same strength as the weaker of the two 9. Openings in torispherical heads.
materials joined. When a nozzle opening and all its reinforcement fall
within the dished portion, the required thickness of
3. Thickness. head for reinforcement purposes shall be computed
While minimum thicknesses are given in Reference 1, using M = 1 [I, Section UG-37(a)].
Section UG-IG(b), it is recommended that pads be not
less than 75% nor more than 150% of the part to which IO. Openings in elliptical heads.
they are attached.
When a nozzle opening and all its reinforcement fall
within 0.8D of an elliptical head, the required thick-
4. Width. ness of the head for reinforcement purposes shall be
While no minimum is stated, it is recommended that equal to the thickness required for a seamless sphere
re-pads be at least 2in. wide. of radius K(D) [I, Section UG-37(a)].