Nozzle Reinforcement

The following are only guidelines based on Section VIII, Division 1 of the ASME Code [1]. This is not an attempt to cover every possibility nor is it to become a substitute for using the Code.

1. Limits.

a. No reinforcement other than that inherent in the construction is required for nozzles [1, Section UG-36(c) (3)]:

• 3-in. pipe size and smaller in vessel walls 3/8-in. and less.

• 2-in. pipe size and smaller in vessel walls greater than 3/8 in.

b. Normal reinforcement methods apply to [1, Section UG-36(b) (1)]:

• Vessels 60-in. diameter and less—1/2 the vessel diameter but not to exceed 20 in.

• Vessels greater than 60-in. diameter—1/3 the vessel diameter but not to exceed 40 in.

c. For nozzle openings greater than the limits of Guideline lb, reinforcement shall be in accordance with Para. 1-7 of ASME Code.

2. Strength.

It is advisable but not mandatory for reinforcing pad material to be the same as the vessel material [1, Section UG-41]:

a. If a higher strength material is used, either in the pad or in the nozzle neck, no additional credit may be taken for the higher strength.

b. If a lower strength material is used, either in the pad or in the nozzle, then the area taken as reinforcement must be decreased proportionately by the ratio of the stress intensity values of the two materials. Weld material taken as reinforcement must also be decreased as a proportion, assuming the weld material is the same strength as the weaker of the two materials joined.

3. Thickness.

While minimum thicknesses are given in Reference 1, Section UG-16(b), it is recommended that pads be not less than 75% nor more than 150% of the part to which they are attached.

While no minimum is stated, it is recommended that re-pads be at least 2 in. wide.

5. Forming.

Reinforcing pads should be formed as closely to the contour of the vessel as possible. While normally put on the outside of the vessel, re-pads can also be put inside providing they do not interfere with the vessel's operation [1, Section UG-82],

6. Tell-tale holes.

Reinforcing pads should be provided with a 1/4-in. tapped hole located at least 45° off the longitudinal center line and given an air-soap suds test [1, Section UW-15(d)].

7. Elliptical or obround openings.

When reinforcement is required for elliptical or obround openings and the long dimension exceeds twice the short dimension, the reinforcement across the short dimension shall be increased to guard against excessive distortion due to twisting moment [1, Section UG-36(a) (1)].

8. Openings in flat heads.

Reinforcement for openings in flat heads and blind flanges shall be as follows [1, Section UG-39]:

a. Openings < 1/2 head diameter—area to be replaced equals 0.5d (tr), or thickness of head or flange may be increased by:

• Increasing head thickness by 1.414.

b. Openings > 1/2 head diameter—shall be designed as a bolted flange connection. See Procedure 2-15.

Openings in torispherical heads. When a nozzle opening and all its reinforcement fall within the dished portion, the required thickness of head for reinforcement purposes shall be computed using M = 1 [1, Section UG-37(a)].

10. Openings in elliptical heads.

When a nozzle opening and all its reinforcement fall within 0.8D of an elliptical head, the required thickness of the head for reinforcement purposes shall be equal to the thickness required for a seamless sphere of radius K(D) [1, Section UG-37(a)].

11. General.

Reinforcement should be calculated in the corroded condition assuming maximum tolerance (minimum t). For non x-rayed vessels, tr must be computed using a stress value of'0.8S [1, Section UC,-37(a)].

12. Openings through seams. [1, Section UW-14].

a. Openings that have been reinforced may be located in a welded joint. E= joint efficiency of seam for reinforcement calculations. ASME Code, Division 1, does not allow a welded joint to have two different weld joint efficiencies. Credit may not be taken for a localized x-rayed portion of a spot or non x-rayed seam.

b. Small nozzles that are not required to be checked per the Code can be located in circumferential joints providing the seam is x-rayed for a distance three times the diameter of the opening with the center of the hole at midlength.

13. Re-pads over seams.

If at all possible, pads should not cover weld seams. When unavoidable, the seam should be ground flush before attaching the pad [1, Section UG-82],

14. Openings near seams.

Small nozzles (for which the Code does not require the reinforcement to be checked) shall not be located closer than 1/2 in. to the edge of a main seam. When unavoidable, the seam shall be x-rayed, per ASME Code, Section UW-51, a distance of one and a half times the diameter of the opening either side of the closest point [1, Section UW-14],

15. External pressure.

Reinforcement required for openings subject to external pressure only or where longitudinal compression governs shall only be 50% of that required for internal pressure and tr is thickness required for external pressure [1, Section UG-37(d) ].

16. Ligaments.

When there is a series of closely spaced openings in a vessel shell and it is impractical to reinforce each opening, the construction is acceptable, provided the efficiency of the ligaments between the holes is acceptable [1, Section UG-53],

17. Multiple openings. [1, Section UG-42], a. For two openings closer than 2 times the average diameters and where limits of reinforcement overlap, the area between the openings shall meet the following:

• Must have a combined area equal to the sum of the two areas.

• No portion of the cross-section shall apply to more than one opening.

• Any overlap area shall be proportioned betioeen the two openings by the ratio of the diameters.

• If the area between the openings is less than 50% of that required for the two openings, the supplemental rules of Para. l-7(a) and (c) shall apply.

b. When more than two openings are to be provided with combined reinforcement:

• The minimum distance between the centers is 1 % the average diameters.

• The area of reinforcement between the two nozzles shall be at least 50% of the area required for the two openings.

c. For openings less than I/3 times the average diameters:

• No credit may be taken for the area between the openings.

• These openings shall be reinforced as in (d).

d. Multiple openings may be reinforced as an opening equal in diameter to that of a circle circumscribing the multiple openings.

18. Plane of reinforcement.

A correction factor f may be used for "integrally reinforced" nozzles to compensate for differences in stress from longitudinal to circumferential axis of the vessel. Values of f vary from 1.0 for the longitudinal axis to 0.5 for circumferential axis [1, Section UG-37],

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Responses

  • camelia grubb
    What is reinforcement in pressure vessel?
    2 years ago
  • viviano
    What are reinforcement pad in pressure vessels?
    2 years ago
  • Dawit
    Why RF pad required on pressure vessle?
    2 years ago
  • Carson
    Why nozzle teinforcement required?
    2 years ago
  • aatifa
    Why nozzle reinforcemnet is required?
    2 years ago
  • ensio
    What is renfircement of nozzel?
    2 years ago

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