(E) towers, building frames, tanks, mechanical equipment, instruments, and foundations
104.1.3 Straight Pipe Under External Pressure. For determining wall thickness and stiffening requirements for straight pipe under external pressure, the procedures outlined in UG-28, UG-29, and UG-30 of Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code shall be followed.
104.2 Curved Segments of Pipe
104.2.1 Pipe Bends. Pipe bends shall be subject to the following limitations:
(A) The minimum wall thickness shall meet the requirements of para. 102.4.5 and the fabrication requirements of para. 129.
(B) Limits on flattening and buckling at bends may be specified by design, depending upon the service, the material, and the stress level involved. Where limits on flattening and buckling are not specified by design, the requirements of para. 129.1 shall be met.
104.2.2 Elbows. Elbows manufactured in accordance with the standards listed in Table 126.1 are suitable for use at the pressure-temperature ratings specified by such standards, subject to the requirements of para. 106.
104.3 Intersections
104.3.1 Branch Connections
(A) This paragraph gives rules governing the design of branch connections to sustain internal and external pressure in cases where the axes of the branch and the run intersect, and the angle between the axes of the branch and of the run is between 45 deg and 90 deg, inclusive.
Branch connections in which the smaller angle between the axes of the branch and the run is less than 45 deg or branch connections where the axes of the branch and the run do not intersect impose special design and fabrication problems. The rules given herein may be used as a guide, but sufficient additional strength must be provided to assure safe service. Such branch connections shall be designed to meet the requirement of para. 104.7.
(B) Branch connections in piping may be made from materials listed in Appendix A by the use of the following:
(B.1) fittings, such as tees, laterals, and crosses made in accordance with the applicable standards listed in Table 126.1 where the attachment of the branch pipe to the fitting is by butt welding, socket welding, brazing, soldering, threading, or by a flanged connection.
(B.2) weld outlet fittings, such as cast or forged nozzles, couplings and adaptors, or similar items where the attachment of the branch pipe to the fitting is by butt welding, socket welding, threading, or by a flanged connection. Such weld outlet fittings are attached to the run by welding similar to that shown in Fig. 127.4.8 (E) or Fig. 127.4.8 (F), as applicable. MSS SP-97 may be used for design and manufacturing standards for integrally reinforced forged branch outlet fittings. Couplings are restricted to a maximum of NPS 3.
(B.3) extruded outlets at right angles to the run pipe, in accordance with (G) below, where the attachment of the branch pipe is by butt welding.
(B.4) piping directly attached to the run pipe by welding in accordance with para. 127.4.8 or by socket welding or threading as stipulated below:
(B.4.1) socket welded right angle branch connections may be made by attaching the branch pipe directly to the run pipe provided.
(B.4.1.1) the nominal size of the branch does not exceed NPS 2 or one-fourth of the nominal size of the run, whichever is smaller.
(B.4.1.2) the depth of the socket measured at its minimum depth in the run pipe is at least equal to that shown in ASME B16.11. If the run pipe wall does not have sufficient thickness to provide the proper depth of socket, an alternate type of construction shall be used.
(B.4.1.3) the clearance between the bottom of the socket and the end of the inserted branch pipe is in accordance with Fig. 127.4.4(C).
(B.4.1.4) the size of the fillet weld is not less than 1.09 times the nominal wall thickness of the branch pipe.
(B.4.2) threaded right angle branch connections may be made by attaching the branch pipe directly to the run provided
(B.4.2.1) the nominal size of the branch does not exceed NPS 2 or one-fourth of the nominal size of the run, whichever is smaller.
(B.4.2.2) the minimum thread engagement is: 6 full threads for NPS ½ and NPS ¾ branches; 7 for NPS 1, NPS 1¼, and NPS 1½ branches; and 8 for NPS 2 branches. If the run pipe wall does not have sufficient thickness to provide the proper depth for thread engagement, an alternative type of construction shall be used.
(C) Branch Connections Not Requiring Reinforcement. A pipe having a branch connection is weakened by the opening that must be made in it. Unless the wall thickness of the branch and/or run pipe is sufficiently in excess of that required to sustain the pressure, it is necessary to provide additional material in order to meet the reinforcement requirements of (D) and (E) below. However, there are certain branch connections for which supporting calculations are not required. These are as follows:
(C.1) branch connections made by the use of a fitting (tee, lateral, cross, or branch weld-on fitting), manufactured in accordance with a standard listed in Table 126.1, and used within the limits of pressure-temperature ratings specified in that standard.
(C.2) branch connections made by welding a coupling or half coupling directly to the run pipe in accordance with Fig. 127.4.8(E), provided the nominal diameter of the branch does not exceed NPS 2 or one-fourth the nominal diameter of the run, whichever is less. The minimum wall thickness of the coupling anywhere in the reinforcement zone (if threads are in the zone, wall thickness is measured from the root of the thread to the minimum O.D.) shall not be less than that of the unthreaded branch pipe. In no case shall the thickness of the coupling be less than extra heavy or Class 3000 rating.
Small branch connections NPS 2 or smaller as shown in Fig. 127.4.8(F) may be used, provided tw is not less than the thickness of schedule 160 pipe of the branch size.
(C.3) integrally reinforced fittings welded directly to the run pipe when the reinforcements provided by the fitting and the deposited weld metal meets the requirements of (D) below.
(C.4) integrally reinforced extruded outlets in the run pipe. The reinforcement requirements shall be in accordance with (G) below.
(D) Branch Connections Subject to Internal Pressure Requiring Reinforcement
(D.1) Reinforcement is required when it is not provided inherently in the components of the branch connection. This paragraph gives rules covering the design of branch connections to sustain internal pressure in cases where the angle between the axes of the branch and of the run is between 45 deg and 90 deg. Subparagraph (E) below gives rules governing the design of connections to sustain external pressure.
(D.2) Figure 104.3.1(D) illustrates the notations used in the pressure-temperature design conditions of branch connections. These notations are as follows:
b = subscript referring to branch
Do = outside diameter of pipe, in. (mm)
d1 = inside centerline longitudinal dimension of the finished branch opening in the run of the pipe, in. (mm)
= [Dob -2(Tb -A)]/sin á
d2 = “half width" of reinforcing zone, in. (mm)
= the greater of d1 or
(Tb -A) + (Th -A) + d1/2 but in no case more than Doh, in. (mm)
h = subscript referring to run or header
L4 = altitude of reinforcement zone outside of run, in. (mm)
= 2.5(Tb -A) + tr or 2.5
(Th -A), whichever is smaller
tr = thickness of attached reinforcing pad, in Example A, in. (mm); or height of the largest 60 deg right triangle supported by the run and branch outside diameter projected surfaces and lying completely within the area of integral reinforcement, in Example B, in. (mm)
Tb, Th = actual (by measurement), or minimum wall thickness of the branch or header pipe, in. (mm), permissible under purchase specification
tmb, tmh = required minimum wall thickness, in. (mm), of the branch or header pipe as determined by use of eq. (3) or (3A) in para. 104.1.2(A)
a = angle between axes of branch and run, deg
(D.2.1) If the run pipe contains a longitudinal seam which is not intersected by the branch, the stress value of seamless pipe of comparable grade may be used to determine the value of tmh for the purpose of reinforcement calculations only. If the branch intersects a longitudinal weld in the run, or if the branch contains a weld, the weld joint efficiency for either or both shall enter the calculations. If the branch and run both contain longitudinal welds, care shall be taken to ensure that the two welds do not intersect each other.
(D.2.2) The required reinforcement area in square inches (square millimeters) for branch connections shall be the quantity
A7 = A6(2 - sin a) = (tmh - A)d1 (2 - sin a)
For right angle connections the required reinforcement becomes
A7 = A6 = (tmh – A)d1
The required reinforcement must be within the limits of the reinforcement zone as defined in (D.2.4) below.
(D.2.3) The reinforcement required by (D.2) shall be that provided by any combination of areas A1
, A2, A3, A4, and A5
, as defined below and illustrated in Fig. 104.3.1(D) where
A1 = area provided by excess pipe wall in the run
= (2d2 – d
1)(Th - tmh)
A2 = area, in.2 (mm2), provided by excess pipe wall in the branch for a distance L4 above the run
= 2L4 (Tb - t
mb)/sin a
A3 = area provided by deposited weld metal beyond the outside diameter of the run and branch, and for fillet weld attachments of rings, pads, and saddles
A4 = area provided by a reinforcing ring, pad, or integral reinforcement. The value of A4 may be taken in the same manner in which excess header metal is considered, provided the weld completely fuses the branch pipe, run pipe, and ring or pad, or integral reinforcement. For welding branch connections refer to para. 127.4.8.
A5 = area provided by a saddle on right angle connections
= (O.D. of saddle - Dob)tr
A6 = pressure design area expected at the end of service life
= (tmh - A)d1
Portions of the reinforcement area may be composed of materials other than those of the run pipe, but if the allowable stress of these materials is less than that for the run pipe, the corresponding calculated reinforcement area provided by this material shall be reduced in the ratio of the allowable stress being applied to the reinforcement area. No additional credit shall be taken for materials having higher allowable stress values than the run pipe.
(D.2.4) Reinforcement Zone. The reinforcement zone is a parallelogram whose width shall extend a distance d
2 on each side of the centerline of the branch pipe, and whose altitude shall start at the inside surface of the run pipe and extend to a distance L4 from the outside surface of the run pipe.
(D.2.5) Reinforcement of Multiple Openings. It is preferred that multiple branch openings be spaced so that their reinforcement zones do not overlap. If closer spacing is necessary, the following requirement shall be met. The two or more openings shall be reinforced in accordance with (D.2), with a combined reinforcement that has a strength equal to the combined strength of the reinforcement that would be required for the separate openings. No portion of the cross section shall be considered as applying to more than one opening, or be evaluated more than once in a combined area.
When more than two adjacent openings are to be provided with a combined reinforcement, the minimum distance between centers of any two of these openings should preferably be at least 1½ times their average diameter, and the area of reinforcement between them shall be at least equal to 50% of the total required for these two openings.
(D.2.6) Rings, Pads, and Saddles. Reinforcement provided in the form of rings, pads, or saddles shall not be appreciably narrower at the side than at the crotch.
A vent hole shall be provided at the ring, pad, or saddle to provide venting during welding and heat treatment. Refer to para. 127.4.8(E).
Rings, pads, or saddles may be made in more than one piece, provided the joints between pieces have full thickness welds, and each piece is provided with a vent hole.
(D.2.7) Other Designs. The adequacy of designs to which the reinforcement requirements of para. 104.3 cannot be applied shall be proven by burst or proof tests on scale models or on full size structures, or by calculations previously substantiated by successful service of similar design
(E) Branch Connections Subject to External Pressure Requiring Reinforcement. The reinforcement area in square inches (square millimeters) required for branch connections subject to external pressure shall be
0.5tmhd1 (2 - sin a)
where tmh is the required header wall thickness determined for straight pipe under external pressure, using procedures outlined in UG-28, UG-29, UG-30, and UG-31 of Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code.
Procedures established heretofore for connections subject to internal pressure shall apply for connections subject to external pressure provided that Doh, Dob, and tr are reduced to compensate for external corrosion, if required by design conditions.
(F) Branch Connections Subject to External Forces and Moments. The requirements of the preceding paragraphs are intended to assure safe performance of a branch connection subjected only to pressure. However, when external forces and moments are applied to a branch connection by thermal expansion and contraction, by dead weight of piping, valves, and fittings, covering and contents, or by earth settlement, the branch connection shall be analyzed considering the stress intensification factors as specified in Appendix D. Use of ribs, gussets, and clamps designed in accordance with para. 104.3.4 is permissible to stiffen the branch connection, but their areas cannot be counted as contributing to the required reinforcement area of the branch connection.
(G) Extruded Outlets Integrally Reinforced
(G.1) The following definitions, modifications, notations, and requirements are specifically applicable to extruded outlets. The designer shall make proper wall thickness allowances in order that the required minimum reinforcement is assured over the design life of the system.
(G.2) Definition. An extruded outlet header is defined as a header in which the extruded lip at the outlet has an altitude above the surface of the run which is equal to or greater than the radius of curvature of the external contoured portion of the outlet; i.e., ho = r
o. See nomenclature and Fig. 104.3.1(G).
(G.3) These rules apply only to cases where the axis of the outlet intersects and is perpendicular to the axis of the run. These rules do not apply to any nozzle in which additional nonintegral material is applied in the form of rings, pads, or saddles.
(G.4) The notation used herein is illustrated in Fig. 104.3.1(G). All dimensions are in inches (millimeters).
D = outside diameter of run
d = outside diameter of branch pipe
db = corroded internal diameter of branch pipe
dc = corroded internal diameter of extruded outlet measured at the level of the outside surface of the run
dr = corroded internal diameter of run
ho = height of the extruded lip. This must be equal to or greater than ro, except as shown in (G.4.2) below.
L8 = altitude of reinforcement zone
