To = corroded finished thickness of extruded outlet measured at a height equal to ro above the outside surface of the run
tb - A = actual thickness of branch wall, not including corrosion allowance
th - A = actual thickness of run wall, not including the corrosion allowance
tmb - A = required thickness of branch pipe according to wall thickness eq. (3) or (3A) in para. 104.1.2(A), but not including any thickness for corrosion
tmh - A = required thickness of the run according to eq. (3) or (3A) in para. 104.1.2(A), but not including any allowance for corrosion
r1 = half width of reinforcement zone (equal to dc)
ro = radius of curvature of external contoured portion of outlet measured in the plane containing the axes of the run and branch. This is subject to the following limitations:
(G.4.1) Minimum Radius. This dimension shall not be less than 0.05d except that on branch diameters larger than NPS 30, it need not exceed 1.50 in. (38 mm).
(G.4.2) Maximum Radius. For outlet pipe sizes 6 in. (150 mm) nominal and larger, this dimension shall not exceed 0.l0d + 0.50 in. (0.l0d + 12.7 mm). For outlet pipe sizes less than NPS 6, this dimension shall be not greater than 1.25 in. (32 mm).
(G.4.3) When the external contour contains more than one radius, the radius of any arc sector of approximately 45 deg shall meet the requirements of (G.4.1) and (G.4.2) above. When the external contour has a continuously varying radius, the radius of curvature at every point on the contour shall meet the requirements of (G.4.1) and (G.4.2) above.
(G.4.4) Machining other than grinding for weld cleanup shall not be employed in order to meet the above requirements.
(G.5) Required Area. The required area is defined as
A7 = K (tmh - A) dc
where K shall be taken as follows.
For d/D greater than 0.60,
K = 1.00
For d/D greater than 0.15 and not exceeding 0.60,
K = 0.6 + 2/3 d/D
For d/D equal to or less than 0.15,
K = 0.70
The design must meet criteria that the reinforcement area defined in (G.6) below is not less than the required area.
(G.6) Reinforcement Area. The reinforcement area shall be the sum of areas
A1 + A2 + A4
as defined below.
(G.6.l) Area Al is the area lying within the reinforcement zone resulting from any excess thickness available in the run wall.
A1 = dc(tn – tmh)
(G.6.2) Area A2 is the area lying within the reinforcement zone resulting from any excess thickness available in the branch pipe wall.
A2 = 2L8(tb – tmh)
(G.6.3) Area A4 is the area lying within the reinforcement zone resulting from excess thickness available in the extruded outlet lip.
A4 = 2ro [To – (tb – A)]
(G.7) 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 requirements shall be met. The two or more openings shall be reinforced in accordance with (G) with a combined reinforcement that has a strength equal to the combined strength of the reinforcement that would be required for 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.
(G.8) In addition to the above, the manufacturer shall be responsible for establishing and marking on the section containing extruded outlets, the design pressure and temperature. The manufacturer's name or trademarks shall be marked on the section.
104.3.3 Miters. Miter joints, and the terminology related thereto, are described in Appendix D. A widely spaced miter with
shall be considered to be equivalent to a girth buttwelded joint, and the rules of this paragraph do not apply. Miter joints, and fabricated pipe bends consisting of segments of straight pipe welded together, with q equal to or greater than this calculated value may be used within the limitations described below.
(A) Pressure shall be limited to 10 psi (70 kPa) under the following conditions:
(A.1) The assembly includes a miter weld with
q > 22.5 deg, or contains a segment which has a dimension
B < 6tn
(A.2) The thickness of each segment of the miter is not less than that determined in accordance with para. 104.1.
(A.3) The contained fluid is nonflammable, non-toxic, and incompressible, except for gaseous vents to atmosphere.
(A.4) The number of full pressure cycles is less than 7,000 during the expected lifetime of the piping system.
(A.5) Full penetration welds are used in joining miter segments.
(B) Pressure shall be limited to 100 psi (700 kPa) under the conditions defined in (A.2), (A.3), (A.4), and (A.5) above, in addition to the following:
(B.1) the angle q does not exceed 22.5 deg
(B.2) the assembly does not contain any segment which has a dimension
B < 6tn
(C) Miters to be used in other services or at design pressures above 100 psi (700 kPa) shall meet the requirements of para. 104.7.
(C.1) When justification under para. 104.7 is based on comparable service conditions, such conditions must be established as comparable with respect to cyclic as well as static loadings.
(C.2) When justification under para. 104.7 is based on an analysis, that analysis and substantiating tests shall consider the discontinuity stresses which exist at the juncture between segments; both for static (including brittle fracture) and cyclic internal pressure.
(C.3) The wall thickness, ts, of a segment of a miter shall not be less than specified in (C.3.1) or (C.3.2) below, depending on the spacing.
(C.3.1) For closely spaced miter bends (see Appendix D for definition)
(C.3.2) For widely spaced miters (see Appendix D for definition)
(The above equation requires an iterative or quadratic solution for ts.)
104.3.4 Attachments. External and internal attachments to piping shall be designed so as not to cause flattening of the pipe, excessive localized bending stresses, or harmful thermal gradients in the pipe wall. It is important that such attachments be designed to minimize stress concentrations in applications where the number of stress cycles, due either to pressure or thermal effect, is relatively large for the expected life of the equipment.
104.4 Closures
104.4.1 General. Closures for power piping systems shall meet the applicable requirements of this Code and shall comply with the requirements described in (A) or (B) below. Closures may be made
(A) by use of closure fittings, such as threaded or welded plugs, caps, or blind flanges, manufactured in accordance with standards listed in Table 126.1, and used within the specified pressure-temperature ratings, or
(B) in accordance with the rules contained in the ASME Boiler and Pressure Vessel Code, Section I, Power Boilers, PG-31, or Section VIII, Pressure Vessels, Division 1, UG-34 and UW-13, calculated from
tm = t + A
where
t = pressure design thickness, calculated for the given closure shape and direction of loading using appropriate equations and procedures in Section I or Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code.
The definition of A and the symbols used in determining t shall have the definitions shown herein, instead of those given in the ASME Boiler and Pressure Vessel Code.
Attachment of a welded flat permanent closure with only a single fillet weld is not permitted.
104.4.2 Openings in Closures. Openings in closures may be made by welding, extruding, or threading. Attachment to the closure shall be in accordance with the limitations provided for such connections in para. 104.3.1 for branch connections. If the size of the opening is greater than one-half of the inside diameter of the closure, the opening shall be designed as a reducer in accordance with para. 104.6.
Other openings in closures shall be reinforced in accordance with the requirements of reinforcement for a branch connection. The total cross-sectional area required for reinforcement in any plane passing through the center of the opening and normal to the surface of the closure shall not be less than the quantity of
d5t, where
d5 = diameter of the finished opening, in. (mm)
t = as defined in (B) above
121.8 Structural Attachments
121.8.1 Nonintegral Type
(A) Nonintegral attachments include clamps, slings, cradles, saddles, straps, and clevises.
(B) When clamps are used to support vertical lines, it is recommended that shear lugs be welded to the pipe to prevent slippage. The provisions of para. 12l.8.2(B) shall apply.
(C) In addition to the provision of (B) above, clamps to support vertical lines should be designed to support the total load on either arm in the event the load shifts due to pipe and/or hanger movement.
121.8.2 Integral Type
(A) Integral attachments include ears, shoes, lugs, cylindrical attachments, rings, and skirts which are fabricated so that the attachment is an integral part of the piping component. Integral attachments shall be used in conjunction with restraints or braces where multiaxial restraint in a single member is to be maintained. Consideration shall be given to the localized stresses induced into the piping component by the integral attachments. Where applicable, the conditions of para. 12l.8.1(C) are to apply.
(B) Integral lugs, plates, angle clips, etc., used as part of an assembly for the support or guiding of pipe may be welded directly to the pipe provided the materials are compatible for welding and the design is adequate for the temperature and load. The design of hanger lugs for attachment to piping for high temperature service shall be such as to provide for differential expansion between the pipe and the attached lug.
121.9 Loads and Supporting Structures
Considerations shall be given to the load carrying capacity of equipment and the supporting structure. This may necessitate closer spacing of hangers on lines with extremely high loads.
121.10 Requirements for Fabricating Pipe Supports
Pipe supports shall be fabricated in accordance with the requirements of para. 130.
PART 6
SYSTEMS
122 DESIGN REQUIREMENTS PERTAINING TO SPECIFIC PIPING SYSTEMS
Except as specifically stated otherwise in this Part 6, all provisions of the Code apply fully to the piping systems described herein.
122.1 Boiler External Piping; in Accordance With Para. 100.1.2(A) -Steam, Feedwater, Blowoff, and Drain Piping
122.1.1 General. The minimum pressure and temperature and other special requirements to be used in the design for steam, feedwater, blowoff, and drain piping from the boiler to the valve or valves required by para. 122.1 shall be as specified in the following paragraphs. Design requirements for desuperheater spray piping connected to desuperheaters located in the boiler proper and in main steam piping are provided in para. 122.4.
