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17 BIFURCATIONS, SPECIAL FITTINGS AND CONNECTIONS

17 BIFURCATIONS, SPECIAL FITTINGS AND CONNECTIONS

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71

AS 4041 — 1998

Expansion fittings should comply with the following:
(i)

The annulus between an internal sleeve and a bellows should be drained.

(ii)

An internal liner should be fitted.

(iii) For fluid types 1 and 2 multiply-bellows with interply-leak monitoring should be
considered.
(iv)

For fluid type 2 using slip or gland type fitting safeguards should be taken to
prevent accidental leakage.

3.18.2 Flexible hose assemblies The design of a flexible metal hose assembly shall
comply with Clause 3.1.2. The service conditions and geometry shall be within the
limitations recommended by the manufacturer.
NOTE: A flexible hose assembly may be used to provide flexibility in a piping system, to
isolate or control vibration, or to compensate for misalignment.

3.19

BRANCH CONNECTIONS AND OPENINGS

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3.19.1 Application This Clause (3.19) is applicable to the design
connections and openings subject to internal or external pressure where —

of

branch

(a)

the axes of the branch or the opening and the main pipe intersect; and

(b)

the smaller angle between the axes of the branch and the main pipe is not less
than —

(c)

(i)

for Class 1 piping . . . . . . . . . . . . . . . 60°, or 45° when agreed between the
parties concerned; or

(ii)

for Class 2 or Class 3 piping . . . . . . . 45°.

The rules in Clauses 3.19.7 to 3.19.9, inclusive, are minimum requirements, valid
only for branch connections in which (using notations of Figure 3.19.8.2) —
(i)

the run pipe diameter-to-thickness ratio (Doh/th) is less than 100 and branchto-run diameter ratio (Dob/Doh) is not greater than 1.0; and

(ii)

for run pipe with (Doh/th) > 100, the branch diameter Dob is less than one-half
the run diameter Doh.

Where the provisions of Items (a), (b) and (c) are not met, design pressure shall be
qualified as required by Clause 3.22.
Where the axes of the branch or openings and the main pipe do not intersect, or where the
angle between the axis is less than 60°, the design shall comply with Clauses 3.22 and
3.24, but the requirements of this Clause (3.19) may be used as a guide.
NOTE: Due to the difficulty involved in making a satisfactory welded joint at the intersection
of a main pipe and a branch pipe not at right angles, it is recommended that where practicable,
the required angle between the main pipe and the branch be obtained by making a straight
connection at right angles to the main pipe and joining a bent length of branch pipe, a bend, or
elbow to the straight connection.

3.19.2 Types of branch connections
the use of one of the following:

A branch shall be connected to the main pipe by

(a)

A flanged fitting such as a tee, cross, 45° lateral, true Y, or double branch elbow as
specified in a nominated Standard.

(b)

A welding fitting, being a factory-made wrought steel butt-welding fitting such as a
tee or a cross as specified in a nominated Standard, or a forged steel socket-welding
or threaded fitting such as a tee, a cross, coupling or half-coupling as specified in a
nominated Standard.

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AS 4041 — 1998

72

(c)

A reinforced fitting such as the typical integrally reinforced set-on or set-in branch
fittings shown in Appendix K.

(d)

Welding directly to the main pipe with or without added reinforcement as specified
in this Clause (3.19).

(e)

Socket-welding or threading to attach the branch pipe directly to the main pipe with
or without added reinforcement.

(f)

An integrally reinforced extruded outlet as specified in this Clause (3.19).

3.19.3 Shape of opening Where the shape of the opening is other than circular, the
maximum value for area to be compensated (A7 Figure 3.19.8.2) may not be on the
longitudinal plane of the pipe or header.
NOTE: For the calculation of A7 on a plane other than the longitudinal plane see AS 1210.

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3.19.4 Size of branches and openings No limit is specified for the size of a branch
and an opening, however, the size of the branch determines the need for additional
reinforcement. See Clause 3.19.7 for branches not requiring additional reinforcement and
Clause 3.19.8 for branches requiring additional reinforcement.
3.19.5 Location of unreinforced branch connections A branch connection should be
located so the distance from the outside diameter of the branch from any longitudinal
spiral or circumferential weld in the main pipe is not less than 4 times the nominal
thickness of the main pipe. If the weld cannot be avoided, Clause 3.5.1.3 of
AS 1210 — 1997 shall be complied with.
3.19.6 Material for branches and reinforcement Material for a branch pipe and the
reinforcement for a branch and its opening shall be compatible with the main pipe (see
Clause 3.19.8.5 for requirements for reinforcement in material of strength different to that
of the main pipe). It is recommended that in austenitic steel pipes at high temperatures,
only forged tees be used.
3.19.7

Branches or openings not requiring additional reinforcement

3.19.7.1 General Certain branches or openings, by virtue of the material, design and
method of manufacture of the branch or main pipe, have adequate pressure strength and
integral reinforcement and do not require additional reinforcement.
It may be assumed that a branch connection has adequate strength to withstand the
internal and external pressure without additional reinforcement where it complies with this
Clause (3.19.7).
3.19.7.2 Fitting A flanged fitting, welded fitting, 45° lateral, reducer, true Y, or double
branch elbow shall be used within the pressure-temperature rating specified in the
nominated Standard, provided that the nominal wall thickness of the fitting is not less
than that determined in accordance with Clause 3.14.2.

A1

3.19.7.3 Coupling A threaded or socket-welding coupling, or half-coupling, welded
directly to the pipe may be used, provided that the nominal size of the branch pipe is not
 larger than the smaller of —
(a)

DN 50; and

(b)

one quarter of the outside diameter of the main pipe.

Figures 3.19.7 (f) to (k) apply to Items (a) and (b) above.
The minimum wall thickness of a coupling in the reinforcement zone shall be not less
than that of the unthreaded branch pipe. The wall thickness of a threaded coupling shall
be measured from the root of the thread to the minimum outside diameter.
For set on fittings, the diameter of the hole in the main pipe shall be not greater than the
inside diameter of the coupling, and shall be concentric with the coupling.
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73

A1

AS 4041 — 1998

3.19.7.4 Reinforced fitting An integrally reinforced set-on or set-in branch connection
 fitting (typically MSS SP97 and see Appendix K), or a welding outlet fitting of proved
design, intended to be welded to the main pipe, shall comply with Clause 3.19.8.
The hole in the main pipe shall be concentric with the hole in the fitting.

A1

 3.19.7.5 Small bore branch The nominal size of a small bore branch pipe, socket or
 coupling welded directly to the main pipe shall be the smaller of —
(a)

DN 25; and

(b)

one quarter of the outside diameter of the main pipe.

A small bore branch should not be welded if the pipe is formed by cold expansion
exceeding 1.5 percent, of the outside diameter or is subjected to work hardening.
3.19.7.6 Threaded connection A threaded connection made by drilling and tapping the
main pipe and threading the branch pipe shall comply with the following:

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A1

 (a)

The nominal size of the branch pipe shall be the smaller of DN 25 or one quarter of
the outside diameter of the main pipe.

(b)

The length of thread in the main pipe shall be not less than that shown in
Table 3.19.7(A), and Figure 3.19.7.

(c)

The minimum diameter of any welded-on or integrally cast connecting boss used to
provide the required length of engagement for the branch pipe shall be not less than
that shown in Table 3.19.7(B), and Figure 3.19.7(c).

(d)

See Clause 3.24.3 for limitations on threaded connections.
TABLE

3.19.7(A)

THREAD LENGTH FOR THREADED CONNECTION
millimetres
Nominal size of branch, DN
Thread length (l t) min. (see Note)

10
8

15

20

25

32

40

50

12.5

12.5

16.0

18.5

18.5

18.5

NOTE: The thread lengths specified in this table are equal to the effective thread length specified in AS 1722.1.

TABLE

3.19.7(B)

DIAMETER OF WELDED-ON OR INTEGRALLY-CAST CONNECTION BOSS
millimetres
Nominal size of branch, DN

10

15

20

25

32

40

50

Diameter (Db) min.

35

40

45

55

65

70

85

3.19.7.7 Socket-welded connection A socket-welded connection made by drilling and
counter-drilling the main pipe and fillet welding the branch pipe shall comply with
Figure 3.19.7 and the following:
A1

 (a)

The maximum nominal size of the branch pipe shall be the smaller of DN 25 or one
quarter of the outside diameter of the main pipe.

(b)

The minimum diameter and minimum depth of the socket shall be in accordance
with Table 3.19.7(C).

(c)

The minimum thickness of the drilled portion in the main pipe after counter-drilling
shall be 1.5 mm (see Figure 3.19.7(b)).

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AS 4041 — 1998

74

Where necessary, a welded-on connecting boss of weld metal shall be used to provide the
minimum length of 1.5 mm. The diameter of a welded-on connecting boss shall be not
less than that shown in Table 3.19.7(B).
TABLE

3.19.7(C)

DIAMETER AND DEPTH OF SOCKET-WELDING CONNECTION
millimetres
Nominal size of branch, connection, DN

10

15

20

25

32

40

50

Diameter of socket (A) min.

17.5

22

27

34

43

50

62

5

5

7

7

7

7

8

Depth of socket (B) min.

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3.19.7.8

Gamma-ray boss and plug

A gamma-ray boss shall be —

(a)

of a diameter not less than that shown in Table 3.19.7(B);

(b)

located not more than 150 mm from the weld to be radiographed; and

(c)

perpendicular to the main pipe.

The material for a gamma-ray boss and plug shall comply with Table 3.19.7(D), or shall
be agreed between the parties concerned.
Figure 3.19.7.8 illustrates a typical gamma-ray boss and plug.
TABLE

3.19.7(D)

GAMMA-RAY BOSS AND PLUG
Boss and plug material —
bar or forging

Pipe material
Carbon steel or
carbon-manganese steel

Carbon steel or carbon-manganese steel

1Cr-½Mo steel

Carbon steel, or carbon-manganese steel or same
material as the pipe

1¼Cr-½Mo steel

Carbon steel, carbon-maganese steel, 1Cr-½Mo, or the
same material as the pipe

2¼Cr-1Mo steel

1Cr-½Mo, 1¼Cr-½Mo or the same material as the pipe

½Cr-½Mo-¼V steel

2¼Cr-Mo or the same material as the pipe

Materials not listed above

Same as pipe

3.19.8

Branch connections or openings requiring reinforcement

3.19.8.1 General Where there is inadequate inherent reinforcement in the components
of a branch connection (see Clause 3.19.7), reinforcement shall be provided by one or
more of the following means:
(a)

Thickening of the main pipe, or the branch, or both (refer Appendix L).

(b)

Adding a reinforcement pad.

(c)

Other means agreed between the parties concerned (see Clause 3.22).

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AS 4041 — 1998

This Clause (3.19.8) specifies one method of determining the required reinforcement and
Appendix L gives details of another. Other methods shall be used only if agreed between
the parties concerned.
The design shall include the appropriate allowances so that the required minimum
reinforcement is retained during the design life of the piping.
If flexibility analysis is to be carried out to Appendix R, the branch must satisfy
Appendix L.

A1

3.19.8.2 Notation Figure 3.19.8.2 illustrates the notation used in the
pressure-temperature design of a branch connection, but does not illustrate the design
 allowances required to compensate for mill tolerance.
The notation shall be as follows:

A1



b
=
Dob =

subscript referring to branch pipe
outside diameter of branch pipe, in millimetres

Doh =

outside diameter of main pipe or header, in millimetres

d1

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A1



=
d2

A1

A1

A1

=

=

[Dob − 2(tb − G b)]
sin α

for connections at angles between 45° and 90°

‘half width’ of reinforcing zone, in millimetres


the greater of d1 and (tb − G b) + (th − G h)
but not greater than Doh




d1 

2

h

=

subscript referring to main pipe or header

G

=

corrosion, erosion, and other design allowances (see Clause 3.13)

L

=

height of reinforcement zone outside of main pipe, in millimetres

=

2.5(tb − Gb) + tr or 2.5(th − Gh), whichever is less

t

=

actual (by measurement), or minimum wall thickness of pipe, permissible
in the pipe specification, in millimetres

α

=

angle between axes of branch and main pipe, in degrees

tm

=

required minimum wall thickness of pipe for pressure-temperature design
conditions as determined by use of Equation 3.14.1, in millimetres

th

=

wall thickness of main pipe or header, in millimetres

tr

=

thickness of attached reinforcing pad, in Figure 3.19.8.2(b); or height of
the largest 60° right triangle supported by the main and branch pipe
outside diameter projected surfaces and lying completely within the area of
integral reinforcement, in Figure 3.19.8.2(c), in millimetres.





inside diameter of branch for right-angle connections, in millimetres

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AS 4041 — 1998
76

FIGURE 3.19.7 (in part)

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TYPICAL SMALL BORE BRANCH CONNECTIONS

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77

FIGURE 3.19.7 (in part)

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AS 4041 — 1998

TYPICAL SMALL BORE BRANCH CONNECTIONS

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AS 4041 — 1998

78

NOTES:
1

Connections shown are suitable for all classes of pipe, except (g), (h), (j) and (k) which are Class 3.

2

Connections shown are applicable where the maximum branch nominal size is the smaller of DN50 or
one quarter of the main outside diameter.

3

The minimum throat thickness of the weld in (g), (h), (j) and (k) welds shall be not less than the wall
thickness of the boss or the pipe, whichever is the thinner.

4

The toe angle on fillet F on the thinner of the branch and the main pipe is 45° maximum for Class 1
and Class 2 piping.

FIGURE 3.19.7 (in part)
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TYPICAL SMALL BORE BRANCH CONNECTIONS
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AS 4041 — 1998

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NOTES:
1

Both plug and boss shall be marked on top with a blunt stamp to identify the material: MS for carbon
steel, CML for 1Cr-½Mo steel.

2

Welding shall comply with this Standard.

3

Boss and plug welds shall blend into the parent metal and crack sensitive steels (2¼Cr-½Mo over
20 mm thick, ½Cr-½Mo-¼V, 5Cr-1Mo, 9Cr-1Mo and 12Cr-1Mo-V) shall be crack detected by
magnetic particle examination.

4

Postweld heat treatment which may be required on the weld between the boss and the pipe shall be
carried out in the workshop and not on site unless otherwise agreed.

5

After the main joint has been radiographed, the plug in Figure (a), shall be seal-welded to the boss
using a qualified welding procedure which, generally, does not require postweld heat treatment.

6

Both the boss and the plug shall be machined from bars or forgings. The material shall be as specified
in Table 3.19.7(D) and examined ultrasonically for freedom from laminar inclusions.

FIGURE 3.19.7.8

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GAMMA-RAY BOSS AND PLUG

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A1

NOTES:
1 Reinforcing saddles are to be used only on 90° branches.
2 When a ring or pad is added as reinforcement (see Figure 3.19.8.2(b)), the value of reinforcing area may be
taken in the same manner in which excess material in the main pipe is considered, provided a full
penetration weld is used between the branch, main pipe, and ring or pad.
3 The ratio of the width to thickness of a ring and a pad shall be as close to 4:1 as the available horizontal
space allows within the limits of the reinforcing zone along the main pipe and the outside diameter of the
branch allows, but the ratio shall be not less than 1:1.

FIGURE 3.19.8.2 (in part)

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REINFORCEMENT OF BRANCH CONNECTIONS

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81

AS 4041 — 1998

NOTE: For Items a, b and c the notations do not illustrate allowances for corrosion and erosion (see
Clause 3.19.8.2) and under-thickness tolerance.

FIGURE 3.19.8.2 (in part)

REINFORCEMENT OF BRANCH CONNECTIONS

3.19.8.3 Weld joint factor Where the main pipe contains a longitudinal or spiral weld
and the branch does not intersect the weld, the value of the weld joint factor (e) may be
taken to be unity for the purpose of the calculation of reinforcement, or the design
strength value of seamless pipe of comparable grade may be used to determine the value
of pressure design wall thickness.
Where the branch intersects a longitudinal or spiral weld in the main pipe, or if the branch
contains a longitudinal or spiral weld, the weld joint factor (e) for either or both shall be
included in calculations.
Where both the branch and the main pipe contain a longitudinal or spiral weld, the two
welds shall be staggered and the separation distance between the toes of the weld shall be
not less than four times the pipe thickness.
3.19.8.4 Required reinforcement area
determined as follows:
(a)
A1

The required reinforcement area shall be

Internal pressure The required reinforcement area for a branch connection under
internal pressure shall be the quantity —



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A7 = (tmh − G h)d1 (2 − sin α)

. . . 3.19.8.4(1)

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