ASME Section VIII div 2 2010. ASME Boiler and Pressure Vessel Code. Alternative Rules
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2010 SECTION VIII, DIVISION 2
4-125
na
RS
na nb
R
L L for nozzle A
RR
⎛⎞
=
⎜⎟
+
⎝⎠
(4.5.127)
nb
RS
na nb
R
L L for nozzle B
RR
⎛⎞
=
⎜⎟
+
⎝⎠
(4.5.128)
b) For three openings with overlapping limits of reinforcement (see Figure 4.5.12):
12
min ,
na na
RS S
na nb na nc
RR
L L L for nozzle A
RR RR
⎡⎤
⎛⎞⎛⎞
=
⎢⎥
⎜⎟⎜⎟
++
⎢⎥
⎝⎠⎝⎠
⎣⎦
(4.5.129)
13
min ,
nb nb
RS S
na nb nb nc
RR
L L L for nozzle B
RR RR
⎡⎤
⎛⎞⎛⎞
=
⎢⎥
⎜⎟⎜⎟
++
⎢⎥
⎝⎠⎝⎠
⎣⎦
(4.5.130)
23
min ,
nc nc
RS S
na nc nb nc
RR
L L L for nozzle C
RR RR
⎡⎤
⎛⎞⎛⎞
=
⎢⎥
⎜⎟⎜⎟
++
⎢⎥
⎝⎠⎝⎠
⎣⎦
(4.5.131)
c) For more than three openings with overlapping limits of reinforcement, repeat the above procedure for
each pair of adjacent nozzles.
4.5.14 Strength of Nozzle Attachment Welds
4.5.14.1 The strength of nozzle attachment welds shall be sufficient to resist the discontinuity force
imposed by pressure for nozzles attached to a cylindrical, conical, or spherical shell or formed head as
determined in paragraph 4.5.14.2. Nozzles attached to flat heads shall have their strength of attachment
welds evaluated as determined in paragraph 4.5.14.3. The effects of external forces and moments from
supplemental loads shall be considered.
4.5.14.2 The procedure to evaluate attachment welds of nozzles in a cylindrical, conical, or spherical shell
or formed head subject to pressure loading is shown below.
a) STEP 1 – Determine the discontinuity force factor
1) For nozzles abutting the vessel wall:
1.0
y
k = (4.5.132)
2) For nozzles inserted through the vessel wall:
nc n
y
nc
R
t
k
R
+
=
(4.5.133)
b) STEP 2 – Calculate Weld Length Resisting Discontinuity Force
1) Weld length of nozzle to shell weld
()
2
nn
L R t for radial nozzles
τ
π
=+ (4.5.134)
2010 SECTION VIII, DIVISION 2
4-126
()()
22
22
nc n n n
Rt Rt
L for nonradial nozzles
τ
π
+++
=
(4.5.135)
2) Weld length of pad to shell weld
()
2
pnn
L R t W for radial nozzles
τ
π
=++ (4.5.136)
()()
22
22
nc n n n
p
RtW RtW
L for nonradial nozzles
τ
π
++ + ++
=
(4.5.137)
c) STEP 3 – Compute the weld throat dimensions, as applicable.
41 41
0.7071
T
LL= (4.5.138)
42 42
0.7071
T
LL= (4.5.139)
43 43
0.7071
T
LL= (4.5.140)
d) STEP 4 – Determine if the weld sizes are acceptable.
1) If the nozzle is integrally reinforced, and the computed shear stress in the weld given by Equation
(4.5.141) satisfies Equation (4.5.142), then the design is complete. If the shear stress in the weld
does not satisfy Equation (4.5.142), increase the weld size and return to STEP 3. For nozzles on
heads,
2
A and
3
A are to be calculated using 1.0
=
p
F , when computing
welds
f
using Equation
(4.5.143).
()
41 1 43
0.49 0.6 0.49
τ
τ
=
++
welds
Tw T
f
LL t L
(4.5.141)
S
τ
≤ (4.5.142)
where,
()
23
min ,1.5
⎡⎤
=+
⎣⎦
welds Y y n
f
fk S A A (4.5.143)
2) If the nozzle is pad reinforced, and the computed shear stresses in the welds given by Equations
(4.5.144) through (4.5.146) satisfy Equation (4.5.147), then the design is complete. If the shear
stress in the weld does not satisfy Equation (4.5.147), increase the weld size and return to STEP 3.
()
1
143
0.6 0.49
ws
wT
f
Lt L
τ
τ
=
+
(4.5.144)
()
2
241
0.6 0.49
wp
wT
f
Lt L
τ
τ
=
+
(4.5.145)
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2010 SECTION VIII, DIVISION 2
4-127
()
3
42
0.49
wp
pT
f
LL
τ
τ
= (4.5.146)
[
]
123
max , , S
τττ
≤ (4.5.147)
where,
⋅
=
⋅+
welds y
ws
ep
f
kt S
f
tS tS
(4.5.148)
=
⋅+
welds y e p
wp
ep
f
ktS
f
tS tS
(4.5.149)
3) If the nozzle is pad reinforced, and the computed shear stress in the nozzle wall given by Equation
(4.5.150) satisfies Equation (4.5.151), then the design is complete. If the shear stress in the nozzle
wall does not satisfy Equation (4.5.151), increase the nozzle thickness in accordance with
paragraph 4.5.4.
1.4
τ
⎛⎞
−
⎜⎟
⎝⎠
=
n
Le
n
n
n
PR
Pt
t
t
(4.5.150)
1.5
τ
≤
nn
S (4.5.151)
4.5.14.3 The procedure to evaluate attachment welds of a nozzle in a flat head subject to pressure loading
is shown below.
a) STEP 1 – Compute the weld throat dimensions, as applicable.
41 41
0.7071
T
LL= (4.5.152)
42 42
0.7071
T
LL= (4.5.153)
43 43
0.7071
T
LL= (4.5.154)
b) STEP 2 – Determine if the weld sizes are acceptable.
1) If the nozzle is integrally reinforced and inserted through the flat head, and the computed shear
stress in the welds given by Equations (4.5.155) and (4.5.156) satisfy Equation (4.5.157), then the
design is complete. If the shear stress in the welds does not satisfy Equation (4.5.157), increase
the weld size and return to STEP 1.
1
143
0.6 0.49
τ
=
+
s
x
T
V
tL
(4.5.155)
2
241
0.6 0.49
τ
=
+
s
x
T
V
tL
(4.5.156)
2010 SECTION VIII, DIVISION 2
4-128
[
]
12
max , S
ττ
≤ (4.5.157)
where
4
3
0.3
=
rf
s
St
V
t
(4.5.158)
[
]
11
min , 0.5=
xw
ttt (4.5.159)
()
21
min max 0.5 , 0 , 0.5
⎡⎤
=−⎡⎤
⎣⎦
⎣⎦
xw
tttt (4.5.160)
2) If the nozzle is pad reinforced and inserted through the flat head, and the computed shear stress in
the welds given by Equations (4.5.161) through (4.5.163) satisfy Equation (4.5.164), then the design
is
complete. If the shear stress in the welds does not satisfy Equation (4.5.164), increase the weld
size and return to STEP 1.
1
143
0.6 0.49
τ
=
+
s
wT
V
tL
(4.5.161)
2
241
0.6 0.49
τ
=
+
s
wT
V
tL
(4.5.162)
()
3
42
0.49 ( )
τ
+
=
++
snn
Tn n
VR t
LRtW
(4.5.163)
[
]
123
max , , S
τττ
≤ (4.5.164)
The parameter
s
V is given by Equation (4.5.158).
3) If the nozzle is integrally reinforced and abutting the flat head, and the computed shear stress in the
weld given by Equation (4.5.165) satisfies Equation (4.5.166), then the design is complete. If the
shear stress in the weld does not satisfy Equation (4.5.166), increase the weld size and return to
STEP 1.
()
141
2
0.6 0.49
o
wT
M
tt L
τ
=
+
(4.5.165)
S
τ
≤ (4.5.166)
4.5.15 Local Stresses in Nozzles in Shells and Formed Heads from External Loads
Localized stresses at nozzle locations in shells and formed heads shall be evaluated using one of the method
shown below. For each method, the acceptance criteria shall be in accordance with Part 5.
a) Nozzles in cylindrical shells – stress calculations shall be in accordance with WRC 107 or WRC 297.
b) Nozzles in formed heads – stress calculations shall be in accordance with WRC 107.
c) For all configurations, and as an alternative to paragraph 4.5.15.a and paragraph 4.5.15.b, the stress
calculations may be performed using a numerical analysis such as the finite element method.
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2010 SECTION VIII, DIVISION 2
4-129
4.5.16 Inspection Openings
4.5.16.1 All pressure vessels for use with compressed air and those subject to internal corrosion or having
parts subject to erosion or mechanical abrasion (see paragraph 4.1.4), except as permitted otherwise in this
paragraph, shall be provided with a suitable manhole, handhole, or other inspection opening(s) for
examination and cleaning. Compressed air as used in this paragraph is not intended to include air which has
had moisture removed to provide an atmospheric dew point of -46°C (-50°F) or less.
4.5.16.2 Inspection openings maybe omitted in the shell side of fixed tubesheet heat exchangers. When
inspection openings are not provided, the Manufacturer's Data Report shall include one of the following
notations under remarks:
a) “Paragraph 4.5.16.2” when inspection openings are omitted in fixed tubesheet heat exchangers;
b) “Paragraph 4.5.16.3”, “Paragraph 4.5.16.4”, “Paragraph 4.5.16.5” when provision for inspection is made
in accordance with one of these paragraphs;
c) The statement "for noncorrosive service.”
4.5.16.3 Vessels over 300 mm (12 in.) inside diameter under air pressure which also contain, as an
inherent requirement of their operation, other substances which will prevent corrosion need not have
openings for inspection only, provided the vessel contains suitable openings through which inspection can be
made conveniently, and provided such openings are equivalent in size and number to the requirements for
inspection openings in paragraph 4.5.16.6.
4.5.16.4 For vessels 300 mm (12 in.) or less in inside diameter, openings for inspection only may be
omitted if there are at least two removable pipe connections not less than DN 20 (NPS ¾).
4.5.16.5 Vessels less than 400 mm (16 in.) and over 300 mm (12 in.) inside diameter shall have at least
two handholes or two threaded pipe plug inspection openings of not less than DN 40 (NPS 1-1/2) except as
permitted by the following: when vessels less than 400 mm (16 in.) and over 300 mm (12 in.) inside diameter
are to be installed so that inspection cannot be made without removing the vessel from the assembly,
openings for inspection only may be omitted provided there are at least two removable pipe connections of
not less than DN 40 (NPS 1-1/2).
4.5.16.6 Vessels that require access or inspection openings shall be equipped as follows:
a) All vessels less than 450 mm (18 in.) and over 300 mm (12 in.) inside diameter shall have at least two
handholes or two plugged, threaded inspection openings of not less than DN 40 (NPS 1-1/2);
b) All vessels 450 mm (18 in.) to 900 mm (36 in.), inclusive, inside diameter shall have a manhole or at
least two handholes or two plugged, threaded inspection openings of not less than DN 50 (NPS 2);
c) All vessels over 900 mm (36 in.) inside diameter shall have a manhole, except that those whose shape
or use makes one impracticable shall have at least two handholes 100 mm x 150 mm (4 in. x 6 in.) or
two equal openings of equivalent area;
d) When handholes or pipe plug openings are permitted for inspection openings in place of a manhole, one
handhole or one pipe plug opening shall be in each head or in the shell near each head service;
e) Openings with removable heads or cover plates intended for other purposes may be used in place of the
required inspection openings provided they are equal at least to the size of the required inspection
openings;
f) A single opening with removable head or cover plate may be used in place of all the smaller inspection
openings provided it is of such size and location as to afford at least an equal view of the interior;
g) Flanged and/or threaded connections from which piping, instruments, or similar attachments can be
removed may be used in place of the required inspection openings provided that:
1) The connections are at least equal to the size of the required openings; and
2010 SECTION VIII, DIVISION 2
4-130
2) The connections are sized and located to afford at least an equal view of the interior as the required
inspection openings.
4.5.16.7 When inspection or access openings are required, they shall comply at least with the following
requirements.
a) An elliptical or obround manhole shall be not less than 300 mm x 400 mm (12 in. x 16 in.). A circular
manhole shall be not less than 400 mm (16 in.) inside diameter.
b) A handhole opening shall be not less than 50 mm x 75 mm (2 in. x 3 in.), but should be as large as is
consistent with the size of the vessel and the location of the opening.
4.5.16.8 All access and inspection openings in a shell or unstayed head shall be designed in accordance
with the rules of this Part for openings.
4.5.16.9 When a threaded opening is to be used for inspection or cleaning purposes, the closing plug or
cap shall be of a material suitable for the pressure and no material shall be used at a temperature exceeding
the maximum temperature allowed in Part 3 for that material. The thread shall be a standard taper pipe
thread except that a straight thread of at least equal strength maybe used if other sealing means to prevent
leakage are provided.
4.5.16.10 Manholes of the type in which the internal pressure forces the cover plate against a flat gasket
shall have a minimum gasket bearing width of 17 mm (0.6875 in.).
4.5.17 Reinforcement of Openings Subject to Compressive Stress
4.5.17.1 The reinforcement for openings in cylindrical and conical vessels subject to compressive stress
that do not exceed 25% of the cylinder diameter or 80% of the ring spacing into which the opening is placed
may be designed in accordance with the following rules. Openings in cylindrical and conical vessels that
exceed these limitations shall be designed in accordance with Part 5.
4.5.17.2 Reinforcement for nozzle openings in cylindrical and conical vessels designed for external
pressure alone shall be in accordance with the requirements of paragraph 4.5.5 through paragraph 4.5.9, as
applicable. The required thickness shall be determined in accordance with paragraph 4.5.4.
4.5.17.3 For cylindrical and conical vessels designed for axial compression (which includes axial load
and/or bending moment) without external pressure, the reinforcement of openings shall be in accordance with
the following:
00.4
r
AfordRt=≤ (4.5.167)
()
2
0.5 0.4 0.22
291
rr n
Rt
A dt for d Rt and
γ
⎛⎞
=>≤+
⎜⎟
⎝⎠
(4.5.168)
()
2
0.4 0.22
291
rr n
Rt
A dt for d Rt and
γ
⎛⎞
=>>+
⎜⎟
⎝⎠
(4.5.169)
where,
2
n
d
R
t
γ
⎛⎞
=
⎜⎟
⎝⎠
(4.5.170)
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2010 SECTION VIII, DIVISION 2
4-131
4.5.17.4 The reinforcement shall be placed within a distance of
0.75
R
t from the edge of the opening.
Reinforcement available from the nozzle neck shall be limited to a thickness not exceeding the shell plate
thickness at the nozzle attachment, and be placed within a limit measured normal to the outside surface of
the vessel shell of
()
0.5 2
n
dt
, but not exceeding 2.5
n
t .
4.5.17.5 For cylindrical and conical vessels designed for axial compression in combination with external
pressure, the reinforcement shall be the larger of that required for external pressure alone, paragraph
4.5.17.2, or axial compression alone, paragraph 4.5.17.3. Required reinforcement shall be placed within the
limits described in paragraph 4.5.17.4.
4.5.18 Nomenclature
1
A area contributed by the vessel wall.
2
A area contributed by the nozzle outside the vessel wall.
3
A area contributed by the nozzle inside the vessel wall.
41
A area contributed by the outside nozzle fillet weld.
42
A area contributed by the pad to vessel fillet weld.
43
A area contributed by the inside nozzle fillet weld.
5
A area contributed by the reinforcing pad.
P
A area resisting pressure, used to determine the nozzle opening discontinuity force.
r
A area of reinforcement required.
T
A total area within the assumed limits of reinforcement.
α
one-half of the apex angle of a conical shell.
i
D inside diameter of a shell or head.
D
D distance from a major structural discontinuity to the nozzle center line.
R
D distance from the head center line to the nozzle center line.
T
D distance from the head tangent line to the nozzle center line..
X
D distance from the cylinder center line to the nozzle center line.
d
inside diameter of the opening.
s
t
d nominal diameter of the stud.
E
weld joint factor (see paragraph 4.2); 1.0E
=
if the nozzle does not intersect a weld seam.
s
t
E engagement length of a stud.
p
F
nozzle attachment factor.
ha
F minimum value of the allowable compressive stress of the shell and nozzle material from
paragraph 4.4, evaluated at the design temperature.
N
f
force from internal pressure in the nozzle outside of the vessel.
rn
f
nozzle material factor.
rp
f
pad material factor.
S
f
force from internal pressure in the shell.
y
f
discontinuity force from pressure.
2010 SECTION VIII, DIVISION 2
4-132
Y
f
discontinuity force from internal pressure.
ws
f
discontinuity force carried by welds
1w
t and
43
L .
wn
f
discontinuity force carried by welds
41
L and
2w
t and weld
42
L .
p
F nozzle attachment factor.
h height of the ellipsoidal head measured to the inside surface.
y
k discontinuity force factor that adjusts the discontinuity force to the nozzle outer diameter.
41
L weld leg length of the outside nozzle fillet weld.
42
L weld leg length of the pad to vessel fillet weld.
43
L weld leg length of the inside nozzle fillet weld.
L
inside crown radius of a torispherical head.
H
L effective length of nozzle wall outside the vessel.
I
L effective length of nozzle wall inside the vessel.
41T
L throat dimension of the outside nozzle fillet weld.
42T
L throat dimension for the pad to vessel fillet weld.
43T
L throat dimension for inside nozzle fillet weld.
R
L effective length of the vessel wall.
1pr
L nozzle projection from the outside of the vessel wall.
2pr
L nozzle projection from the inside of the vessel wall.
3pr
L length of variable thickness,
n
t , from the outside of the vessel wall.
L
τ
weld length of the nozzle to shell weld.
p
L
τ
weld length of the pad to shell weld.
P internal or external design pressure.
max
P nozzle maximum allowable pressure.
L
P maximum local primary membrane stress at the nozzle intersection.
R
vessel inside radius.
m
R
vessel mean radius.
eff
R
effective pressure radius.
n
R
nozzle inside radius.
nc
R
radius of the nozzle opening in the vessel along the long chord, for radial nozzles
nc n
R
R
=
nm
R
nozzle mean radius.
x
n
R
nozzle radius for force calculation.
x
s
R
shell radius for force calculation.
S allowable stress from Annex 3.A for the vessel at the design temperature.
n
S allowable stress from Annex 3.A for the nozzle at the design temperature.
p
S allowable stress from Annex 3.A for the pad at the design temperature.
s
t
S allowable stress from Annex 3.A of the stud material at the design temperature.
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2010 SECTION VIII, DIVISION 2
4-133
tp
S allowable stress from Annex 3.A of the tapped material at the design temperature.
avg
σ
average primary membrane stress.
circ
σ
general primary membrane stress.
θ
angle between the nozzle center line and the vessel center line.
t nominal thickness of the vessel wall.
e
t thickness of the reinforcing pad.
eff
t effective thickness used in the calculation of pressure stress near the nozzle opening.
n
t nominal thickness of the nozzle wall.
2n
t nominal wall thickness of the thinner portion of a variable thickness nozzle.
r
t thickness of shell required for axial compression loads without external pressure.
rf
t minimum required flat head thickness, exclusive of corrosion allowance, as required by
paragraph 4.6.
1w
t nozzle to shell groove weld depth.
2w
t nozzle to reinforcing pad groove weld depth.
τ
average “effective” shear stress in welds due to pressure (includes joint efficiency).
s
V shear load.
W width of the reinforcing pad.
o
X
distance from the nozzle outside diameter to the head center.
2010 SECTION VIII, DIVISION 2
4-134
4.5.19 Tables
Table 4.5.1 – Minimum Number of Pipe Threads for Connections
Size Of Pipe Threads Engaged Minimum Plate Thickness Required
DIN 15, 20
(NPS 0.5, 0.75 in.)
6 11 mm (0.43 in.)
DIN 25, 32, 40
(NPS 1.0, 1.25, 1.5 in.)
7 16 mm (0.61 in.)
DIN 50
(NPS 2 in.)
8 18 mm (0.70 in.)
Table 4.5.2 – Nozzle Minimum Thickness Requirements
Nominal Size Minimum Thickness
mm in
DN 6 (NPS 1/8) 1.51 0.060
DN 8 (NPS 1/4) 1.96 0.077
DN 10 (NPS 3/8) 2.02 0.088
DN 15 (NPS 1/2) 2.42 0.095
DN 20 (NPS 3/4) 2.51 0.099
DN 25 (NPS 1) 2.96 0.116
DN 32 (NPS 1 1/4) 3.12 0.123
DN 40 (NPS 1 1/2) 3.22 0.127
DN 50 (NPS 2) 3.42 0.135
DN 65 (NPS 2 1/2) 4.52 0.178
DN 80 (NPS 3) 4.80 0.189
DN 90 (NPS 3 1/2) 5.02 0.198
DN 100 (NPS 4) 5.27 0.207
DN 125 (NPS 5) 5.73 0.226
DN 150 (NPS 6) 6.22 0.245
DN 200 (NPS 8 ) 7.16 0.282
DN 250 (NPS 10) 8.11 0.319
≥ DN 300 (NPS 12)
8.34 0.328
Note: For nozzles having a specified outside diameter not equal to the outside diameter of an equivalent
standard DN (NPS) size, the DN (NPS) chosen from the table shall be one having an equivalent outside
diameter larger than the actual nozzle outside diameter.
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