ASME Section VIII div 2 2010. ASME Boiler and Pressure Vessel Code. Alternative Rules

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2010 SECTION VIII, DIVISION 2

4-335

4.17 Design Rules for Clamped Connections

4.17.1 Scope

The rules in paragraph 4.17 apply specifically to the design of clamp connections for pressure vessels and

vessel parts. These rules shall not be used for the determination of thickness of supported or unsupported

tubesheets integral with a hub nor for the determination of thickness of covers. These rules provide only for

hydrostatic end loads, assembly, and gasket seating.

4.17.2 Design Considerations

4.17.2.1 The design of a clamp connection involves the selection of the gasket, bolting, hub, and clamp

geometry. Connection dimensions shall be such that the calculated stresses in the clamp and the hub do not

exceed the acceptability criteria of this paragraph.

4.17.2.2 In the design of a bolted flange connection, calculations shall be made for the following two

design conditions, and the most severe condition shall govern the design of the flanged joint.

a) Operating Conditions – The conditions required to resist the hydrostatic end force of the design pressure

and any applied external forces and moments tending to part the joint, and to maintain on the gasket or

joint-contact surface sufficient compression to assure a joint that meets the required tightness, all at the

design temperature.

b) Gasket Seating And Assembly Condition – The conditions existing when the gasket or joint-contact

surface is seated by applying an initial load with the bolts when assembling the joint, at atmospheric

temperature and pressure.

4.17.2.3 Calculations shall be performed using dimensions of the flange in the corroded condition and the

uncorroded condition, and the more severe case shall control.

4.17.2.4 It is recommended that either a pressure energized and/or low seating load gasket be used to

compensate for possible non-uniformity in the gasket seating force distribution. Hub faces shall be designed

such as to have metal-to-metal contact outside the gasket seal diameter. This may be provided by recessing

the hub faces or by use of a metal spacer (see Figure 4.17.1). The contact area shall be sufficient to prevent

yielding of either the hub face or spacer under both operating and assembly loads.

4.17.2.5 It is recognized that there are clamp designs that do not utilize wedging action during assembly

since clamping surfaces are parallel to the hub faces. Such designs are acceptable and shall satisfy the

bolting and corresponding clamp and hub requirements of a clamp connection designed for a total included

clamping angle of 10 degrees.

4.17.2.6 The design method used in this paragraph to calculate stresses, loads, and moments may also

be used for designing clamp connections of shapes differing from those shown in Figures 4.17.1 and 4.17.2,

and for clamps consisting of more than two circumferential segments. The design equations in this

paragraph may be modified when designing clamp connections of shapes differing from those shown in

Figures 4.17.1 and 4.17.2, provided that the basis for the modifications is in accordance with paragraph

1.1.1.2. The clamp connections designed in this manner shall be provided with a bolt retainer. The retainer

shall be designed to hold the clamps together independently in case of failure of one of the primary bolting

([see paragraph 4.8). Multiple bolting (two or more bolts per lug) is an acceptable alternative for meeting this

requirement. Clamp-hub friction shall not be considered as a retainer method.

4.17.3 Flange Materials

4.17.3.1 Materials used in the construction of clamp connections shall comply with the requirements given

in Part 3.

2010 SECTION VIII, DIVISION 2

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4.17.3.2 Hubs made from ferritic steel and designed in accordance with the rules herein shall be given a

normalizing or full-annealing heat treatment when the thickness of the hub neck section exceeds 76 mm (3

in.).

4.17.3.3 Cast steel hubs and clamps shall be examined and repaired, if required, in accordance with Part

4.17.3.4 Hubs and clamps shall not be machined from plate.

4.17.3.5 Bolts, studs, nuts and washers shall comply with Part 3. The minimum bolt diameter shall be 13

mm (0.5 in.).

4.17.4 Design Bolt Loads

4.17.4.1 During assembly of the clamp connection, the design bolt load

W is resolved into an effective

clamp preload

W , which is a function of the clamp-to-hub taper angle

and the friction angle

. An

appropriate friction angle shall be established by the manufacturer, based on test results for both assembly

and operating conditions

4.17.4.2 The procedure to determine the bolt loads for the operating, and gasket seating and assembly

conditions are shown below.

a) STEP 1 – Determine the design pressure and temperature of the flange joint.

b) STEP 2 – Select a gasket and determine the gasket factors

m and

from Table 4.16.1.

c) STEP 3 – Determine the width of the gasket, basic gasket seating width, the location of the gasket

reaction,

, based on the flange and gasket geometry and the information in Table 4.16.3.

1) When

6 (0.25 .)bmm in≤ , then

is the mean diameter of the gasket or joint contact face

2) When

6 (0.25 .)bmm in> , then

is the outside diameter of the gasket contact face minus

d) STEP 4 – Determine the flange forces for the bolt load calculation.

0.785HGP= (4.17.1)

H b GmP for non self energized gaskets

=−−

(4.17.2)

H bGy for non self energized gaskets

=−− (4.17.3)

0.0

H for self energized gaskets=− (4.17.4)

0.0

H for self energized gaskets=− (4.17.5)

Note that where a significant axial force is required to compress the gasket during assembly of a joint

containing a self-energizing gasket, the value of

H shall be taken as equal to that axial force.

e) STEP 5 – Determine the design bolt load for the operating condition.

()

[]

tan

WHH

=+ − (4.17.6)

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2010 SECTION VIII, DIVISION 2

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f) STEP 6 – Determine the minimum required total bolt load for gasket seating and assembly conditions.

[]

tan

=+ (4.17.7)

()

[]

tan

WHH

=+ + (4.17.8)

g) STEP 7 – Determine the design bolt load for the gasket seating and assembly condition.

()

mbbg

AAS

(4.17.9)

The parameter

A is the actual total cross sectional area of the bolts that is selected such that

AA≥ ,

where

max , ,

222

bo bg bg

SSS

⎡⎤

⎢⎥

⎣⎦

(4.17.10)

4.17.4.3 In Equation (4.17.6), credit for friction is allowed based on clamp connection geometry and

experience, but the bolt load shall not be less than that determined using a value of

()

− equal to 5°.

Friction is also considered in determining bolt loads by Equation (4.17.7) and Equation (4.17.8), but the

factor used shall not be less than 5°.

4.17.5 Flange and Clamp Design Procedure

The procedure to design a clamp connection is shown below.

a) STEP 1 – Determine the design pressure and temperature of the flange joint.

b) STEP 2 – Determine an initial flange and clamp geometry (see Figures 4.17.1 and 4.17.2).

c) STEP 3 – Determine the design bolt loads for operating condition,

W , and the gasket seating and

assembly condition,

W , from paragraph 4.17.4.2.

d) STEP 4 – Determine the flange forces,

, and

H from paragraph 4.17.4.2.d, and

0.785

HBP= (4.17.11)

[]

()

1.571

tan

HHH

φμ

=−+

(4.17.12)

HHH=− (4.17.13)

e) STEP 5 – Determine the flange moment for the operating condition.

oDGTFPR

MMMMMM=+++++ (4.17.14)

where

2010 SECTION VIII, DIVISION 2

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()

CBg

⎡⎤

−+

⎢⎥

⎣⎦

(4.17.15)

GGG

Hh= (4.17.16)

()

⎡⎤

=−

⎢⎥

⎣⎦

(4.17.17)

−

⎛⎞

⎜⎟

⎝⎠

(4.17.18)

PBT h

⎛⎞

=−

⎜⎟

⎝⎠

(4.17.19)

()

[

]

tan

1.571

MWhT

⎛⎞

−

=−+

⎜⎟

⎝⎠

(4.17.20)

()

(4.17.21)

()

122

Tg hg

Tg h g

(4.17.22)

[

]

tan

=− (4.17.23)

f) STEP 6 – Determine the flange moment for the gasket seating condition

()

[]

0.785

tan

WCG

φμ

−

(4.17.24)

g) STEP 7 – Determine the hub factors

()

3.305

1.818

0.5

FTh

gBg

⎡⎤

=+ − +

⎢⎥

⎣⎦

(4.17.25)

()

122

22 1

=+−+

gT g h

gh gT h (4.17.26)

()

122 12

122

Tg h g g g

Tg h g

(4.17.27)

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2010 SECTION VIII, DIVISION 2

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h) STEP 8 – Determine the reaction shear force at the hub neck for the operating condition.

1.818

FBg

= (4.17.28)

i) STEP 9 – Determine the reaction shear force at the hub neck for the gasket seating condition.

1.818

FBg

(4.17.29)

j) STEP 10 – Determine the clamp factors.

bc c

eB lX=−−−

(4.17.30)

()

0.5

⎛⎞

−−−

⎜⎟

⎝⎠

twgc

CCCl

(4.17.31)

123c

AAAA=++ (4.17.32)

34 3

ctc

CAX

⎛⎞

=+ + −

⎜⎟

⎝⎠

(4.17.33)

()

wtt

CCC=− (4.17.34)

1.571

C= (4.17.35)

()

3 wgc

ACCl=− (4.17.36)

k) STEP 11 – Determine the hub stress correction factor,

, based on

g ,

g , h , and

using the

equations in Table 4.16.5 and

l using the following equation.

0.5( )=− −

mc i

ll CC (4.17.37)

l) STEP 12 – Determine the flange and clamp stresses for the operating and gasket seating conditions

using the equations in Table 4.17.1.

m) STEP 13 – Check the flange stress acceptance criteria for the operating and gasket seating conditions

are shown in Table 4.17.2. If the stress criteria are satisfied, then the design is complete. If the stress

criteria are not satisfied, then re-proportion the flange dimensions and go to STEP 2.

2010 SECTION VIII, DIVISION 2

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4.17.6 Nomenclature

A outside diameter of the hub.

A cross-sectional area of the bolts based on the root diameter or the least diameter of the

unthreaded portion, if less.

A effective clamp cross sectional area.

A total minimum required cross-sectional area of the bolts.

A partial clamp area.

A partial clamp area

hub transition angle, maximum 45

°.

inside diameter of the hub.

radial distance from connection center line to the center of the bolts.

effective gasket contact width.

b basic gasket seating width.

C diameter of effective clamp-hub reaction circle.

C inside diameter of clamp.

C effective clamp gap determined at diameter C .

C effective clamp thickness subject to the following condition

Cr≥ .

C clamp width.

e radial distance from center of the bolts to the centroid of the clamp cross section

hub stress correction factor.

factor relating total rotational moment to the reaction moment at the hub neck

g thickness of hub neck at small end.

g thickness of hub neck at intersection with hub shoulder.

g height of hub shoulder.

g radial distance from the hub inside diameter

to the hub shoulder ring centroid.

G location of the gasket reaction.

taper hub length.

h radial distance from effective clamp-hub reaction circle to the circle on which

H acts.

h average thickness of hub shoulder

h axial distance from the hub face to the hub shoulder ring centroid

H total hydrostatic end force.

H hydrostatic end force on bore area.

H difference between total effective axial clamping preload and the sum of total hydrostatic end

force and total joint contact surface compression.

H total axial gasket seating requirements for makeup.

H total joint contact surface compression load.

H difference between total hydrostatic end force and hydrostatic end force on bore area.

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2010 SECTION VIII, DIVISION 2

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moment of inertia of clamp relative to neutral axis of entire section.

moment of inertia of hub shoulder relative to its neutral axis

L distance from W to the point where the clamp lug joins the clamp body.

L clamp lug height.

L clamp lug width.

l effective clamp lip length.

l effective clamp lip moment arm.

moment due to

H .

offset moment.

moment due to

H .

pressure moment.

radial clamp equilibriating moment.

moment due to

H .

flange design moment for the operating condition.

flange design moment for the gasket seating condition.

friction angle.

m gasket factor.

N outside diameter of hub neck.

m gasket factor.

P design pressure.

clamp shoulder angle, maximum 40

reaction shear force at the hub neck for the gasket seating condition.

Q reaction shear force at the hub neck for the design operating condition.

r clamp or hub cross section corner radius.

S allowable stress from Annex 3.A for the bolt evaluated at the gasket seating temperature.

S allowable stress from Annex 3.A 3 for the bolt evaluated at the design temperature.

S allowable stress from Annex 3.A for the clamp evaluated at the gasket seating temperature.

S allowable stress from Annex 3.A for the clamp evaluated at the design temperature.

S allowable stress from Annex 3.A for the hub evaluated at the gasket seating temperature.

S allowable stress from Annex 3.A for the hub evaluated at the design temperature.

hub longitudinal stress on outside at hub neck for the design gasket seating condition.

S hub longitudinal stress on outside at hub neck for the design operating condition.

S maximum Lame hoop stress at bore of hub for the design gasket seating condition.

S maximum Lame hoop stress at bore of hub for the design operating condition.

S maximum hub shear stress at shoulder for the design gasket seating condition.

S maximum hub shear stress at shoulder for the design operating condition.

S maximum radial hub shear stress in neck for the design gasket seating condition.

2010 SECTION VIII, DIVISION 2

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S maximum radial hub shear stress in neck for the design operating condition.

S clamp longitudinal stress at clamp body inner diameter for the design gasket

seatingcondition.

S clamp longitudinal stress at clamp body inner diameter for the design operating condition.

S clamp tangential stress at clamp body outer diameter for the design gasket seating condition.

S clamp tangential stress at clamp body outer diameter for the design operating condition.

maximum shear stress in clamp lips for the design gasket seating condition.

S maximum shear stress in clamp lips for the design operating condition.

S clamp lug bending stress for the design gasket seating condition.

S clamp lug bending stress for the design operating condition.

S effective bearing stress between clamp and hub for the design gasket seating condition.

S effective bearing stress between clamp and hub for the design operating condition.

thickness of hub shoulder.

W clamp connection design bolt load for the gasket seating and assembly condition.

W clamp connection design bolt load for the gasket seating condition.

W clamp connection design bolt load for the assembly condition.

W clamp connection design bolt load for the design condition.

clamp dimension to neutral axis.

y gasket seating stress.

clamp-hub taper angle.

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2010 SECTION VIII, DIVISION 2

4-343

4.17.7 Tables

Table 4.17.1 – Flange Stress Equations

Location Stress Equations

Operating Condition Gasket Seating/Assembly Conditions

Flange

()()

111 1

1.91

gBg g BgF

⎡⎤

⎢⎥

⎣⎦

⎛⎞

⎜⎟

−

⎝⎠

()()

0.75

2tan

TB g

+−

()

0.477

gB g

()

1.91

gBgF

⎡

⎤

⎢

⎥

⎢

⎥

⎣

⎦

0.0

()()

0.75

2tan

TB g

()

0.477

gB g

Clamp

()

(

)

2tan

CCC

φμ

⎡

⎤

⎢

⎥

−

⎣

⎦

(

)

eCX

⎡⎤

⋅−

⎢⎥

⎣⎦

()

1.5

tan

CCC

−−

()()

tan

ACC

−−

()

(

)

2tan

CCC

φμ

⎡⎤

⎢⎥

⎣⎦

()

eCX

⎡

⎤

⋅−

⎢

⎥

⎣

⎦

()

1.5

tan

CCC

−+

()()

tan

ACC

−+

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Table 4.17.2 – Flange Stress Acceptance Criteria

Location Stress Acceptance Criteria

Operating Condition Gasket Seating/Assembly Conditions

Flange

1.5

oho

SS≤

2oho

SS≤

0.8

oho

SS≤

0.8

oho

SS≤

1.5

≤

0.8

≤

0.8

≤

Clamp

1.5

oco

SS≤

1.5

oco

SS≤

0.8

oco

SS≤

8oco

SS≤

[

]

1.6 min ,

ohoco

SSS≤

1.5

≤

1.5

≤

0.8

≤

1.6 min ,

hg cg

SSS

⎡

⎤

≤

⎣

⎦

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