Design and size recommendations

The aim in designing the flange coupling is to optimize the number and size of the bolts for the flange coupling as well as the dimensions of the flanges. The number of bolts in a coupling should not be less than six.
The Supergrip bolt is designed for a maximum shear stress of 280 N/mm2 and a maximum axial stress of 350 N/mm2.


=nominal torque [Nm]
TD=design torque [Nm]
TS=torque transmitted by Supergrip bolts [Nm]
TT=torque transmitted by tie bolts [Nm]
n1=number of Supergrip bolts
n2=number of tie bolts
S=shock factor
K1=max shear force [N]
K2=tensioning force on the Supergrip bolts [N] (table)
K3=tensioning force on the tie bolts [N] (table)
a=flange material factor (diagram 1)
b1=factor for remaining prestress in Supergrip bolts = 0,7
b2=factor for remaining prestress in tie bolts = 0,8

Geometrical dimensions

E=pitch circle diameter [mm]
=nominal hole diameter Supergrip bolt [mm]
d2=nominal hole diameter Tie bolt [mm]
d3=shaft diameter [mm]
G=bolt thread [mm]
D1=outer diameter of the flange [mm]
DD=outer diameter of the hydraulic tensioner [mm]
B1=long threaded bolt end Supergrip bolt [mm]
B2=short threaded bolt end Supergrip bolt [mm]
B3=short threaded bolt end Tie bolt [mm]
Cmin=min thickness of both flanges together [mm]
DM=nut diameter [mm]
F=nut thickness [mm]
Rmin=min radius for use of standard tool design [mm]
H1=min space to operate tensioner [mm]

Design torque

The design torque is determined in accordance with

TD = TN S [Nm] .............(1)

The shock factor S can be selected from the table.

Number of Supergrip bolts

Start with assuming a bolt size, then determine the pitch circle diameter E as follows
E = d3 + DD + 10 [mm] .............(2)

Calculate max shear force per bolt for the selected bolt size
K1 = 280 (π d12)a/4 [N] .............(3)

The number of Supergrip bolts is then determined from
n1 = TD2000/(E(K1 + K2 b1 0,15)) .............(4)

If the number of Supergrip bolts is less than six, select a smaller bolt size and repeat the calculation.

Outer diameter of the flange

The outer diameter of the flange is determined from

D1 = E + 1,6 d1 .............(5)

Flange material factor a

Due to the contact stress in the flange when the coupling is in service, the flange material must be considered (diagram 2).

Combination system

In case the Supergrip combination system is used, for instance at retrofitting, the number of Supergrip bolts and tie bolts are selected as follows.

The design torque is determined in accordance with formula (1)

Select a Supergrip bolt size and determine the pitch circle diameter in accordance with formula (2). The number of tie bolts should be a multiple of the number of Supergrip bolts (1, 2, 3....).

Select a suitable number of Supergrip bolts n1 not less than three.

Calculate the torque transmitted by the Supergrip bolts

TS = n1 E (K1+ K2 b1 0,15)/2000 [Nm] .............(6)

Determine the torque needed to be transmitted by the tie bolts from

TT = TD - TS [Nm] .............(7)

The number of tie bolts n2 is then calculated from

n2 = TT 2000/(K3 b2 E 0,15) .............(8)

Material specification

Bolt shank, sleeve and nuts:
Grade SS 2541 equivalent toB.S. 817M40
DIN 34NiCrMo6
SAE 4337
Mechanical propertiesReL = 700 N/mm2
A5 = min 12%

Conversion table

1 N = 0,102 kp = 0,225 lb
1 Nm = 0,102 kpm = 0,738 lbf
1 MPa = 10,2 kp/cm2 = 145 lb/in2
1 N/mm2 = 0,102 kp/mm2 = 145 lb/in2
1 m = 39,37 in
1 mm = 0,03937 in
1 in = 25,4 mm
0 °C = 273,15 K = 32 °F
SKF logo