Gasket contact stress variation
Gasket contact stress is the most important parameter
used to analyse the sealing capability of a gasketed
bolted flange joint. Gasket stress is noted at the inner
and outer sealing ring for target torque of 700 Nm
(Figs 3(a) to (d)) and 505 Nm (Fig. 3(e)). Along the outside
diameter of the sealing ring, the first two passes
show the same stress trend with average stresses of 26
and 50 MPa, respectively, for both the bolt up strategies.
Stress variation is obvious from the third pass
Q5 onwards. During the third pass a maximum stress of
120 and 170 MPa is observed along bolt 2 for ASME
and industrial bolt up strategies (Figs 3(a) and (b). For
the last pass, maximum stress noted is 172 MPa along
bolt 2 compared to 154 MPa along bolt 3 location.
Overall, gasket contact stress variation is observed to
be smooth for ASME bolt up strategy compared to
the industrial bolt up strategy and is concluded to be
beneficial from the sealing point of view.
At the inside diameter of the sealing ring, maximum
average gasket stress of 15 and 40 MPa is observed
for the first two passes for both the bolt up strategies
(Figs 3(c) and (d)). From the third pass onwards
Q6 an obvious stress variation is observed. An average
stress of 55 MPa is observed for the industrial bolt up
strategy compared to 105 MPa for the ASME bolt up
strategy. It is concluded because of the higher target
torque values for this pass. In addition, a large stress
variation is observed even for the ASME bolt up strategy.
However for the last CW pass, stress variation is
relatively smooth with a maximum stress of 153 MPa
along bolt 2. From Figs 3(c) and (d), it is observed
that the minimum required gasket stress of 68 MPa is
achieved with 4.5 per cent high average contact stress
and is attained for the ASME bolt up strategy compared
to the industrial bolt up strategy for the same target
torque of 700 Nm. When the same bolted flange joint
is subjected to 505 Nm target torque with the industrial
standard bolt up strategy, a maximum stress of
105 MPa is obtained in the vicinity of bolts 1, 2, and 3
but the contact stress tends to decrease and reaches
a minimum stress of 57 MPa in the vicinity of bolts 5,
6, and 7, which is below the required minimum gasket
stress (Fig. 3(e)). This concludes that the target torque
of 505 Nm is not sufficient to achieve the required gasket
sealing stress and may result in leakage; therefore,
it is not recommended for industrial applications.