Abstract:
There is currently a need for large diameter flanges for the supply of water in South Africa. These large
diameter pipe flanges are required to accommodate pipes with nominal bores of up to 4 m and should
successfully withstand internal pressures of up to 8 MPa. No current relevant standard / code contains
prescribed design values for flanges which either operate at such high pressures or have such large
diameters. Due to this an alternative method of design, by means of non-linear finite element modelling,
is proposed. Three types of integral flange designs are considered, namely: flat face, raised face, and
a modified raised face with an O-ring groove. The effects of creep-relaxation, flange rotation, and the
bolting sequence are considered.
For each of these designs a finite element model was created and compared to a small scale experiment
which included strain and contact pressure measurements. The proposed non-linear finite element
models were capable of accurately predicting the strains in the flanges as well as the contact pressures
between the faces of the flange and the surfaces of the packing material. Finally, a comparison between
the ASME design method and the proposed non-linear finite element modelling design method was
done for the large diameter flanges. It was found that the ASME design code did not have the ability to
accurately predict the stresses in the flanges. It was also found that by using the maximum equivalent
Von Mises stress as failure criteria for the flanges and fasteners, and contact pressure for the sealing
ability, circular bolted flange connections which are lighter, safer, and leak tight could be designed by
means of the proposed non-linear finite element models.
