Page 68 - Pipelines and Risers

BucklingKoIlapse of Deepwater MetaIIic Pipes 41

The cross sectional deformations just before failure of pipes subjected to single loads are
shown in Figure 3.1.

Pure bending Pure pressure Pure longitudinal force

Figure 3.1 Cross sectional deformation of pipes Subjected to single loads.

3.2.2 External Pressure
Initial elliptical and corrosion defects are the two major types of imperfections influencing
collapse capacity of pipes. In the following, the work by Timoshenko and Gere (1961) is
extended, by Bai and Hauch (1998), to account for the effect of corrosion defects.

The deviation of an initial elliptical form from a perfect circular form can be defined by a
radial deflection ‘wi’ that, for simplification purposes, is assumed given by the following
equation:
wi = w, 428) (3.1)

in which ‘w1’ is the maximum initial radial deviation from a circle and ‘8’ is the central angle
measured as shown in Figure 3.2.
w,
:

W,
I
Figure 3.2 Circular and Elliptic pipe section.