Bifurcation Buckling Versus Limit Load Instabilities of Elastic-Plastic Tubes Under Bending and External Pressure

Commonly used procedures for installing offshore pipelines can induce substantial bending to the line in the presence of external pressure. These combined loads can lead to catastrophic collapse of the structure. For typically used steels and higher diameter-to-thickness ratios (D/t), bending is limited by a bifurcation type of instability; for lower D/t values, the structures exhibit limit load types of instabilities. Similar distinctions can be made for bending in the presence of external pressure. Previous work (Corona and Kyriakides, 1988) addressed primarily the limit load types of instabilities. In this paper, this analysis is extended to include bifurcation instabilities. The predictions from the two types of analyses are critically compared to experimental results and recommendations about the regime of applicability of each are made.