TABLE OF CONTENTS Bending is a primary loading experienced by pipelines during installation and operation. For typical pipe D/t s and line grade steels, bending and the associated limit states are affected by the plastic characteristics of the material. For example, plastic bending is experienced when a pipeline is spooled onto a reel, and again later when it is unspooled at an installation site. Significant bending in the presence of tension is experienced during installation by the S-lay method, as the pipe conforms to the curvature of the stinger and beyond in the overbend region (see Figure 2.15). Bending in the presence of external pressure is experienced in the sagbend of all major installation methods (e.g., reeling, J-lay, S-lay, see Chapter 2) as well as in free-spans on the sea floor. Land pipelines can experience bending due to subsidence of the foundation, as illustrated in Figure 8.1. Subsidence can result from earthquake activity, from permafrost degradation and from other causes. Advances in directional drilling can also result in bending of tubulars. Figure 8.2 shows a pipeline being pulled through an underground river crossing. The borehole was pre-drilled by directional drilling. The pipeline conforms to the curvature of the hole, bending plastically in some cases. This chapter deals with the mechanics of inelastic bending and the associated limit states. The presentation will be extended in subsequent chapters to bending in the presence of tension and to combined bending and external pressure.
