Bending Capacity of Pipes Subject to Point Loads

Large bending moments may develop on free pipeline lengths in the proximity of pipe sections subject to a local force. Sometimes the local force is such as to cause a partial loss of the sectional strength capacity of the pipe. This is the case of a pipeline plastically bent over the stinger of an S-lay barge, or of a pipeline laid on the sea bottom and hooked by an anchor or trawling gear, or of a pipe subject to cold bending when it is made to cope with sharp bottom roughness etc. In such conditions, the limit bending capacity of the pipe section, subject to local load effects, is significantly influenced. This aspect is not covered by international design codes and the scope of this paper is to show that, in some circumstances, it must be taken into due account. In this paper: • The relevant literature as concerns experimental tests, interpretative models, analysis methodologies and design approaches, is reviewed; • The FE model and post-processing, purpose-developed to investigate the interaction between local and global effect, are discussed; • The findings of FE analyses, in particular the effect of load combination, load history, pipe geometric characteristics and loading — magnitude and shape of the contact area, are presented. It is concluded that the limit bending capacity reduces significantly when local effects are such as to develop stresses on the pipe wall that affect the activation of the sectional buckling mechanism.