The propensity of a pipeline to develop lateral deflection due to severe service conditions (high pressure/high temperature), the definition of appropriate mitigation measures to control the development of excessive bending deformations, both can be analysed by means of simplified analytical tools instead of using more sophisticated FEM analysis. The main advantage of using analytical predictive models is that simple relationships correlate pipe response to main structural parameters. In HOTPIPE Project, effort has been dedicated to the development of simplified procedures suitable for analysing the post buckling configuration of a pipeline subject to both isolated buckling modes and in presence of a random sequence of buckling activators possibly involving complex pipeline configuration (expansion loops, crossings, intervention works, etc.). Particular attention has been dedicated to localisation of thermal expansion in one single buckle in presence of random and regular/purpose made sequence of imperfections/deviations from a rectilinear axis.
When a pipeline resting on the seabed is operated at high pressure and high temperature, it develops lateral bending to recover thermal expansion. If the line is restrained by soil friction, axial compressive load develops for increasing temperatures and, at some critical value, the pipe may experience lateral deformation/bending paths activated by initial misalignments. As soon as the pipeline starts deflecting laterally, the initial resistance of the line to develop lateral deflection is reduced at such locations. Depending on how the thermal expansion/restraint develops, the pipeline may "slip" from adjacent sections into one isolated buckle. An equilibrium is achieved when the mobilised friction equilibrates the axial force in the buckle. The axial compressive force within the buckle depends on the length and modal shape. The release of the axial compressive force as a consequence of the lateral bending is gradual from an anchoring point through the two adjacent lengths feeding into the buckle.
