Meridian Stresses in Thin-Walled Steel Pipes as Reason for Cross-Sectional Ovalization

This work was motivated by the need for providing designers with more effective rehabilitation procedures. The initial step taken was to assess the ovality of the cross sections of thin-walled, cylindrical, high-pressure steel pipelines. Transition pipelines are exposed to the influences of combined loads (internal pressure, longitudinal force, and bending moment). These loads usually appear in places where hazardous conditions exist, such as landslides, soil subsidence, and changing temperatures, among others. Determining the ovality caused by meridian stresses after unloading the pipe sections is vital to the rehabilitation process. Internal pressure, bending moment, longitudinal force, and distribution of stresses and strains in the pipe cross section were analyzed using a new engineering approach to estimate the ovality after the unloading of the pipe element. A pipe with isotropic steel material properties in compressed and tensile hardening regions was considered. A stress-strain diagram of pipe materials was approximated using linear and power law. The approach consisted of two parts: investigation of beam-type load factors that cause elastic-plastic deformations in the pipe element without losing cross-sectional circular stability (ovalization), and determination of the radial and hoop displacements after loading and unloading. The theory of plasticity and the membrane theory of shells were used to reduce problems to the beamlike pipe. The results of the analytical study showed critical moment and curvature of the longitudinal pipe axis that correspond to maximum allowable ovality of the pipe. Variations of internal pressure during the pipe’s bending were compared with experimental outcomes.