Local buckling of UOE and seamless steel pipes

The compressive strain at which local buckling occurs, depends on many factors. These are the geometry (diameter to wall-thickness ratio, imperfections), the loading conditions (bending moment, normal force, internal or external pressure, etc.), residual stresses, the shape of the stress strain diagram and the strength of the steel in longitudinal and circumferential direction. Test results show considerable scatter. In a research program for PRCI, four bending tests on 20-inch pipes were carried out. Also a survey of relevant test results from other sources was carried out. It appears that the manufacturing method (seamless, UOE) has a considerable influence on the critical buckling strain. These were compared with available prediction formulae for the bending moment capacity and the critical strain. Statistical and probabilistic evaluations were carried out to determine the best design formulae and appropriate safety factors. An overview is given of the bending tests on three 20-inch UOE manufactured pipes and one seamless pipe with D/t ratios 45, 27, 22 and 29. The main results of the statistical and probabilistic evaluations are presented. The factors that govern the performance in bending moment capacity and the critical buckling strain are briefly discussed.