Finite Element Analysis of the Ultimate Strength of Industrial Pipes Under Bending and Pressure
by Dimitris Tsouvalas
Diploma Thesis, September 2003

ABSTRACT

The work examines the nonlinear elastic-plastic response of internally pressurized 90 deg pipe elbows under in-plane and out-of-plane bending. Nonlinear shell elements from a general-purpose finite element program are employed to model the inelastic response of steel elbows and the adjacent straight parts. The numerical results are successfully compared with real-scale experimental measurements. The work also presents a parametric study, aimed at investigating the effects of diameter-to-thickness ratio and moderate pressure levels on the ultimate bending capacity of 90 deg elbows, focusing on the failure mode (local buckling or cross-sectional flattening) and the maximum bending moment. Special attention is given to the response of 90 deg elbows under out-of-plane bending moments.

	Devises for measuring rotations and ovalization in specimen 80, for out-of-plane bending moments in an elbow specimen tested at TNO, The Netherlands. Note the 45 deg orientation of the ovalizaton devises with respect to the pipe axis, so that the maximum ovalization of the cross-section is measured.
Buckled shapes of thin-walled Elbow I (D/t=90) under out-of-plane bending moments; for zero pressure (left), for pressure level 40% of the plastic (yield) pressure (right).