Experimental and Nonlinear FEA Investigation of Elbow Leading to a New Definition of the B2 Stress Index

Abstract

This study suggests a new margin-consistent procedure for the calculation of the B2 stress index for any piping component, which is the ratio of the collapse moment of a corresponding straight pipe to the collapse moment of the piping component. It gives a B2 value of 1.00 when applied to a straight pipe and a safety margin for the component that is always the same as for the straight pipe. An example of using this definition to calculate the value of B2 is provided. To obtain the collapse moments of piping components, either finite element analysis (FEA) or experiments can be used. This work gives a brief review of nonlinear FEA modeling procedures. Then nonlinear FEA using ANSYS shell models and ABAQUS elbow models are used to simulate two tests on straight pipes and eight tests on elbows under in-plane closing, in-plane opening and out-of-plane bending. Constitutive models and welding effects are discussed. All correlations between FEA and measured experimental results for the load-displacement curves are excellent. It is concluded that nonlinear FEA using ANSYS SHELL181 and ABAQUS ELBOW31 can give quite accurate predictions of the global behavior of elbows and straight pipes under monotonic loading. A very preliminary study for B2' stress index for cyclic loading is also performed, in which two elbow tests subjected to quasi static in-plane cyclic loading were simulated.