Effect of Internal Pressure on Flexibility and Stress Intensification Factors for Pipe Elbows Analyzed by the Finite Element Method

摘要

A finite element analysis using NASTRAN was conducted on a 90-degree piping elbow subjected to an inplane bending load and internal pressures of 0, 400, and 800 psi. The objective of this study was to verify that the nonlinear effect of the superposition of internal pressure with inplane bending could be accounted for by employing a static analysis with differential stiffness. Flexibility factors and stress intensification factors were computed from the NASTRAN results. These numerical data were then compared to similar data obtained from experimental results. The flexibility factors and stress intensification factors were computed from the NASTRAN results were found to agree reasonably well with the experimental data. The NASTRAN values tended to be conservative in that they slightly overestimated the flexibilities and stresses. These differences might be attributed to such experimental factors as nonuniform pipe wall thickness, spacing of strain gages, and bending of tangent straight pipe extensions. In general, it is concluded that the differential stiffness capability in NASTRAN is adequate for accounting for the effects of internal pressure on flexibility factors and stress intensification factors.