Flexibility Factors and Stress Indices for Piping Components With D/T ≧ 100 Subjected to In-Plane or Out-of-Plane Moment

Abstract

The finite element analyses are carried out for the several piping components (D/T ≧ 100) subjected to in-plane or out-of-plane moment. For the stress evaluation of the chemical plant piping systems, ANSI B31.3 is usually applied. But the stress intensification factors and flexibility factors in this code are mainly for a heavy-wall-thickness pipe, so it is necessary to reconsider these factors for a thin-wall-thickness pipe with a large diameter. In our study, several finite element analyses using MSC/NASTRAN program were performed on the pipe bends (elbow or miter bend, 0.01 ≦ h ≦ 0.2) and the unreinforced fabricated tees (50 ≦ D/Tr ≦ 300, 0.5 ≦ d/D ≦ 0.95, 0.25 ≦ Tb/Tr ≦ 0.95), and the empirical formulas for the flexibility factors and the stress indices, due to out-of-plane or in-plane moment, were proposed. Experimental stress analyses for the piping components with D/Tr = 127 were also carried out, and it was confirmed that the results agreed well with the numerical ones.

Stress intensification factor, sustained stress index and flexibility factor analysis of large D/T elbows

“…As for the out-plane stress intensification factors, equations from literature 4,5,7 yield similar results, while the equation from literature [1][2][3] seems to be overly conservative, especially with increasing the D=T ratio.…”

“…Comparison of the equations existing in the open literature against the experimental data presented in Table 2 is given in Figures 9 and 10. As evidenced, equations from literature [1][2][3]5,7 for in-plane stress intensification factors yield similar results, while the equation from literature 4 seems to be overly conservative, especially with increasing the D=T ratio.…”

“…When in-plane flexibility factors are compared, a general conclusion can be drawn that the procedure proposed in literature 4 (i.e., constant in-plane flexibility factor of 1) tends to grossly underestimate the realistic in-plane flexibility factors, resulting in overly conservative design. Procedure from literature, 5 on the other hand, yields satisfactory results in the entire range of the numerical data.…”

“…Comparison of the out-plane flexibility factors shows that the equations from literature 4,5 (long radius) can be used with relative accuracy, while equation from literature 5 pertaining to short 2 against various equations for out-plane stress intensification factor. radius elbows tends to fail completely in the higher D 2 =ðR Á TÞ range (above $150) since it shows a clear drop in calculated values.…”

“…Excluding miter bends, which are not considered in this paper, a total of 10 finite element runs have been performed, 5 having short and 5 having long elbow radius. The authors 5 suggested to use different equations for short and long radius elbows, which is in general impractical and should be avoided, as there is clear dependence of the elbow design factors on its radius.…”