PVP2011-57731 Effects of Bending Moment and Torsion on the Internal Pressure Limit Load of Locally Thinned Pipes

The pipe wall thinning stress evaluation procedures in Code-Case N-597-2 [1] of the ASME Boiler and Pressure Vessel (B&PV) Code are essentially based on Construction Code [2] stress evaluation. Stresses in the hoop and the axial directions are evaluated separately to meet the Construction Code allowable stress. Using Construction Code rules for local pipe wall thinning stress evaluation in Class 2 & 3 piping may be too restrictive. An alternative approach is to use the limit loads of locally wall thinned pipe in conjunction with an appropriate Z-Factor and the structural factors of the ASME B&PV Section XI, Appendix C [3]. Such approach may require a combined effect of pressure, bending, axial load and torsion loads on locally thinned pipe. In this paper, the effects of bending moment and torsion on the internal pressure limit load of locally thinned straight pipes are investigated. Large strain finite element limit load analysis with elastic- perfectly plastic materials are performed for a parametric matrix of piping models with various pipe R/t ratios, flaw depths, axial and transverse flaw extents. Based on the results, the allowable pressure for axial flaws in C-5420 of the ASME B&PV Section XI, Appendix C [3] may be used for piping local wall thinning as an alternative evaluation procedure to the current minimum pipe wall thickness evaluation procedure in th