Prediction Method for Plastic Collapse of Pipes Subjected to Combined Bending and Torsion Moments

Abstract

When a crack is detected in a pipe during in-service inspection, the failure estimation method given in the codes such as ASME Boiler and Pressure Vessel Code Section XI non-mandatory Appendix C or JSME S NA-1-2008 Appendix E-8 can be applied to assess the integrity of the pipe. In the current editions of these codes, the failure estimation method is provided for bending moment and pressure. Torsion load is assumed to be relatively small and is not considered in the method. In this paper, finite element analyses are conducted for 24-inch stainless steel pipe with a circumferential surface crack subjected to the combined bending and torsion moments, focusing on large and pure torsion moments. Based on the analysis results, a prediction method for plastic collapse under the combined loading conditions of bending and torsion is proposed for the entire range of torsion moments.

Collapse load analysis for circumferentially cracked cylinder subjected to combined torsion and bending moments

“…Li [6] also found that for any crack depth and crack angle, the value of is almost equal to 1. However, there is some difficulties in using Eq.…”

“…This implies that �� can be used to predict the collapse plastic failure for the case of small amount of torsion. As �� is not valid for the case of large torsion moment, Li et al [6] defined a non-dimensional failure parameter r which can be used to estimate the collapse failure of cylinder for general magnitude of torsion moment. This parameter is given by…”

“…(5) can provide accurate prediction only for the case of short cylinder length or shallow surface crack [6,8].…”

“…This solution is derived based on the NSC approach. For the case of constant-depth crack, the solution is given as follows [6];…”

“…At present, several methods for predicting the failure load of cracked cylinder under combined torsion and bending moments have been developed. These methods are based on the equivalent collapse moment and biaxial failure parameter [5,6]. However, these methods still have some limitations when they were used to estimate the failure load.…”