B2 stress indices for thin walled straight pipes with D/t > 50 and imperfections

The design equations for primary loads of piping components in the ASME Boiler and Pressure Vessel Code (ASME Code) are based on the B1 and B2 stress indices. In the present studies the B2 stress indices of thin-walled straight pipes with D/t-ratios 20 ≤ D/t ≤ 140 are determined using FE analyses. The analyses are performed for pipes made of ideal elastic-plastic materials and some selected steels. The B2 index is calculated from the maximum bending moments obtained by nonlinear FE analyses. For the calculation of the B2 indices for straight pipes with 40 < D/t ≤ 100 a formula derived in previous works is used. The obtained B2 indices are only valid if they satisfy an additional relation, which follows from the design equation for primary loads. Formulas for the dependency of the B2 indices from the D/t ratio and the yield stress are given. Finally, conservative equations for the determination of B2 indices for ferritic and austenitic straight pipes are derived. For ferritic pipes there is a good agreement with the B2 indices according to the ASME Code. In difference to the ASME Code the temperature dependency need not be considered for ferritic pipes. The B2 indices for austenitic pipes with D/t = 100 are 33% larger than the values of the ASME Code. The background for the deviations is explained.