Effect of UOE Forming Process on the Buckling Strains of Steel Pipes

The main findings of our studies are:

1. The apparent true stress-strain relations for the curved pipe are found to differ from those for the flat steel plate used to form the pipe.
2. For the curved pipe, the FEA-predicted apparent hoop stress-strain relation is found to have a higher apparent yield point and a milder strain hardening than that based on the FEA-predicted apparent longitudinal stress-strain relationship. The observation is consistent with past experimental results on tensile test coupons.
3. Buckling strains predicted by the detailed model that capture the effects of UOE forming are found to be significantly smaller than those based on the simplified model that omits the effects of UOE forming. The finding is consistent with the fact that critical strains measured in past experimental results have been consistently lower than those predicted by FEA models that do not include the UOE forming process. The critical strains predicted by the detailed FEA model are thus closer to those predicted by the provisions at the design standard CAN CSA Z662.
4. The detailed modelling approach developed in the present study is believed to provide more accurate predictions of buckling strains in pipes than other modelling techniques that omit residual stresses induced by the UOE forming process. It is recommended to apply the proposed technique to pipe geometries that have been tested to further assess the accuracy of the predictions of buckling strains in pipes based on technique developed.
5. The detailed modelling approach developed in the present study offers a promising numerical low-cost approach to extend the existing database of experimentally measured critical strains. It is recommended to adopt the new technique to predict critical strains for other steel pipe configurations, steel grades, loading conditions.

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