Necking in Abaqus

Dear all
I am modeling a steel pipe under cyclic loading. The ultimate strain demand of the pipe is expected to be around 10%. So theoretically necking is not expected. However, during the analysis, at final cycles with strain demand of 9-10 %, the pipes starts to neck . I refined the mesh but the necking still occurs. Oks note that the model does not include damage model and only a combined hardening rule has been specified fir steel. Does anyone know what is the origin of such a necking?