Probabilistic cyclic constitutions are investigated and safety assessment on the ASME code-based design curves is given to 0Cr18Ni10Ti pipe steel. Incremental and group fatigue tests were carried out respectively to reveal the cyclic deformation and life characteristics. The results showed that the material acted as cyclic strengthening and masing behaviour. A phenomenon of random cyclic constitutions was observed. The modified Ramberg-Osgood equation combining an assumption of the cyclic stress amplitude following normal distribution is applied to describe the constitutions. Fine modeling effect is obtained on both considerations of survival probability and confidence. Probabilistic characteristics are also given to the fatigue virtual stress amplitude-life relations and then a safety assessment is carried out on the design curves. The results exhibit that the ASME curves with constant reduction factors are not matching the evolutionary scattered statistical trend of fatigue lives. The curves with 2 reduction factor on stress amplitude and 20 on fatigue life are much conservative for the present material, which is great different from the previous observation to weld metal. It indicates that the fatigue design by analysis for the piping should be based appropriately on the welded joint data.