Effect of tempering on bending-induced material strength inhomogeneity in hydrogenation reactor shells

Bending forming causes significant inhomogeneous material strength distribution (MSD) in hydrogenation reactor shells. Tempering can improve this problem before the long-term service of hydrogenation reactors, but its effect is still unclear. In this work, we investigated the impact of tempering on the material strength inhomogeneity in hydrogenation reactor shells. First, 650 °C plastic deformation as well as 705 °C × 8 h tempering was performed on 2.25Cr–1Mo-0.25V tensile specimens. Yield strength (YS) and ultimate tensile strength (UTS) of these specimens were measured. Then, an artificial neural network (ANN) was constructed based on the experimental results, and it was further utilized to establish MSD prediction model that can predict actual MSDs in ring shells before and after tempering. Thereafter, the tempering effect was discussed in details via comparing predicted MSDs in un-tempered and final reactor shells. At last, the tensile specimens were also observed by scanning electron microscope (SEM). Image identification technology was applied in obtained SEM profiles to quantitatively analyze size and number of carbides. Results showed that the maximal absolute relative errors were 4.97% and 7.89% for ANN and MSD predictor, respectively. The coarsening behavior of carbides could explain the discrepancy in strength after tempering between 2.25Cr–1Mo-0.25V steels with different warm deformation extents. This work will contribute to the lightweight design of hydrogenation reactors.