Development of Mo-free Low Alloy Steels for Mitigation of Flow-Accelerated Corrosion in Secondary Side of PWRs

摘要

The secondary side of pressurized water reactors is mainly made of A106 Gr.B, carbon steel piping but due to flow-accelerated corrosion (FAC), some parts of the system use A335 P22 piping, which is a 2.25Cr-1Mo alloy. Athough P22 mitigates FAC, it raises weldability issues, and the high price of Mo makes it an expensive option. In this context, two low alloy steels with higher Cr to compensate for lower Mo content (, 3.2Cr-0.5Mo, and 4.2Cr) have been manufactured and their microstructure, chemistry, and mechanical properties compared against 2.25Cr-1Mo material. To confirm that FAC resistance is not compromised by reducing Mo content, FAC experiments at 150 °C with flow velocity 5.7 m/s wer conducted for all the alloys. Results show that the beneficial effect of Cr on corrosion resistance dominates over any effect of decreasing Mo content. These Cr- and Mo-containing steels form two oxide layers under FAC condition: a Cr-rich outer and a Cr-substituted Fe_3O_4 inner oxide. Reducing Mo content in the base material does not compromise the FAC resistance imparted by the high Cr content.