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 ismainly made of A106 Gr.B, carbon steel piping but due toflow-accelerated corrosion (FAC), some parts of thesystem use A335 P22 piping, which is a 2.25Cr-1Moalloy. Athough P22 mitigates FAC, it raises weldabilityissues, and the high price of Mo makes it an expensiveoption. In this context, two low alloy steels with higherCr to compensate for lower Mo content (, 3.2Cr-0.5Mo,and 4.2Cr) have been manufactured and theirmicrostructure, chemistry, and mechanical propertiescompared against 2.25Cr-1Mo material. To confirm thatFAC resistance is not compromised by reducing Mocontent, FAC experiments at 150 °C with flow velocity5.7 m/s wer conducted for all the alloys. Results show thatthe beneficial effect of Cr on corrosion resistancedominates over any effect of decreasing Mo content.These Cr- and Mo-containing steels form two oxide layersunder FAC condition: a Cr-rich outer and a CrsubstitutedFe3O4 inner oxide. Reducing Mo content inthe base material does not compromise the FACresistance imparted by the high Cr content.