SCC PROPERTIES OF MODIFIED ALLOY 718 IN BWR PLANT

摘要

A modified alloy 718 has been developed as an alternative material to nickel-based alloy X-750 used in the boiling water reactors (BWR). Stress corrosion cracking (SCC) of a jet pump beam made of alloy X-750, occurred in a BWR plant. In order to apply modified alloy 718 to the jet pump beam, an evaluation of resistance to SCC initiation based on a uni-axial constant load (UCL) test in high temperature water was carried out. All UCL test specimens of modified alloy 718 at an applied stress beyond the yield strength in 288°C showed no failure after 10,124 hours testing. On the other hand, UCL specimens of alloy X-750 at an applied stress of 900MPa failed within 10,000 hours. Therefore, it was confirmed that modified alloy 718 had longer SCC initiation time in high temperature water than alloy X-750. Moreover, fatigue and spring properties of modified alloy 718 were also evaluated, and the characteristics of both modified alloy 718 and alloy X-750 were compared.