A comparison of failure assessment diagram options for Inconel 690 and Incoloy 800 nuclear steam generators tubes

Abstract

In the context of structural integrity assessment of cracked Steam Generator Tubes (SGTs), the Failure Assessment Diagram (FAD) has been proposed as a modern tool able to reduce the conservativeness of traditional plastic limit load analyses. As different FAD failure curves are available in the literature, this paper presents a comparison between the so-called Options 1, 2 and 3 FAD curves derived for Inconel 690 and Incoloy 800 nuclear SGTs. Detailed Option 3 curves are obtained from elastoplastic finite element analyses and experimental data from fracture tests. Material-specific Option 2 curves are drawn from stress vs. strain data of uniaxial tests of SGTs. It is shown that the simplest generic Option 1 curve is conservative but appropriate for structural integrity assessments of cracked nuclear SGTs in operation. Alternatively, Option 3 FAD curves must be used when an excessive conservatism shall be avoided.