Failure assessment diagrams for use in R6 assessments for austenitic components

The third revision of the defect assessment procedure R6 extended the scope of earlier versions, which addressed high strength ferritic steels, to a more general class of material behaviour. In particular, it allowed assessments to be made of defective austenitic components. This paper reviews the background to the R6 procedures and the various options in revision 3 for deriving the failure assessment curve. The most complex option, termed option 3, involves the derivation of failure assessment curves from J values. This option is examined using experimental data from austenitic specimens of various geometries and crack sizes, and using finite-element data including analysis of a surface defect in a plate. It is demonstrated that option 3 curves lie close to approximate material-specific curves, termed option 2, which are derived from uniaxial stress/strain data. Option 2 curves are derived for austenitic steels and weld metals over a wide range of temperatures. It is shown, particularly for parent austenitic steels, that the material-specific curves are sensibly independent of temperature and are close to the general purpose, option 1, failure assessment curve presented in R6. Thus, it is concluded that it is appropriate to use the simple option 1 curve for defect assessments of austenitic components.