A review of the LICON methodology for predicting the long term creep rupture strength of materials

• LICON is an approach for predicting long term uniaxial creep strength from short duration multi-axial creep tests.
• Recommendations are summarised for application of the LICON method for different material-conditions.
• Successful application of the method for 9% and 1%Cr steels and a dissimilar metal weld has been reviewed.

In the late 1990s, an advanced iso-thermal extrapolation approach referred to as the LICON methodology was developed in a European Brite Euram project to predict the long term creep rupture behaviour of new generation steels. This methodology relies on multiaxial loading conditions to accelerate the onset of long time creep damage formation into the short time rupture regime. The LICON method therefore enables the prediction of long time uniaxial creep rupture strengths using the results from several short duration multiaxial creep crack initiation tests in conjunction with the outcome of a mechanical analysis for the adopted multiaxial specimen geometry. This paper briefly reviews the latest findings concerning application of the LICON method for different types of materials. Successful applications of the method for long time creep rupture strength predictions of advanced martensitic 9%Cr pipe steels (i.e. P91, E911 and P92), a low alloy ferritic steel (i.e. 1CrMoV) and a dissimilar metal weld (1CrMoV/Inconel 617/Inconel 625) have been successfully achieved during the last 15 years. These evaluations have well proven the applicability of the LICON concept for different types of engineering materials while at the same time emphasising the need for i) consideration of appropriate mechanical analysis tools for the assessment of the multiaxial geometry used for creep crack initiation tests dependent on the type of material/structure under investigation and ii) consideration of the complex multiaxial stress state developing within the constituent parts of weldments, even within a uniaxial testpiece.