Advanced ultra-supercritical fossil plants operated at 700/725 °C and up to 350 bars are currently planned to be realized in the next decade. Due to the increase of the steam parameters and the use of new materials e.g. 9-11%Cr steels and nickel based alloys the design of highly loaded components is approaching more and more the classical design limits with regard to critical wall thickness and the related tolerable thermal gradients. To make full use of the strength potential of new boiler materials but also taking into account their specific stress-strain relaxation behavior, new methods are required for reliable integrity analyses and lifetime assessment procedures. Numerical Finite Element (FE) simulation using inelastic constitutive equations offers the possibility of “design by analysis” based on state of the art FE codes and user-defined advanced inelastic material laws. Furthermore material specific damage mechanisms must be considered in such assessments. With regard to component behavior beside aspects of multiaxial loading conditions must be considered as well as the behavior of materials and welded joints in the as-built state. Finally an outlook on the capabilities of new multi-scale approaches to describe material and component behavior will be given.

For plants with ultra critical steam conditions with live steam temperatures up to 720°C and pressure up to 300 bars optimized materials are required. These are a ferritic-bainitic material (T24) for applications up to 550°C, modified 9 Cr steels (E911 and P92), a new Co-alloyed martensitic 12 Cr steel for usage up to 630°C and Nickel based alloys (Alloy 617) for temperatures above 650°C. Experimental work has been done to create a reliable data base for design and inspection. Special emphasis was put on long term creep characteristics of base material with specific consideration of cross welds, microstructural investigations with regard to optimization of chemical composition and heat treatment and numerical modeling.