Based on the knowledge about microstructure stability a new alloy and a weld consumable will be designed to produce a compromise between high creep strength (between T91 and T92), high oxidation/corrosion resistance and good weldability. The alloy development should be based on a new concept of alloy design and tools based on thermodynamic and kinetic modelling. The possible application in welded water wall tube-fin constructions without the Post Weld Heat Treatment (PWHT), as well as, in thick pipes manufacture and welded joints with PWHT have to be demonstrated together with the relevant mechanical and oxidation/corrosion testing