Thermomechanical Analysis of a Pressurised Pipe Under Plant Conditions

This paper is concerned with the development of a methodology for thermo-mechanical analysis of high temperature, steam-pressurised P91 pipes in electrical power generation plant under realistic (measured) temperature and pressure cycles. In particular, these data encompass key thermal events, such as ‘load-following’ temperature variations and sudden, significant fluctuations in steam temperatures associated with attemperation events and ‘trips’ (sudden plant shut-down), likely to induce thermo-mechanical fatigue damage. An anisothermal elastic-plastic-creep material model for cyclic behaviour of P91 is employed in the transient FE model to predict the stress-strain-temperature cycles and the associated strain-rates. The results permit characterisation of the behaviour of pressurised P91 pipes for identification of the thermo-mechanical loading histories relevant to such components, for realistic, customised testing; this type of capability is relevant to design and analysis with respect to the evolving nature of power plant operating cycles, e.g. associated with more flexible use of fossil fuel plant to complement renewable energy sources.