Modern power stations generate electricity using steam-powered turbines. To achieve maximum efficiency, steam temperatures need to be kept as high as possible for as long as possible. This means that pipe work and other steam-carrying channels could be required to operate at temperatures of up to 6500C for up to 40 years.
However, at the moment it is impossible to check what happens to these steels after 40-50 years because most of the advanced steels now used in power stations have only been in service for up to 20 years. This also makes the development of better steels difficult.
Now, research taking place at Loughborough University (with funding from the Swindon based Engineering and Physical Sciences Research Council and the power industry) aims to help out.
The researchers at Loughborough, working in close collaboration with two Japanese universities: the University of Hokkaido and the University of Tohoku, have devised mathematical models that show how power station steels behave at the nanoparticle level. The small changes that take place at this scale determine the strength of the steel. Therefore the models provide the only way in which designers of electricity generating plants can forecast the behaviour of different steels on this timescale.
The initiative involves studying the microstructure of steels after long-term exposure at various temperatures and using this information to verify the models’ accuracy. The models can then be used to predict how a steel’s properties could be changed using heat treatment or other techniques.
The validity of the mathematical models is constantly checked by observing real steel with a transmission electron microscope. This is a high-powered microscope that can produce images of materials’ microstructure with a resolution of around 0.2 nanometres.
Based on the information obtained from the nanoscale modelling, the work is now extending into predicting the changing strength of power station steels as a function of service life.
The properties of grain boundaries in steel are a particular focus of the Loughborough project. These boundaries have an important influence on steel’s properties at high temperatures. The team will be using TECNAI F20 FEGSTEM and JEOL 2000FX transmission electron microscopes to study these boundaries in more detail. A parallel study is ongoing in which several of the Loughborough group will spend time working on a new ARM1300 multi beam million volt electron microscope, equipped with an ion beam line, at Hokkaido University. This is the first machine of its kind in the world and considerable progress is anticipated in the study of grain boundaries using this enhanced capability.
The project team at the University’s Institute of Polymer Technology and Materials Engineering is led by Professor Roy Faulkner, who says: ‘Our work could have tangible benefits, in terms of improving power station operation and keeping down the price of the electricity.’
The research initiative has received total funding from the UK Engineering and Physical Sciences Research Council and from the power industry of over £1.5 million over the last two years.