Steels exposed for long periods of time at high temperatures in power platn undergo microstructural changes, which degrade their properties and hence limit the safe operational life expectancy of key components manufactured from these materials. In order to assess their suitability for further periods of service beyond the original plant design life, an evalaution of their metallurgical condition is required. This can often be achieved by monitoring microstructural changes in the steel, which occur due to thermal and material deformation effects during service exposure. These changes can often be correlated with measurements of the changing mechanical properties of the steel, or used to assess the time-temperature history of the component using relationships estabilished from studies performed on long-term creep exposed samples of the steel in question.
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