Steam turbine blade and disc failures have occurred from time to time throughout the world. Although they are rare events, the implications for safety, for repair costs and for loss of availability are severe. Current operational and maintenance practices for any particular turbine design may be based on many years of satisfactory service. However, recent deregulation of the power industry in the UK and forthcoming deregulation in the USA may have an effect on operational and reliability issues, as changing operational demands are placed upon power generators through economic forces. In the UK in the 1990s with deregulation and privatization of power generation, the introduction of
high efficiency gas fired stations has transformed the profile of the industry. The nuclear stations, which can only operate safely under base load conditions, were protected by government regulation (the socalled
“nuclear levy”). These gas fired and nuclear plants, together with those coal-fired stations that have been fitted with flue gas desulfurization (FGD) systems, accounted for the majority of base load supply. The remaining coal-fired stations were, therefore, forced towards operating for peak demand rather than base load. They have had to develop operating procedures that enable them to provide power flexibly and economically with rapid response to variable demand. One of these procedures covers running up the unit to stable conditions before power is produced. This paper gives an account of the research carried out to confirm the risks of turbine damage, which was essentially due to corrosion during the start-up sequence. The paper illustrates the research that was carried out over 7 months using on-line corrosion monitoring with the electrochemical noise technique. Probes were installed directly within the low pressure (LP) section of an operating 500 MW turbine to gather data that would demonstrate the cause of pitting corrosion at the turbine blade root. This pitting had been found to be the primary factor in the onset of stress corrosion cracking (SCC), which
eventually caused the failure of a turbine blade with very serious consequences for the unit.