Modelling Creep and Creep-Fatigue Damage for CSEF Power Plant Steels

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The current market conditions are such that combined cycle gas turbine (CCGT) plants are now considering double two-shift operation, so potentially accruing upwards of 600 starts per year. The pressure to reduce the extent of pressure system inspections and repairs continues to increase, with the most recent capacity auction clearing prices for generation showing a significant reduction when compared to previous years. For operators of large generation facilities the key consideration is the through life revenue return, which will guide decisions on new plant builds and any capital investments on plant currently operating. On this basis the need for effective life prediction and condition monitoring tools to support the supply chain (designer, fabricator, operator and technical service provider) is evident.Over the years, significant development has been made on the 9-12%Cr creep strength enhanced ferritic (CSEF) steels. Traditionally, in material development for power plant components, creep ductility, which can be treated as resistance to damage, has received much less attention. However, the risk of catastrophic failure due to low damage tolerance is a real challenge, in particular, in the situation where mechanical and metallurgical constraints are present. In addition, due to the increasing frequency of cyclic operations, i.e. starts up and shut downs for main steam pipelines of power plants, low cycle creep fatigue failure due to low ductility of the materials has become an important concern.The aim of the proposed project is to investigate creep and creep fatigue behaviour which takes into account the variable ductility for CSEF power plant steels, through a comprehensive theoretical, experimental and computational programme.Specific objectives will include:1. Data acquisition/analysis and critical review on the currently available models and assessment procedure.2. Experimental/physical understanding of creep and creep fatigue behaviour of CSEF power plant steels with different initial ductility.3. Development of a novel creep and creep fatigue model which takes into account the variable ductility.4. Application of the model for component assessment using the operational data from a modern CCGT plant.High temperature mechanical testing and physical characterization will be carried out using well-established facility. The theoretical and modelling work will be carried out using finite element package ABAQUS through user defined subroutines.