The aim of the PhD project is to investigate the creep and creep fatigue behaviours of CSEF power plant steels subject to realistic plant loading cycles.
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 PhD project is to investigate creep and creep fatigue behaviour which takes into account the variable ductility for CSEF power plant steels subject to realistic plant loading cycles, through a comprehensive theoretical, experimental and computational programme.
Specific objectives will include:
1. Data acquisition and analysis and literature review on the currently available models and assessment procedure. 2. Experimental investigation of LCF behaviour and microstructure characterization of the candidate power plant steel/weld (possibly MARBN). 3. Development of a cyclic visco-plasticity model for PM, WM and HAZ which takes into account the cyclic softening and damage. 4. Application of the model for component assessment using plant operational data and considering typical plant component geometries and plant operator requirements for condition assessment. 5. Exploring early life contributors to damage such as severe plant operation, impact of poor design and creep brittle properties.
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.
The candidate must have a high-grade qualification, at least the equivalent of a UK 1st or 2.1 class degree in an engineering or science discipline (e.g. mechanical engineering or applied mechanics). A strong background of Mechanics of Solids and Computational Modelling is preferable. The students must possess excellent presentation and communication skills and be able to write high quality academic papers.
The PhD project is of four years duration, starting October 2019, within the EPSRC Centre for Doctor Training (CDT) “Resilient decarbonised Fuel Energy Systems”. The studentship which will cover full university fees and a tax-free, enhanced annual stipend of £18,757 to UK candidates. A limited amount of partial funding is available for exceptional international applicants who are highly qualified and motivated. Due to the nature of this funding, the CDT would only be able to cover the cost of the Home/EU fees and therefore the applicant would need to either find alternative funding or self-fund the fee difference.
1. Parker JD. Factors affecting cyclic performance of tempered martensitic steels. ASME PVP Conf. Vancouver, Canada, 17–21 July, 2016. Paper No. PVP2016-63980. 2. Hyde TH, Sun W. Some issues on creep damage modelling of welds with heterogeneous structures. Int. J. Mech. Mater. Des. 5 (4), 327-335, 2009. 3. Plesiutschnig E, Beal C, Paul S, Zeiler G, Sommitsch C. Optimised microstructure for increased creep rupture strength of MarBN steels. Mats. High Temp. 32. 318-322, 2015. 4. Benaarbia A., Xu X., Sun W., Becker A. A., Osgerby S. Characterization of cyclic behaviour, deformation mechanisms, and microstructural evolution of MarBN steels under high temperature conditions. Int. J. Fatigue. 131, 2020, 105270.
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